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*********
Welcome to Project 64!
The goal of Project 64 is to preserve Commodore 64 related documents
in electronic text format that might otherwise cease to exist with the
rapid advancement of computer technology and declining interest in 8-
bit computers on the part of the general population. If you would like
to help by converting C64 related hardcopy documents to electronic
texts please contact the manager of Project 64, Cris Berneburg, at
<74171.2136@compuserve.com>.
Extensive efforts were made to preserve the contents of the original
document. However, certain portions, such as diagrams, program
listings, and indexes may have been either altered or sacrificed due
to the limitations of plain vanilla text. Diagrams may have been
eliminated where ASCII-art was not feasible. Program listings may be
missing display codes where substitutions were not possible. Tables
of contents and indexes may have been changed from page number
references to section number references. Please accept our apologies
for these limitations, alterations, and possible omissions.
The author(s) of the original document and members of Project 64 make
no representations about the accuracy or suitability of this material
for any purpose. This etext is provided "as-is". Please refer to the
warantee of the original document, if any, that may included in this
etext. No other warantees, express or implied, are made to you as to
the etext or any medium it may be on. Neither the author(s) nor the
members of Project 64 will assume liability for damages either from
the direct or indirect use of this etext or from the distribution of
or modification to this etext.
*********
The Project 64 etext of the Commodore 64 Programmer's Reference Guide,
first edition. Converted to etext by Ville Muikkula. Some errors in
the original document were corrected in this etext.
C64PRG10.TXT, June 1996, etext #46
*********
~
I would like to thank the following persons for their valuable help:
Jouko Valta for the memory maps on pages 310-334.
Marko Makela for the combined table of memory maps on pages 264-266.
Cris Berneburg for proof reading.
Kimmo Hamalainen for proof reading.
There was a lot of work, but finally, after five weeks of correcting
OCR-errors and formatting the text to readable format, it is ready. I
hope that this massive project shows to the C= community that it is in
a fact possible for one man to convert a 500 page book to ASCII text.
One just have to be dedicated, believe that it can be done and have
the PATIENCE for it... and lots of free time. So, who's going to etext
Inside Commodore DOS?
If you find errors in the text, please report them so that they can
be fixed. There should not be many, though...
There are some pictures missing on pages 132,157,162-163,195,364-365,
377-378,380-381,404,406-407,416-417,421,459,476-477 and 481. Also the
schematics of C-64 are not available. I apologize for the possible
inconvenience this might cause.
Ville Muikkula <vmuikku@yrttis.ratol.fi> or <vmuikku@raahenet.ratol.fi>.
*********
Note: To extract the ascii text basic programs all at once from this
etext use "tok64" by Cris Berneburg <74171.2136@compuserve.com>.
*********
Windows 95 MS-DOS Edit is the ideal program for reading this
etext. Just check that ANSI.SYS is loaded in CONFIG.SYS and issue
the command:
mode con lines=50
Now a whole page fits nicely on the screen and you can use Page Up/Page
Down keys to flip pages. Just be sure that the ~ characters are always
on the last line of the screen.
*********
~
COMMODORE 64
PROGRAMMER'S
REFERENCE GUIDE
Published by
Commodore Business Machines, Inc.
and
Howard W. Sams & Co., Inc.
i
~
FIRST EDITION
FOURTH PRINTING-1983
Copyright (C) 1982 by Commodore Business Machines, Inc.
All rights reserved.
This manual is copyrighted and contains proprietary information. No part
of this publication may be reproduced, stored in a retrieval system, or
transmitted in any form or by any means, electronic, mechanical, photo-
copying, recording, or otherwise, without the prior written permission
of COMMODORE BUSINESS MACHINES, Inc.
ii
~
TABLE OF CONTENTS
INTRODUCTION ....................................................... ix
o What's Included? .............................................. x
o How to Use This Reference Guide ............................... xi
o Commodore 64 Applications Guide ............................... xii
o Commodore Information Network ................................. xvii
1. BASIC PROGRAMMING RULES ......................................... 1
o Introduction .................................................. 2
o Screen Display Codes (BASIC Character Set) .................... 2
The Operating System (OS) ................................... 2
o Programming Numbers and Variables ............................. 4
Integer, Floating-Point and String Constants ................ 4
Integer, Floating-Point and String Variables ................ 7
Integer, Floating-Point and String Arrays ................... 8
o Expressions and Operators ..................................... 9
Arithmetic Expressions ...................................... 10
Arithmetic Operations ....................................... 10
Relational Operators ........................................ 12
Logical Operators ........................................... 13
Hierarchy of Operations ..................................... 15
String Operations ........................................... 16
String Expressions .......................................... 17
o Programming Techniques ........................................ 18
Data Conversions ............................................ 18
Using the INPUT Statement ................................... 18
Using the GET Statement ..................................... 22
How to Crunch BASIC Programs ................................ 24
2. BASIC LANGUAGE VOCABULARY ....................................... 29
o Introduction .................................................. 30
o BASIC Keywords, Abbreviations, and Function Types ............. 31
o Description of BASIC Keywords (Alphabetical) .................. 35
o The Commodore 64 Keyboard and Features ........................ 93
o Screen Editor ................................................. 94
iii
~
3. PROGRAMMING GRAPHICS ON THE
COMMODORE 64 .................................................... 99
o Graphics Overview ............................................. 100
Character Display Modes ..................................... 100
Bit Map Modes ............................................... 100
Sprites ..................................................... 100
o Graphics locations ............................................ 101
Video Bank Selection ........................................ 101
Screen Memory ............................................... 102
Color Memory ................................................ 103
Character Memory ............................................ 103
o Standard Character Mode ....................................... 107
Character Definitions ....................................... 107
o Programmable Characters ....................................... 108
o Multi-Color Mode Graphics ..................................... 115
Multi-Color Mode Bit ........................................ 115
o Extended Background Color Mode ................................ 120
o Bit Mapped Graphics ........................................... 121
Standard High-Resolution Bit Map Mode ....................... 122
How It Works ................................................ 122
o Multi-Color Bit Map Mode ...................................... 127
o Smooth Scrolling .............................................. 128
o Sprites ....................................................... 131
Defining a Sprite ........................................... 131
Sprite Pointers ............................................. 133
Turning Sprites On .......................................... 134
Turning Sprites Off ......................................... 135
Colors ...................................................... 135
Multi-Color Mode ............................................ 135
Setting a Sprite to Multi-Color Mode ........................ 136
Expanded Sprites ............................................ 136
Sprite Positioning .......................................... 137
Sprite Positioning Summary .................................. 143
Sprite Display Priorities ................................... 144
Collision Detects ........................................... 144
o Other Graphics Features ....................................... 150
Screen Blanking ............................................. 150
Raster Register ............................................. 150
Interrupt Status Register ................................... 151
Suggested Screen and Character Color Combinations ........... 152
iv
~
o Programming Sprites-Another Look .............................. 153
Making Sprites in BASIC-A Short Program ..................... 153
Crunching Your Sprite Programs .............................. 156
Positioning Sprites on the Screen ........................... 157
Sprite Priorities ........................................... 161
Drawing a Sprite ............................................ 162
Creating a Sprite ... Step by Step .......................... 163
Moving Your Sprite on the Screen ............................ 165
Vertical Scrolling .......................................... 166
The Dancing Mouse-A Sprite Program Example .................. 166
Easy Spritemaking Chart ..................................... 176
Spritemaking Notes .......................................... 177
4. PROGRAMMING SOUND AND MUSIC
ON YOUR COMMODORE 64 ............................................ 183
o Introduction .................................................. 184
Volume Control .............................................. 186
Frequencies of Sound Waves .................................. 186
o Using Multiple Voices ......................................... 187
Controlling Multiple Voices ................................. 191
o Changing Waveforms ............................................ 192
Understanding Waveforms ..................................... 194
o The Envelope Generator ........................................ 196
o Filtering ..................................................... 199
o Advanced Techniques ........................................... 202
o Synchronization and Ring Modulation ........................... 207
5. BASIC TO MACHINE LANGUAGE ....................................... 209
o What is Machine Language? ..................................... 210
What Does Machine Code Look Like? ........................... 211
Simple Memory Map of the Commodore 64 ....................... 212
The Registers Inside the 6510 Microprocessor ................ 213
o How Do You Write Machine Language Programs? ................... 214
64MON ....................................................... 215
o Hexadecimal Notation .......................................... 215
Your First Machine Language Instruction ..................... 218
Writing Your First Program .................................. 220
o Addressing Modes .............................................. 221
Zero Page ................................................... 221
The Stack ................................................... 222
v
~
o Indexing ...................................................... 223
Indirect Indexed ............................................ 223
Indexed Indirect ............................................ 224
Branches and Testing ........................................ 226
o Subroutines ................................................... 228
o Useful Tips for the Beginner .................................. 229
o Approaching a Large Task ...................................... 230
o MCS6510 Microprocessor Instruction Set-
Alphabetic Sequence ........................................... 232
Instruction Addressing Modes and
Related Execution Times ................................... 254
o Memory Management on the Commodore 64 ......................... 260
o The KERNAL .................................................... 268
o KERNAL Power-Up Activities .................................... 269
How to Use the KERNAL ....................................... 270
User Callable KERNAL Routines ............................... 272
Error Codes ................................................. 306
o Using Machine Language From BASIC ............................. 307
Where to Put Machine Language Routines ...................... 309
How to Enter Machine language ............................... 309
o Commodore 64 Memory Map ....................................... 310
Commodore 64 Input/Output Assignments ....................... 320
6. INPUT/OUTPUT GUIDE .............................................. 335
o Introduction .................................................. 336
o Output to the TV .............................................. 336
o Output to Other Devices ....................................... 337
Output to Printer ........................................... 338
Output to Modem ............................................. 339
Working With Cassette Tape .................................. 340
Data Storage on Floppy Diskettes ............................ 342
o The Game Ports ................................................ 343
Paddles ..................................................... 346
Light Pen ................................................... 348
o RS-232 Interface Description .................................. 348
General Outline .............................................. 348
Opening an RS-232 Channel .................................... 349
Getting Data From an RS-232 Channel .......................... 352
Sending Data to an RS-232 Channel ............................ 353
Closing an RS-232 Data Channel ............................... 354
Sample BASIC Programs ........................................ 356
vi
~
Receiver/Transmitter Buffer Base Location Pointers ........... 357
Zero-Page Memory Locations and Usage
for RS-232 System Interface ................................ 358
Nonzero-Page Memory Locations and Usage
for RS-232 System Interface ................................ 358
o The User Port ................................................. 359
Port Pin Description ........................................ 359
o The Serial Bus ................................................ 362
Serial Bus Pinouts .......................................... 363
o The Expansion Port ............................................ 366
o Z-80 Microprocessor Cartridge ................................. 368
Using Commodore CP/M (R) .................................... 369
Running Commodore CP/M (R) .................................. 369
APPENDICES ......................................................... 373
A. Abbreviations for BASIC Keywords ............................ 374
B. Screen Display Codes ........................................ 376
C. ASCII and CHR$ Codes ........................................ 379
D. Screen and Color Memory Maps ................................ 382
E. Music Note Values ........................................... 384
F. Bibliography ................................................ 388
G. VIC Chip Register Map ....................................... 391
H. Deriving Mathematical Functions ............................. 394
I. Pinouts for Input/Output Devices ............................ 395
J. Converting Standard BASIC Programs to
Commodore 64 BASIC ........................................ 398
K. Error Messages .............................................. 400
L. 6510 Microprocessor Chip Specifications ..................... 402
M. 6526 Complex Interface Adapter (CIA)
Chip Specifications ....................................... 419
N. 6566/6567 (VIC-II) Chip Specifications ...................... 436
0. 6581 Sound Interface Device (SID) Chip Specifications ....... 457
P. Glossary .................................................... 482
INDEX .............................................................. 483
COMMODORE 64 QUICK REFERENCE CARD .................................. 487
SCHEMATIC DIAGRAM OF THE COMMODORE 64 .............................. 491
vii
~~
INTRODUCTION
The COMMODORE 64 PROGRAMMER'S REFERENCE GUIDE has been developed as a
working tool and reference source for those of you who want to maximize
your use of the built-in capabilities of your COMMODORE 64. This manual
contains the information you need for your programs, from the simplest
example all the way to the most complex. The PROGRAMMER'S REFERENCE GUIDE
is designed so that everyone from the beginning BASIC programmer to the
professional experienced in 6502 machine language can get information to
develop his or her own creative programs. At the same time this book
shows you how clever your COMMODORE 64 really is.
This REFERENCE GUIDE is not designed to teach the BASIC programming
language or the 6502 machine language. There is, however, an extensive
glossary of terms and a "semi-tutorial" approach to many of the sections
in the book. If you don't already have a working knowledge of BASIC and
how to use it to program, we suggest that you study the COMMODORE 64
USER'S GUIDE that came with your computer. The USER'S GUIDE gives you an
easy to read introduction to the BASIC programming language. If you still
have difficulty understanding how to use BASIC then turn to the back of
this book (or Appendix N in the USER'S GUIDE) and check out the
Bibliography.
The COMMODORE 64 PROGRAMMER'S REFERENCE GUIDE is just that; a
reference. Like most reference books, your ability to apply the
information creatively really depends on how much knowledge you have
about the subject. In other words if you are a novice programmer you will
not be able to use all the facts and figures in this book until you
expand your current programming knowledge.
ix
~
What you can do with this book is to find a considerable amount of
valuable programming reference information written in easy to read,
plain English with the programmer's jargon explained. On the other hand
the programming professional will find all the information needed to use
the capabilities of the COMMODORE 64 effectively.
WHAT'S INCLUDED?
o Our complete "BASIC dictionary" includes Commodore BASIC language
commands, statements and functions listed in alphabetical order.
We've created a "quick list" which contains all the words and their
abbreviations. This is followed by a section containing a more
detailed definition of each word along with sample BASIC programs
to illustrate how they work.
o If you need an introduction to using machine language with BASIC
programs our layman's overview will get you started.
o A powerful feature of all Commodore computers is called the KERNAL.
It helps insure that the programs you write today can also be used
on your Commodore computer of tomorrow.
o The Input/Output Programming section gives you the opportunity to
use your computer to the limit. It describes how to hook-up and use
everything from lightpens and joysticks to disk drives, printers,
and telecommunication devices called modems.
o You can explore the world of SPRITES, programmable characters, and
high resolution graphics for the most detailed and advanced animated
pictures in the microcomputer industry.
o You can also enter the world of music synthesis and create your own
songs and sound effects with the best built-in synthesizer available
in any personal computer.
o If you're an experienced programmer, the soft load language section
gives you information about the COMMODORE 64's ability to run CP/M*
and high level languages. This is in addition to BASIC.
Think of your COMMODORE 64 PROGRAMMER'S REFERENCE GUIDE as a useful
tool to help you and you will enjoy the -hours of programming ahead
of you.
-----------
* CP/M is a registered trademark of Digital Research, Inc.
x INTRODUCTION
~
HOW TO USE THIS REFERENCE GUIDE
Throughout this manual certain conventional notations are used to de-
scribe the syntax (programming sentence structure) of BASIC commands or
statements and to show both the required and optional parts of each BASIC
keyword. The rules to use for interpreting statement syntax are as
follows:
1. BASIC keywords are shown in capital letters. They must appear where
shown in the statement, entered and spelled exactly as shown.
2. Items shown within quotation marks (" ") indicate variable data
which you must put in. Both the quotation marks and the data inside
the quotes must appear where shown in each statement.
3. Items inside the square brackets ([ ]) indicate an optional state-
ment parameter. A parameter is a limitation or additional qualifier
for your statements. If you use an optional parameter you must
supply the data for that optional parameter. In addition, ellipses
(...) show that an optional item can be repeated as many times as
a programming line allows.
4. If an item in the square brackets ([ ]) is UNDERLINED, that means
that you MUST use those certain characters in the optional para-
meters, and they also have to be spelled exactly as shown.
5. Items inside angle brackets (< >) indicate variable data which you
provide. While the slash (/) indicates that you must make a choice
between two mutually exclusive options.
EXAMPLE OF SYNTAX FORMAT:
OPEN <file-num>,<device>[,<address>],["<drive>:<filename>][,<mode>]"
EXAMPLES OF ACTUAL STATEMENTS:
10 OPEN 2,8,6,"0:STOCK FOLIO,S,W"
20 OPEN 1,1,2,"CHECKBOOK"
30 OPEN 3,4
When you actually apply the syntax conventions in a practical situa-
tion, the sequence of parameters in your statements might not be exactly
the same as the sequence shown in syntax examples. The examples are not
meant to show every possible sequence. They are intended to present all
required and optional parameters.
INTRODUCTION xi
~
Programming examples in this book are shown with blanks separating
words and operators for the sake of readability. Normally though, BASIC
doesn't require blanks between words unless leaving them out would give
you an ambiguous or incorrect syntax.
Shown below are some examples and descriptions of the symbols used for
various statement parameters in the following chapters. The list is not
meant to show every possibility, but to give you a better understanding
as to how syntax examples are presented.
SYMBOL EXAMPLE DESCRIPTION
<file-num> 50 A logical file number
<device> 4 A hardware device number
<address> 15 A serial bus secondary
device address number
<drive> 0 A physical disk drive number
<file-name> "TEST.DATA" The name of a data or program file
<constant> "ABCDEFG" Literal data supplied by
the programmer
<variable> X145 Any BASIC data variable name or
constant
<string> AB$ Use of a string type variable required
<number> 12345 Use of a numeric type variable
required
<line-number> 1000 An actual program line number
<numeric> 1.5E4 An integer or floating-point variable
COMMODORE 64 APPLICATIONS GUIDE
When you first thought about buying a computer you probably asked
yourself, "Now that I can afford to buy a computer, what can I do with
it once I get one?"
The great thing about your COMMODORE 64 is that you can make it do what
YOU want it to do! You can make it calculate and keep track of home and
business budget needs. You can use it for word processing. You can make
it play arcade-style action games. You can make it sing. You can even
create your own animated cartoons, and more. The best part of owning a
COMMODORE 64 is that even if it did only one of the things listed below
it would be well worth the price you paid for it. But the 64 is a
complete computer and it does do EVERYTHING listed and then some!
xii INTRODUCTION
~
By the way, in addition to everything here you can pick up a lot of
other creative and practical ideas by signing up with a local Commodore
Users' Club, subscribing to the COMMODORE and POWER/PLAY magazines, and
joining the COMMODORE INFORMATION NETWORK on CompuServe(TM)
APPLICATION COMMENTS/REQUIREMENTS
ACTION PACKED You can get real Bally Midway arcade games GAMES
like Omega Race, Gorf and Wizard of War, as well
as "play and learn" games like Math Teacher 1,
Home Babysitter and Commodore Artist.
ADVERTISING & Hook your COMMODORE 64 to a TV, put it in
MERCHANDISING a store window with a flashing, animated, and
musical message and you've got a great point of
purchase store display.
ANIMATION Commodore's Sprite Graphics allow you to create
real cartoons with 8 different levels so that
shapes can move in front of or behind each
other.
BABYSITTING The COMMODORE 64 HOME BABYSITTER cartridge can
keep your youngest child occupied for hours and
teach alphabet/ keyboard recognition at the same
time. It also teaches special learning concepts
and relationships.
BASIC PROGRAMMING Your COMMODORE 64 USER'S GUIDE and the TEACH
YOURSELF PROGRAMMING series of books and tapes
offer an excellent starting point.
BUSINESS The COMMODORE 64 offers the "Easy" series
SPREADSHEET of business aids including the most powerful
word processor and largest spreadsheet
available for any personal computer.
COMMUNICATION Enter the fascinating world of computer "net-
working." If you hook a VICMODEM to your
COMMODORE 64 you can communicate with other
computer owners all around the world.
INTRODUCTION xiii
~
Not only that, if you join the COMMODORE
INFORMATION NETWORK on CompuServe(TM) you can
get the latest news and updates on all Commodore
products, financial information, shop at home
services, you can even play games with the
friends you make through the information systems
you join.
COMPOSING SONGS The COMMODORE 64 is equipped with the most
sophisticated built-in music synthesizer
available on any computer. It has three com-
pletely programmable voices, nine full music
octaves, and four controllable waveforms.
Look for Commodore Music Cartridges and
Commodore Music books to help you create or
reproduce all kinds of music and sound effects.
CP/M* Commodore offers a CP/M* add-on and access to
software through an easy-to-load cartridge.
DEXTERITY TRAINING Hand/Eye coordination and manual dexterity
are aided by several Commodore games...
including "Jupiter lander" and night driving
simulation.
EDUCATION While working with a computer is an education in
itself, The COMMODORE Educational Resource Book
contains general information on the educational
uses of computers. We also have a variety of
learning cartridges designed to teach everything
from music to math and art to astronomy.
FOREIGN LANGUAGE The COMMODORE 64 programmable character set
lets you replace the standard character set
with user defined foreign language characters.
GRAPHICS AND ART In addition to the Sprite Graphics mentioned
above, the COMMODORE 64 offers high-resolution,
multi-color graphics plotting, programmable
-----------
* CP/M is a Registered trademark of Digital Research, Inc.
xiv INTRODUCTION
~
characters, and combinations of all the
different graphics and character display modes.
INSTRUMENT Your COMMODORE 64 has a serial port, RS-232 port
CONTROL and a user port for use with a variety of special
industrial applications. An IEEE/488 cartridge is
also available as an optional extra.
JOURNALS AND The COMMODORE 64 will soon offer an exceptional
CREATIVE WRITING wordprocessing system that matches or exceeds
the qualities and flexibilities of most "high-
priced" wordprocessors available. Of course you
can save the information on either a 1541 Disk
Drive or a Datassette TM recorder and have it
printed out using a VIC-PRINTER or PLOTTER.
LIGHTPEN CONTROL Applications requiring the use of a lightpen
can be performed by any lightpen that will fit
the COMMODORE 64 game port connector.
MACHINE CODE Your COMMODORE 64 PROGRAMMER'S REFERENCE GUIDE
PROGRAMMING includes a machine language section, as well as
a BASIC to machine code interface section.
There's even a bibliography available for more
in-depth study.
PAYROLL & FORMS The COMMODORE 64 can be programmed to handle
PRINTOUT a variety of entry-type business applications.
Upper/lower case letters combined with C64
"business form" graphics make it easy for you
to design forms which can then be printed on
your printer.
PRINTING The COMMODORE 64 interfaces with a variety of
dot matrix and letter quality printers as well
as plotters.
RECIPES You can store your favorite recipes on your
COMMODORE 64 and its disk or cassette storage
unit, and end the need for messy recipe cards
that often get lost when you need them most.
INTRODUCTION xv
~
SIMULATIONS Computer simulations let you conduct dangerous
or expensive experiments at minimum risk and
cost.
SPORTS DATA The Source (TM) and CompuServe (TM) both offer
sports information which you can get using
your COMMODORE 64 and a VICMODEM.
STOCK QUOTES With a VICMODEM and a subscription to any of the
appropriate network services, your COMMODORE 64
becomes your own private stock ticker.
These are just a few of the many applications for you and your
COMMODORE 64. As you can see, for work or play, at home, in school
or the office, your COMMODORE 64 gives you a practical solution for
just about any need.
Commodore wants you to know that our support for users only STARTS
with your purchase of a Commodore computer. That's why we've created
two publications with Commodore information from around the world, and
a "two-way" computer information network with valuable input for users
in the U.S. and Canada from coast to coast.
In addition, we wholeheartedly encourage and support the growth of
Commodore Users' Clubs around the world. They are an excellent source
of information for every Commodore computer owner from the beginner
to the most advanced. The magazines and network, which are more fully
described below, have the most up-to-date information about how to get
involved with the Users' Club in your area.
Finally, your local Commodore dealer is a useful source of Commodore
support and information.
POWER/PLAY
The Home Computer Magazine
When it comes to entertainment, learning at home and practical home
applications, POWER/PLAY is THE prime source of information for Com-
modore home users. Find out where your nearest user clubs are and
what they're doing, learn about software, games, programming techniques,
telecommunications, and new products. POWER/PLAY is your personal
connection to other Commodore users, outside software and hardware
developers, and to Commodore itself. Published quarterly. Only $10.00
for a year of home computing excitement.
xvi INTRODUCTION
~
COMMODORE
The Microcomputer Magazine
Widely read by educators, businessmen and students, as well as home
computerists, COMMODORE Magazine is our main vehicle for sharing
exclusive information on the more technical use of Commodore systems.
Regular departments cover business, science and education, programming
tips, "excerpts from a technical notebook," and many other features of
interest to anyone who uses or is thinking about purchasing Commodore
equipment for business, scientific or educational applications.
COMMODORE is the ideal complement to POWER/PLAY. Published bimonthly.
Subscription price: $15.00 per year.
AND FOR EVEN MORE INFORMATION...
...DIAL UP OUR PAPERLESS USER MAGAZINE
COMMODORE INFORMATION NETWORK
The magazine of the future is here. To supplement and enhance your
subscription to POWER/PLAY and COMMODORE magazines, the COMMODORE
INFORMATION NETWORK - our "paperless magazine" - is available now over
the telephone using your Commodore computer and modem.
Join our computer club, get help with a computing problem, "talk" to
other Commodore friends, or get up-to-the-minute information on new
products, software and educational resources. Soon you will even be
able to save yourself the trouble of typing in the program listings you
find in POWER/PLAY or COMMODORE by downloading direct from the
Information Network (a new user service planned for early 1983). The
best part is that most of the answers are there before you even ask the
questions. (How's that for service?)
To call our electronic magazine you need only a modem and a sub-
scription to CompuServe TM, one of the nation's largest telecommunica-
tions networks. (To make it easy for you Commodore includes a FREE year's
subscription to CompuServe TM in each VICMODEM package.) Just dial your
local number for the CompuServe (TM) data bank and connect your phone to
the modem. When the CompuServe (TM) video text appears on your screen
type G CBM on your computer keyboard. When the COMMODORE INFORMATION
NETWORK'S table of contents, or "menu," appears on your screen choose
from one of our sixteen departments, make yourself comfortable, and enjoy
the paperless magazine other magazines are writing about.
INTRODUCTION xvii
~
For more information, visit your Commodore dealer or contact Com-
puserve(TM) customer service at 800-848-8990 (in Ohio, 614-457-8600).
COMMODORE INFORMATION NETWORK
+-----------------------------------+-----------------------------------+
| Main Menu Description | Commodore Dealers |
| Direct Access Codes | Educational Resources |
| Special Commands | User Groups |
| User Questions | Descriptions |
| Public Bulletin Board | Questions and Answers |
| Magazines and Newsletters | Software Tips |
| Products Announced | Technical Tips |
| Commodore News Direct | Directory Descriptions |
+-----------------------------------+-----------------------------------+
xviii INTRODUCTION
~
CHAPTER 1
BASIC
PROGRAMMING
RULES
o Introduction
o Screen Display Codes (BASIC
Character Set)
o Programming Numbers and
variables
o Expressions and Operators
o Programming Techniques
1
~
INTRODUCTION
This chapter talks about how BASIC stores and manipulates data. The
topics include:
1) A brief mention of the operating system components and functions
as well as the character set used in the Commodore 64.
2) The formation of constants and variables. What types of variables
there are. And how constants and variables are stored in memory.
3) The rules for arithmetic calculations, relationship tests, string
handling, and logical operations. Also included are the rules for
forming expressions, and the data conversions necessary when you're
using BASIC with mixed data types.
SCREEN DISPLAY CODES (BASIC CHARACTER SET)
THE OPERATING SYSTEM (OS)
The Operating System is contained in the Read Only Memory (ROM) chips
and is a combination of three separate, but interrelated, program
modules.
1) The BASIC Interpreter
2) The KERNAL
3) The Screen Editor
1) The BASIC Interpreter is responsible for analysing BASIC statement
syntax and for performing the required calculations and/or data
manipulation. The BASIC Interpreter has a vocabulary of 65
"keywords" which have special meanings. The upper and lower case
alphabet and the digits 0-9 are used to make both keywords and
variable names. Certain punctuation characters and special symbols
also have meanings for the Interpreter. Table 1-1 lists the special
characters and their uses.
2) The KERNAL handles most of the interrupt level processing in the
system (for details on interrupt level processing, see Chapter 5).
The KERNAL also does the actual input and output of data.
3) The Screen Editor controls the output to the video screen (tele-
vision set) and the editing of BASIC program text. In addition, the
Screen Editor intercepts keyboard input so that it can decide
whether the characters put in should be acted upon immediately, or
passed on to the BASIC Interpreter.
2 BASIC PROGRAMMING RULES
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Table 1 - 1. CBM BASIC Character Set
+-------------+---------------------------------------------------------+
| CHARACTER | NAME and DESCRIPTION |
+-------------+---------------------------------------------------------+
| | BLANK - separates keywords and variable names |
| ; | SEMI-COLON - used in variable lists to format output |
| = | EQUAL SIGN - value assignment and relationship testing |
| + | PLUS SIGN - arithmetic addition or string concatenation |
| | (concatenation: linking together in a chain) |
| - | MINUS SIGN - arithmetic subtraction, unary minus |
| * | ASTERISK - arithmetic multiplication |
| / | SLASH - arithmetic division |
| ^ | UP ARROW - arithmetic exponentiation |
| ( | LEFT PARENTHESIS - expression evaluation and functions |
| ) | RIGHT PARENTHESIS - expression evaluation and functions |
| % | PERCENT - declares variable name as an integer |
| # | NUMBER - comes before logical file number in input/ |
| | output statements |
| $ | DOLLAR SIGN - declares variable name as a string |
| , | COMMA - used in variable lists to format output; also |
| | separates command parameters |
| . | PERIOD - decimal point in floating point constants |
| " | QUOTATION MARK - encloses string constants |
| : | COLON - separates multiple BASIC statements in a line |
| ? | QUESTION MARK - abbreviation for the keyword PRINT |
| < | LESS THAN - used in relationship tests |
| > | GREATER THAN - used in relationship tests |
| {pi} | PI - the numeric constant 3.141592654 |
+-------------+---------------------------------------------------------+
The Operating System gives you two modes of BASIC operation:
1) DIRECT Mode
2) PROGRAM Mode
1) When you're using the DIRECT mode, BASIC statements don't have
line numbers in front of the statement. They are executed whenever
the <RETURN> key is pressed.
2) The PROGRAM mode is the one you use for running programs.
BASIC PROGRAMMING RULES 3
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When using the PROGRAM mode, all of your BASIC statements must have
line numbers in front of them. You can have more than one BASIC
statement in a line of your program, but the number of statements is
limited by the fact that you can only put 80 characters on a logical
screen line. This means that if you are going to go over the 80
character limit you have to put the entire BASIC statement that
doesn't fit on a new line with a new line number.
Always type NEW and hit <RETURN> before starting a new program.
The Commodore 64 has two complete character sets that you can use
either from the keyboard or in your programs.
In SET 1, the upper case alphabet and the numbers 0-9 are available
without pressing the <SHIFT> key. If you hold down the <SHIFT> key
while typing, the graphics characters on the RIGHT side of the front of
the keys are used. If you hold down the <C=> key while typing, the
graphics characters on the LEFT side of the front of the key are used.
Holding down the <SHIFT> key while typing any character that doesn't
have graphic symbols on the front of the key gives you the symbol on the
top most part of the key.
In SET 2, the lower case alphabet and the numbers 0-9 are available
without pressing the <SHIFT> key. The upper case alphabet is available
when you hold down the <SHIFT> key while typing. Again, the graphic
symbols on the LEFT side of the front of the keys are displayed by press-
ing the <C=> key, while the symbols on the top most part of any key
without graphics characters are selected when you hold down the <SHIFT>
key while typing.
To switch from one character set to the other press the <C=> and
the <SHIFT> keys together.
PROGRAMMING NUMBERS AND VARIABLES
INTEGER, FLOATING-POINT AND STRING CONSTANTS
Constants are the data values that you put in your BASIC statements.
BASIC uses these values to represent data during statement execution.
CBM BASIC can recognize and manipulate three types of constants:
1) INTEGER NUMBERS
2) FLOATING-POINT NUMBERS
3) STRINGS
4 BASIC PROGRAMMING RULES
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Integer constants are whole numbers (numbers without decimal points).
Integer constants must be between -32768 and +32767. Integer constants
do not have decimal points or commas between digits. If the plus (+) sign
is left out, the constant is assumed to be a positive number. Zeros
coming before a constant are ignored and shouldn't be used since they
waste memory and slow down your program. However, they won't cause an
error. Integers are stored in memory as two-byte binary numbers. Some
examples of integer constants are:
-12
8765
-32768
+44
0
-32767
+-----------------------------------------------------------------------+
| NOTE: Do NOT put commas inside any number. For example, always type |
| 32,000 as 32000. If you put a comma in the middle of a number you |
| will get the BASIC error message ?SYNTAX ERROR. |
+-----------------------------------------------------------------------+
Floating-point constants are positive or negative numbers and can
contain fractions. Fractional parts of a number may be shown using a
decimal point. Once again remember that commas are NOT used between
numbers. If the plus sign (+) is left off the front of a number, the
Commodore 64 assumes that the number is positive. If you leave off the
decimal point the computer will assume that it follows the last digit of
the number. And as with integers, zeros that come before a constant
are ignored. Floating-point constants can be used in two ways:
1) SIMPLE NUMBER
2) SCIENTIFIC NOTATION
Floating-point constants will show you up to nine digits on your
screen. These digits can represent values between -999999999. and
+999999999. If you enter more than nine digits the number will be
rounded based on the tenth digit. if the tenth digit is greater than or
equal to 5 the number will be rounded upward. Less than 5 the number
be rounded downward. This could be important to the final totals of
some numbers you may want to work with.
Floating-point numbers are stored (using five bytes of memory) and
are manipulated in calculations with ten places of accuracy. However,
BASIC PROGRAMMING RULES 5
~
the numbers are rounded to nine digits when results are printed. Some
examples of simple floating-point numbers are:
1.23 .7777777
-.998877 -333.
+3.1459 .01
Numbers smaller than .01 or larger than 999999999. will be printed in
scientific notation. In scientific notation a floating-point constant is
made up of three parts:
1) THE MANTISSA
2) THE LETTER E
3) THE EXPONENT
The mantissa is a simple floating-point number. The letter E is used to
tell you that you're seeing the number in exponential form. In other
words E represents * 10 (eg., 3E3 = 3*10^3 = 3000). And the exponent is
what multiplication power of 10 the number is raised to.
Both the mantissa and the exponent are signed (+ or -) numbers. The
exponent's range is from -39 to +38 and it indicates the number of places
that the actual decimal point in the mantissa would be moved to the left
(-) or right (+) if the value of the constant were represented as a
simple number.
There is a limit to the size of floating-point numbers that BASIC can
handle, even in scientific notation: the largest number is
+1.70141183E+38 and calculations which would result in a larger number
will display the BASIC error message ?OVERFLOW ERROR. The smallest
floating-point number is +2.93873588E-39 and calculations which result
in a smaller value give you zero as an answer and NO error message. Some
examples of floating-point numbers in scientific notation (and their
decimal values) are:
235.988E-3 (.235988)
2359E6 (2359000000.)
-7.09E-12 (-.00000000000709)
-3.14159E+5 (-314159.)
String constants are groups of alphanumeric information like letters,
numbers and symbols. When you enter a string from the keyboard, it
can have any length up to the space available in an 80-character line
6 BASIC PROGRAMMING RULES
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(that is, any character spaces NOT taken up by the line number and other
required parts of the statement).
A string constant can contain blanks, letters, numbers, punctuation
and color or cursor control characters in any combination. You can even
put commas between numbers. The only character which cannot be included
in a string is the double quote mark ("). This is because the double
quote mark is used to define the beginning and end of the string.
A string can also have a null value-which means that it can contain no
character data. You can leave the ending quote mark off of a string if
it's the last item on a line or if it's followed by a colon (:). Some
examples of string constants are:
"" ( a null string)
"HELLO"
"$25,000.00"
"NUMBER OF EMPLOYEES"
+-----------------------------------------------------------------------+
| NOTE: Us CHR$(34) to include quotes (") in strings. |
+-----------------------------------------------------------------------+
INTEGER, FLOATING-POINT AND STRING VARIABLES
Variables are names that represent data values used in your BASIC
statements. The value represented by a variable can be assigned by
setting it equal to a constant, or it can be the result of calculations
in the program. Variable data, like constants, can be integers, floating-
point numbers, or strings. If you refer to a variable name in a program
before a value has been assigned, the BASIC Interpreter will auto-
matically create the variable with a value of zero if it's an integer or
floating-point number. Or it will create a variable with a null value if
you're using strings.
Variable names can be any length but only the first two characters are
considered significant in CBM BASIC. This means that all names used for
variables must NOT have the same first two characters. Variable names may
NOT be the same as BASIC keywords and they may NOT contain keywords in
the middle of variable names. Keywords include all BASIC commands, state-
ments, function names and logical operator names. If you accidentally use
a keyword in the middle of a variable name, the BASIC error message
?SYNTAX ERROR will show up on your screen.
The characters used to form variable names are the alphabet and the
numbers 0-9. The first character of the name must be a letter. Data
BASIC PROGRAMMING RULES 7
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type declaration characters (%) and ($) can be used as the last char-
acter of the name. The percent sign declares the variable to be an
integer and the dollar sign ($) declares a string variable. If no type
declaration character is used the Interpreter will assume that the vari-
able is a floating-point. Some examples of variable names, value as-
signments and data types are:
A$="GROSS SALES" (string variable)
MTH$="JAN"+A$ (string variable)
K%=5 (integer variable)
CNT%=CNT%+1 (integer variable)
FP=12.5 (floating-point variable)
SUM=FP*CNT% (floating-point variable)
INTEGER, FLOATING-POINT AND STRING ARRAYS
An array is a table (or list) of associated data items referred to by
a single variable name. In other words, an array is a sequence of related
variables. A table of numbers can be seen as an array, for example.
The individual numbers within the table become "elements" of the array.
Arrays are a useful shorthand way of describing a large number of
related variables. Take a table of numbers for instance. Let's say that
the table has 10 rows of numbers with 20 numbers in each row. That makes
total of 200 numbers in the table. Without a single array name to call
on you would have to assign a unique name to each value in the table. But
because you can use arrays you only need one name for the array and all
the elements in the array are identified by their individual locations
within the array.
Array names can be integers, floating-points or string data types and
all elements in the array have the same data type as the array name.
Arrays can have a single dimension (as in a simple list) or they can have
multiple dimensions (imagine a grid marked in rows and columns or a
Rubik's Cube(R)). Each element of an array is uniquely identified and re-
ferred to by a subscript (or index variable) following the array name,
enclosed within parentheses ( ).
The maximum number of dimensions an array can have in theory is 255
and the number of elements in each dimension is limited to 32767. But
for practical purposes array sizes are limited by the memory space
available to hold their data and/or the 80 character logical screen line.
If an array has only one dimension and its subscript value will never
8 BASIC PROGRAMMING RULES
~
exceed 1 0 (1 I items: 0 thru 1 0) then the array will be created by the
Interpreter and filled with zeros (or nulls if string type) the first
time any element of the array is referred to, otherwise the BASIC DIM
statement must be used to define the shape and size of the array. The
amount of memory required to store an array can be determined as follows:
5 bytes for the array name
+ 2 bytes for each dimension of the array
+ 2 bytes per element for integers
OR + 5 bytes per element for floating-point
OR + 3 bytes per element for strings
AND + 1 byte per character in each string element
Subscripts can be integer constants, variables, or an arithmetic ex-
pression which gives an integer result. Separate subscripts, with com-
mas between them, are required for each dimension of an array. Sub-
scripts can have values from zero up to the number of elements in the
respective dimensions of the array. Values outside that range will cause
the BASIC error message ?BAD SUBSCRIPT. Some examples of array names,
value assignments and data types are:
A$(0)="GROSS SALES" (string array)
MTH$(K%)="JAN" (string array)
G2%(X)=5 (integer array)
CNT%(G2%(X))=CNT%(1)-2 (integer array)
FP(12*K%)=24.8 (floating-point array)
SUM(CNT%(1))=FP^K% (floating-point array)
A(5)=0 (sets the 5th element in the 1 dimensional
array called "A" equal to 0)
B(5,6)=0 (sets the element in row position 5 and column position 6
in the 2 dimensional array called "B" equal to 0)
C(1,2,3)=0 (sets the element in row position 1, column position 2,
and depth position 3 in the 3 dimensional array called
"C" equal to 0)
EXPRESSIONS AND OPERATORS
Expressions are formed using constants, variables and/or arrays. An
expression can be a single constant, simple variable, or an array vari-
BASIC PROGRAMMING RULES 9
~
able of any type. It can also be a combination of constants and variables
with arithmetic, relational or logical operators designed to produce a
ingle value. How operators work is explained below. Expressions can be
separated into two classes:
1) ARITHMETIC
2) STRING
Expressions are normally thought of as having two or more data items
called operands. Each operand is separated by a single operator to
produce the desired result. This is usually done by assigning the value
of the expression to a variable name. All of the examples of constants
and variables that you've seen so for, were also examples of expressions.
An operator is a special symbol the BASIC Interpreter in your Commodore
64 recognizes as representing an operation to be performed on the
variables or constant data. One or more operators, combined with one or
more variables and/or constants form an expression. Arithmetic,
relational and logical operators are recognized by Commodore 64 BASIC.
ARITHMETIC EXPRESSIONS
Arithmetic expressions, when solved, will give an integer or floating-
point value. The arithmetic operators (+, -, *, /, ^) are used to perform
addition, subtraction, multiplication, division and exponentiation opera-
tions respectively.
ARITHMETIC OPERATIONS
An arithmetic operator defines an arithmetic operation which is per-
formed on the two operands on either side of the operator. Arithmetic
operations are performed using floating-point numbers. Integers are
converted to floating-point numbers before an arithmetic operation is
performed. The result is converted back to an integer if it is assigned
to an integer variable name.
ADDITION (+): The plus sign (+) specifies that the operand on the
right is added to the operand on the left.
10 BASIC PROGRAMMING RULES
~
EXAMPLES:
2+2
A+B+C
X%+1
BR+10E-2
SUBTRACTION (-): The minus sign (-) specifies that the operand on the
right is subtracted from the operand on the left.
EXAMPLES:
4-1
100-64
A-B
55-142
The minus can also be used as a unary minus. That means that it is the
minus sign in front of a negative number. This is equal to subtracting
the number from zero (0).
EXAMPLES:
-5
-9E4
-B
4-(-2) same as 4+2
MULTIPLICATION (*): An asterisk (*) specifies that the operand on the
left is multiplied by the operand on the right.
EXAMPLES:
100*2
50*0
A*X1
R%*14
DIVISION (/): The slash (/) specifies that the operand on the left is
divided by the operand on the right.
EXAMPLES:
10/2
6400/4
A/B
4E2/XR
BASIC PROGRAMMING RULES 11
~
EXPONENTIATION The up arrow (^) specifies that the operand on the
left is raised to the power specified by the operand on the right (the
exponent). If the operand on the right is a 2, the number on the left is
squared; if the exponent is a 3, the number on the left is cubed, etc.
The exponent can be any number so long as the result of the operation
gives a valid floating-point number.
EXAMPLES:
2^2 Equivalent to: 2*2
3^3 Equivalent to: 3*3*3
4^4 Equivalent to: 4*4*4*4
AB^CD
3^-2 Equivalent to: 1/3*1/3
RELATIONAL OPERATORS
The relational operators (<, =, >, <=, >=, <>) are primarily used
to compare the values of two operands, but they also produce an arith-
metic result. The relational operators and the logical operators (AND,
OR, and NOT), when used in comparisons, actually produce an arithmetic
true/false evaluation of an expression. If the relationship stated in
the expression is true the result is assigned an integer value of - 1
and if it's false a value of 0 is assigned. These are the relational
operators:
< LESS THAN
= EQUAL TO
> GREATER THAN
<= LESS THAN OR EQUAL TO
>= GREATER THAN OR EQUAL TO
<> NOT EQUAL TO
EXAMPLES:
1 =5-4 result true (-1)
14>66 result false (0)
15>=15 result true (-1)
Relational operators can be used to compare strings. For comparison
purposes, the letters of the alphabet have the order A<B<C<D, etc.
Strings are compared by evaluating the relationship between corre-
sponding characters from left to right (see String Operations).
12 BASIC PROGRAMMING RULES
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EXAMPLES:
"A" < "B" result true (-1)
"X" = "YY" result false (0)
BB$ <> CC$
Numeric data items can only be compared (or assigned) to other numeric
items. The same is true when comparing strings, otherwise the BASIC error
message ?TYPE MISMATCH will occur. Numeric operands are compared by first
converting the values of either or both operands from integer to
floating-point form, as necessary. Then the relationship of the floating-
point values is evaluated to give a true/false result.
At the end of all comparisons, you get an integer no matter what data
type the operand is (even if both are strings). Because of this,
a comparison of two operands can be used as an operand in performing
calculations. The result will be - 1 or 0 and can be used as anything but
a divisor, since division by zero is illegal.
LOGICAL OPERATORS
The logical operators (AND, OR, NOT) can be used to modify the meanings
of the relational operators or to produce an arithmetic result. Logical
operators can produce results other than -1 and 0, though any nonzero
result is considered true when testing for a true/false condition.
The logical operators (sometimes called Boolean operators) can also be
used to perform logic operations on individual binary digits (bits) in
two operands. But when you're using the NOT operator, the operation is
performed only on the single operand to the right. The operands must be
in the integer range of values (-32768 to +32767) (floating-point
numbers are converted to integers) and logical operations give an integer
result.
Logical operations are performed bit-by-corresponding-bit on the two
operands. The logical AND produces a bit result of 1 only if both operand
bits are 1. The logical OR produces a bit result of I if either operand
bit is 1. The logical NOT is the opposite value of each bit as a single
operand. In other words, it's really saying, "if it's NOT 1 then it is 0.
If it's NOT 0 then it is 1."
The exclusive OR (XOR) doesn't have a logical operator but it is per-
formed as part of the WAIT statement. Exclusive OR means that if the bits
of two operands are equal then the result is 0 otherwise the result is 1.
Logical operations are defined by groups of statements which, taken
together, constitute a Boolean "truth table" as shown in Table 1-2.
BASIC PROGRAMMING RULES 13
~
Table 1-2. Boolean Truth Table
+-----------------------------------------------------------------------+
| The AND operation results in a 1 only if both bits are 1: |
| |
| 1 AND 1 = 1 |
| 0 AND 1 = 0 |
| 1 AND 0 = 0 |
| 0 AND 0 = 0 |
| |
| The OR operation results in a 1 if either bit is 1: |
| |
| 1 OR 1 = 1 |
| 0 OR 1 = 1 |
| 0 OR 0 = 1 |
| 0 OR 0 = 0 |
| |
| The NOT operation logically complements each bit: |
| |
| NOT 1 = 0 |
| NOT 0 = 1 |
| |
| The exclusive OR (XOR) is part of the WAIT statement! |
| |
| 1 XOR 1 = 0 |
| 1 XOR 0 = 1 |
| 0 XOR 1 = 1 |
| 0 XOR 0 = 0 |
+-----------------------------------------------------------------------+
The logical operators AND, OR and NOT specify a Boolean arithmetic
operation to be performed on the two operand expressions on either side
of the operator. In the case of NOT, ONLY the operand on the RIGHT is
considered. Logical operations (or Boolean arithmetic) aren't performed
until all arithmetic and relational operations in an expression have been
completed.
EXAMPLES:
IF A=100 AND B=100 THEN 10 (if both A and B have a value
of 100 then the result is true)
A=96 AND 32: PRINT A (A = 32)
14 BASIC PROGRAMMING RULES
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IF A=100 OR B=100 THEN 20 (if A or B is 100 then the
result is true)
A=64 OR 32: PRINT A (A = 96)
IF NOT X<Y THEN 30 (if X>=Y the result is true)
X= NOT 96 (result is -97 (two's complement))
HIERARCHY OF OPERATIONS
All expressions perform the different types of operations according to
a fixed hierarchy. In other words, certain operations are performed be-
fore other operations. The normal order of operations can be modified
by enclosing two or more operands within parentheses ( ), creating a
"subexpression." The parts of an expression enclosed in parentheses will
be reduced to a single value before working on parts outside the par-
entheses.
When you use parentheses in expressions, they must be paired so that
you always have an equal number of left and right parentheses. Otherwise,
the BASIC error message ?SYNTAX ERROR will appear.
Expressions which have operands inside parentheses may themselves
be enclosed in parentheses, forming complex expressions of multiple
levels. This is called nesting. Parentheses can be nested in expressions
to a maximum depth of ten levels-ten matching sets of parentheses.
The inner-most expression has its operations performed first. Some
examples of expressions are:
A+B
C^(D+E)/2
((X-C^(D+E)/2)*10)+1
GG$>HH$
JJ$+"MORE"
K%=1 AND M<>X
K%=2 OR (A=B AND M<X)
NOT (D=E)
The BASIC Interpreter will normally perform operations on expressions
by performing arithmetic operations first, then relational operations,
and logical operations lost. Both arithmetic and logical operators have
BASIC PROGRAMMING RULES 15
~
an order of precedence (or hierarchy of operations) within themselves. On
the other hand, relational operators do not have an order of precedence
and will be performed as the expression is evaluated from left to right.
If all remaining operators in an expression have the same level of
precedence then operations happen from left to right. When performing
operations on expressions within parentheses, the normal order of pre-
cedence is maintained. The hierarchy of arithmetic and logical opera-
tions is shown in Table 1-3 from first to last in order of precedence.
Table 1-3. Hierarchy of Operations Performed on Expressions
+---------------+---------------------------------+---------------------+
| OPERATOR | DESCRIPTION | EXAMPLE |
+---------------+---------------------------------+---------------------+
| ^ | Exponentiation | BASE ^ EXP |
| | | |
| - | Negation (Unary Minus) | -A |
| | | |
| * / | Multiplication | AB * CD |
| | Division | EF / GH |
| | | |
| + - | Addition | CNT + 2 |
| | Subtraction | JK - PQ |
| | | |
| > = < | Relational Operations | A <= B |
| | | |
| NOT | Logical NOT | NOT K% |
| | (Integer Two's Complement) | |
| | | |
| AND | Logical AND | JK AND 128 |
| | | |
| OR | Logical OR | PQ OR 15 |
+---------------+---------------------------------+---------------------+
STRING OPERATIONS
Strings are compared using the same relational operators (=, <>,
<=, >=, <, >) that are used for comparing numbers. String compari-
sons are mode by taking one character at a time (left-to-right) from
each string and evaluating each character code position from the PET/
CBM character set. If the character codes are the same, the characters
are equal. If the character codes differ, the character with the lower
code number is lower in the character set. The comparison stops when
16 BASIC PROGRAMMING RULES
~
the end of either string is reached. All other things being equal, the
shorter string is considered less than the longer string. Leading or
trailing blanks ARE significant.
Regardless of the data types, at the end of all comparisons you get
an integer result. This is true even if both operands are strings.
Because of this a comparison of two string operands can be used as an
operand in performing calculations. The result will be - 1 or 0 (true or
false) and can be used as anything but a divisor since division by zero
is illegal.
STRING EXPRESSIONS
Expressions are treated as if an implied "<>0" follows them. This means
that if an expression is true then the next BASIC statements on. the same
program line are executed. If the expression is false the rest of the
line is ignored and the next line in the program is executed.
Just as with numbers, you can also perform operations on string vari-
ables. The only string arithmetic operator recognized by CBM BASIC is the
plus sign (+) which is used to perform concatenation of strings. When
strings are concatenated, the string on the right of the plus sign is
appended to the string on the left, forming a third string as a result.
The result can be printed immediately, used in a comparison, or assigned
to a variable name. If a string data item is compared with (or set equal
to) a numeric item, or vice-versa, the BASIC error message ?TYPE MISMATCH
will occur. Some examples of string expressions and concatenation are:
10 A$="FILE": B$="NAME"
20 NAM$=A$+B$ (gives the string: FILENAME)
30 RES$="NEW "+A$+B$ (gives the string: NEW FILENAME)
^
| +-----------------+
+-------+ Note space here.|
+-----------------+
BASIC PROGRAMMING RULES 17
~
PROGRAMMING TECHNIQUES
DATA CONVERSIONS
When necessary, the CBM BASIC Interpreter will convert a numeric
data item from an integer to floating-point. or vice-versa, according to
the following rules:
o All arithmetic and relational operations are performed in floating
point format. Integers are converted to floating-point form for
evaluation of the expression, and the result is converted back to
integer. logical operations convert their operands to integers an
return an integer result.
o If a numeric variable name of one type is set equal to a numeric
data item of a different type, the number will be converted and
stored as the data type declared in the variable name.
o When a floating-point value is converted to an integer, the frac-
tional portion is truncated (eliminated) and the integer result is
less than or equal to the floating-point value. If the result is
outside the range of +32767 thru -32768, the BASIC error message
?ILLEGAL QUANTITY will occur.
USING THE INPUT STATEMENT
Now that you know what variables are, let's take that information an
put it together with the INPUT statement for some practical program-
ming applications.
In our first example, you can think of a variable as a "storage com-
partment" where the Commodore 64 stores the user's response to your
prompt question. To write a program which asks the user to type in a
name, you might assign the variable N$ to the name typed in. Now
every time you PRINT N$ in your program, the Commodore 64 will
automatically PRINT the name that the user typed in.
Type the word NEW on your Commodore 64. Hit the <RETURN> key
and try this example:
10 PRINT"YOUR NAME": INPUT N$
20 PRINT"HELLO",N$
18 BASIC PROGRAMMING RULES
~
In this example you used N to remind yourself that this variable stands
for "NAME". The dollar sign ($) is used to tell the computer that you're
using a string variable. It is important to differentiate between the two
types of variables:
1) NUMERIC
2) STRING
You probably remember from the earlier sections that numeric vari-
ables are used to store number values such as 1, 100, 4000, etc. A
numeric variable can be a single letter (A), any two letters (AB), a
letter and a number (AI), or two letters and a number (AB1). You can save
memory space by using shorter variables. Another helpful hint is to use
letters and numbers for different categories in the same program (AI,
A2, A3). Also, if you want whole numbers for an answer instead of
numbers with decimal points, all you have to do is put a percent sign
(%) at the end of your variable name (AB%, AI%, etc.)
Now let's look at a few examples that use different types of variables
and expressions with the INPUT statement.
10 PRINT"ENTER A NUMBER": INPUT A
20 PRINT A
10 PRINT"ENTER A WORD": INPUT A$
20 PRINT A$
10 PRINT"ENTER A NUMBER": INPUT A
20 PRINT A "TIMES 5 EQUALS" A*5
+-----------------------------------------------------------------------+
| NOTE: Example 3 shows that MESSAGES or PROMPTS are inside the |
| quotation marks (" ") while the variables are outside. Notice, too, |
| that in line 20 the variable A was printed first, then the message |
| "TIMES 5 EQUALS", and then the calculation, multiply variable A by 5 |
| (A*5). |
+-----------------------------------------------------------------------+
Calculations are important in most programs. You have a choice of using
"actual numbers" or variables when doing calculations, but if you're
working with numbers supplied by a user you must use numeric variables.
Begin by asking the user to type in two numbers like this:
10 PRINT"TYPE 2 NUMBERS": INPUT A: INPUT B
BASIC PROGRAMMING RULES 19
~
INCOME/EXPENSE BUDGET EXAMPLE
start tok64 page20.prg
5 print"{clear}"
10 print"monthly income":input in
20 print
30 print"expense category 1":input e1$
40 print"expense amount":input e1
50 print
60 print"expense category 2":input e2$
70 print"expense amount":input e2
80 print
90 print"expense category 3":input e3$
100 print"expense amount":input e3
110 print"{clear}"
120 e=e1+e2+e3
130 ep=e/in
140 print"monthly income: $"in
150 print"total expenses: $"e
160 print"balance equals: $"in-e
170 print
180 print e1$"="(e1/e)*100"% of total expenses"
190 print e2$"="(e2/e)*100"% of total expenses"
200 print e3$"="(e3/e)*100"% of total expenses"
210 print
220 print"your expenses="ep*100"% of your total income"
230 forx=1to5000:next:print
240 print"repeat? (y or n)":input y$:if y$="y"then 5
250 print"{clear}":end
stop tok64
+-----------------------------------------------------------------------+
| NOTE:IN can NOT = 0, and E1, E2, E3 can NOT all be 0 at the same time.|
+-----------------------------------------------------------------------+
20 BASIC PROGRAMMING RULES
~
LINE-BY-LINE EXPLANATION OF
INCOME/EXPENSE BUDGET EXAMPLE
+-----------+-----------------------------------------------------------+
| Line(s) | Description |
+-----------+-----------------------------------------------------------+
| 5 | Clears the screen. |
| 10 | PRINT/INPUT statement. |
| 20 | Inserts blank line. |
| 30 | Expense Category 1 = E1$. |
| 40 | Expense Amount = E1. |
| 50 | Inserts blank line. |
| 60 | Expense Category 2 = E2. |
| 70 | Expense Amount 2 = E2. |
| 80 | Inserts blank line. |
| 90 | Expense Category 3 = E3. |
| 100 | Expense Amount 3 = E3. |
| 110 | Clears the screen. |
| 120 | Add Expense Amounts = E. |
| 130 | Calculate Expense/income%. |
| 140 | Display Income. |
| 150 | Display Total Expenses. |
| 160 | Display Incomes - Expenses. |
| 170 | Inserts blank line. |
| 180-200 | lines 180-200 calculate % each expense |
| | amount is of total expenses. |
| 210 | Inserts blank line. |
| 220 | Display E/IN %. |
| 230 | Time delay loop. |
+-----------+-----------------------------------------------------------+
Now multiply those two numbers together to create a new variable C as
shown in line 20 below:
20 C=A*B
To PRINT the result as a message type
30 PRINT A "TIMES" B "EQUALS" C
Enter these 3 lines and RUN the program. Notice that the messages are
inside the quotes while the variables are not.
BASIC PROGRAMMING RULES 21
~
Now let's say that you wanted a dollar sign ($) in front of the number
represented by variable C. The $ must be PRINTed inside quotes and in
front of variable C. To add the $ to your program hit the <RUN/STOP>
and <RESTORE> keys. Now type in line 40 as follows:
40 PRINT"$" C
Now hit <RETURN>, type RUN and hit <RETURN> again.
The dollar sign goes in quotes because the variable C only represents
a number and can't contain a $. If the number represented by C was
100 then the Commodore 64 screen would display $ 100. But, if you
tried to PRINT $C without using the quotes, you would get a ?SYNTAX
ERROR message.
One last tip about $$$: You can create a variable that represents a
dollar sign which you can then substitute for the $ when you want to use
it with numeric variables. For example:
10 Z$="$"
Now whenever you need a dollar sign you can use the string variable
Z$. Try this:
10 Z$="$": INPUT A
20 PRINT Z$A
line 10 defines the $ as a string variable called Z$, and then INPUTs a
number called A. line 20 PRINTs Z$ ($) next to A (number).
You'll probably find that it's easier to assign certain characters,
like dollar signs, to a string variable than to type "$" every time you
want to calculate dollars or other items which require "" like %.
USING THE GET STATEMENT
Most simple programs use the INPUT statement to get data from the
person operating the computer. When you're dealing with more complex
needs, like protection from typing errors, the GET statement gives you
more flexibility and your program more "intelligence." This section shows
you how to use the GET statement to add some special screen editing
features to your programs.
22 BASIC PROGRAMMING RULES
~
The Commodore 64 has a keyboard buffer that holds up to 10 characters.
This means that if the computer is busy doing some operation and it's
not reading the keyboard, you can still type in up to 10 characters,
which will be used as soon as the Commodore 64 finishes what it was
doing. To demonstrate this, type in this program on your Commodore 64:
NEW
10 TI$="000000"
20 IF TI$ < "000015" THEN 20
Now type RUN, hit <RETURN> and while the program is RUNning type in the
word HELLO.
Notice that nothing happened for about IS seconds when the program
started. Only then did the message HELLO appear on the screen.
Imagine standing in line for a movie. The first person in the line is
the first to get a ticket and leave the line. The last person in line is
last for a ticket. The GET statement acts like a ticket taker. First it
looks to see if there are any characters "in line." In other words have
any keys been typed. If the answer is yes then that character gets placed
in the appropriate variable. If no key was pressed then an empty value is
assigned to a variable,
At this point it's important to note that if you try to put more than
10 characters into the buffer at one time, all those over the 10th
character will be lost.
Since the GET statement will keep going even when no character is
typed, it is often necessary to put the GET statement into a loop so that
it will have to wait until someone hits a key or until a character is
received through your program.
Below is the recommended form for the GET statement. Type NEW to erase
your previous program.
10 GET A$: IF A$ ="" THEN 10
Notice that there is NO SPACE between the quote marks("") on this line.
This indicates an empty value and sends the program back to the GET
statement in a continuous loop until someone hits a key on the computer.
Once a key is hit the program will continue with the line following line
10. Add this line to your program:
100 PRINT A$;: GOTO 10
BASIC PROGRAMMING RULES 23
~
Now RUN the program. Notice that no cursor appears on the screen, but
any character you type will be printed in the screen. This 2-line program
can be turned into part of a screen editor program as shown below.
There are many things you can do with a screen editor. You can have
a flashing cursor. You can keep certain keys like <CLR/HOME> from
accidentally erasing the whole screen. You might even want to be able to
use your function keys to represent whole words or phrases. And speaking
of function keys, the following program lines give each function key a
special purpose. Remember this is only the beginning of a program that
you can customize for your needs.
20 IF A$ = CHR$(133) THEN POKE 53280,8: GOTO 10
30 IF A$ = CHR$(134) THEN POKE 53281,4: GOTO 10
40 IF A$ = CHR$(135) THEN A$="DEAR SIR:"+CHR$(13)
50 IF A$ = CHR$(136) THEN A$="SINCERELY,"+CHR$(13)
The CHR$ numbers in parentheses come from the CHR$ code chart in
Appendix C. The chart lists a different number for each character. The
four function keys are set up to perform the tasks represented by the
instructions that follow the word THEN in each line. By changing the
CHR$ number inside each set of parentheses you can designate different
keys. Different instructions would be performed if you changed the
information after the THEN statement.
HOW TO CRUNCH BASIC PROGRAMS
You can pack more instructions - and power - into your BASIC programs by
making each program as short as possible. This process of shortening
programs is called "crunching."
Crunching programs lets you squeeze the maximum possible number of
instructions into your program. It also helps you reduce the size of
programs which might not otherwise run in a given size; and if you're
writing a program which requires the input of data such as inventory
items, numbers or text, a short program will leave more memory space free
to hold data.
ABBREVIATING KEYWORDS
A list of keyword abbreviations is given in Appendix A. This is helpful
when you program because you can actually crowd more information on each
line using abbreviations. The most frequently used abbreviation is
24 BASIC PROGRAMMING RULES
~
the question mark (?) which is the BASIC abbreviation for the PRINT
command. However, if you LIST a program that has abbreviations, the
Commodore 64 will automatically print out the listing with the full-
length keywords. If any program line exceeds 80 characters (2 lines on
the screen) with the keywords unabbreviated, and you want to change it,
you will have to re-enter that line with the abbreviations before saving
the program. SAVEing a program incorporates the keywords without
inflating any lines because BASIC keywords are tokenized by the Commodore
64. Usually, abbreviations are added after a program is written and it
isn't going to be LISTed any more before SAVEing.
SHORTENING PROGRAM LINE NUMBERS
Most programmers start their programs at line 100 and number each fine
at intervals of 10 (i.e., 100, 110, 120). This allows extra lines of
instruction to be added (111, 112, etc.) as the program is developed.
One means of crunching the program after it is completed is to change
the fine numbers to the lowest numbers possible (i.e., 1, 2, 3) because
longer line numbers take more memory than shorter numbers when referenced
by GOTO and GOSUB statements. For instance, the number 100 uses 3 bytes
of memory (one for each number) while the number I uses only 1 byte.
PUTTING MULTIPLE INSTRUCTIONS ON EACH LINE
You can put more than one instruction on each numbered line in your
program by separating them by a colon. The only limitation is that all
the instructions on each line, including colons, should not exceed the
standard 80-character line length. Here is an example of two programs,
before and after crunching:
BEFORE CRUNCHING: AFTER CRUNCHING:
10 PRINT"HELLO..."; 10 PRINT "HELLO...";:FORT=1TO500:NEXT:
20 FOR T=1 TO 500: NEXT PRINT"HELLO, AGAIN...":GOTO10
30 PRINT"HELLO, AGAIN..."
40 GOTO 10
REMOVING REM STATEMENTS
REM statements are helpful in reminding yourself-or showing other
programmers - what a particular section of a program is doing. However,
when the program is completed and ready to use, you probably
BASIC PROGRAMMING RULES 25
~
won't need those REM statements anymore and you can save quite a bit of
space by removing the REM statements. If you plan to revise or study the
program structure in the future, it's a good idea to keep a copy on file
with the REM statements intact.
USING VARIABLES
If a number, word or sentence is used repeatedly in your program it's
usually best to define those long words or numbers with a one or two
letter variable. Numbers can be defined as single letters. Words and
sentences can be defined as string variables using a letter and dollar
sign. Here's one example:
BEFORE CRUNCHING: AFTER CRUNCHING:
10 POKE 54296,15 10 V=54296:F=54273
20 POKE 54276,33 20 POKEV,15:POKE54276,33
30 POKE 54273,10 30 POKEF,10:POKEF,40:POKEF,70
40 POKE 54273,40 40 POKEV,0
50 POKE 54273,70
60 POKE 54296,0
USING READ AND DATA STATEMENTS
Large amounts of data can be typed in as one piece of data at a time,
over and over again ... or you can print the instructional part of the
program ONCE and print all the data to be handled in a long running list
called the DATA statement. This is especially good for crowding large
lists of numbers into a program.
USING ARRAYS AND MATRICES
Arrays and matrices are similar to DATA statements in that long amounts
of data can be handled as a list, with the data handling portion of the
program drawing from that list, in sequence. Arrays differ in that the
list can be multi-dimensional
ELIMINATING SPACES
One of the easiest ways to reduce the size of your program is to
eliminate all the spaces. Although we often include spaces in sample
26 BASIC PROGRAMMING RULES
~
programs to provide clarity, you actually don't need any spaces in your
program and will save space if you eliminate them.
USING GOSUB ROUTINES
If you use a particular line or instruction over and over, it might be
wise to GOSUB to the line from several places in your program, rather
than write the whole line or instruction every time you use it.
USING TAB AND SPC
Instead of PRINTing several cursor commands to position a character
on the screen, it is often more economical to use the TAB and SPC in-
structions to position words or characters on the screen.
BASIC PROGRAMMING RULES 27
~~
CHAPTER 2
BASIC LANGUAGE
VOCABULARY
o Introduction
o BASIC Keywords, Abbreviations,
and Function Types
o Description of BASIC Keywords
(Alphabetical)
o The Commodore 64 Keyboard and
Features
o Screen Editor
~
INTRODUCTION
This chapter explains CBM BASIC Language keywords. First we give you an
easy to read list of keywords, their abbreviations and what each letter
looks like on the screen. Then we explain how the syntax and operation of
each keyword works in detail, and examples are shown to give you an idea
as to how to use them in your programs.
As a convenience, Commodore 64 BASIC allows you to abbreviate most
keywords. Abbreviations are entered by typing enough letters of the
keyword to distinguish it from all other keywords, with the last letter
or graphics entered holding down the <SHIFT> key.
Abbreviations do NOT save any memory when they're used in programs,
because all keywords are reduced to single-character "tokens" by the
BASIC Interpreter. When a program containing abbreviations is listed, all
keywords appear in their fully spelled form. You can use abbreviations to
put more statements onto a program line even if they won't fit onto the
80-character logical screen line. The Screen Editor works on an 80-
character line. This means that if you use abbreviations on any line that
goes over 80 characters, you will NOT be able to edit that line when
LISTed. Instead, what you'll have to do is (1) retype the entire line
including all abbreviations, or (2) break the single line of code into
two lines, each with its own line number, etc.
A complete list of keywords, abbreviations, and their appearance on the
screen is presented in Table 2-1. They are followed by an alphabetical
description of all the statements, commands, and functions available on
your Commodore 64.
This chapter also explains the BASIC functions built into the BASIC
Language Interpreter. Built-in functions can be used in direct mode
statements or in any program, without having to define the function
further. This is NOT the case with user-defined functions. The results of
built-in BASIC functions can be used as immediate output or they can be
assigned to a variable name of an appropriate type. There are two types
of BASIC functions:
1) NUMERIC
2) STRING
Arguments of built-in functions are always enclosed in parentheses ().
The parentheses always come directly after the function keyword and NO
SPACES between the last letter of the keyword and the left parenthesis (.
30 BASIC LANGUAGE VOCABULARY
~
The type of argument needed is generally decided by the data type in
the result. Functions which return a string value as their result are
identified by having a dollar sign ($) as the last character of the
keyword. In some cases string functions contain one or more numeric
argument. Numeric functions will convert between integer and floating-
point format as needed. In the descriptions that follow, the data type of
the value returned is shown with each function name. The types of argu-
ments are also given with the statement format.
Table 2-1. COMMODORE 64 BASIC KEYWORDS
+-----------+----------------------+----------------+-------------------+
| COMMAND | ABBREVIATION | SCREEN | FUNCTION TYPE |
+-----------+----------------------+----------------+-------------------+
| | | | |
| ABS | A <SHIFT+B> | | NUMERIC |
| | | | |
| AND | A <SHIFT+N> | | |
| | | | |
| ASC | A <SHIFT+S> | | NUMERIC |
| | | | |
| ATN | A <SHIFT+T> | | NUMERIC |
| | | | |
| CHR$ | C <SHIFT+H> | | STRING |
| | | | |
| CLOSE | CL <SHIFT+O> | | |
| | | | |
| CLR | C <SHIFT+L> | | |
| | | | |
| CMD | C <SHIFT+M> | | |
| | | | |
| CONT | C <SHIFT+O> | | |
| | | | |
| COS | none | COS | NUMERIC |
| | | | |
| DATA | D <SHIFT+A> | | |
| | | | |
| DEF | D <SHIFT+E> | | |
| | | | |
| DIM | D <SHIFT+I> | | |
BASIC LANGUAGE VOCABULARY 31
~
+-----------+----------------------+----------------+-------------------+
| COMMAND | ABBREVIATION | SCREEN | FUNCTION TYPE |
+-----------+----------------------+----------------+-------------------+
| | | | |
| END | E <SHIFT+N> | | |
| | | | |
| EXP | E <SHIFT+X> | | NUMERIC |
| | | | |
| FN | none | FN | |
| | | | |
| FOR | F <SHIFT+O> | | |
| | | | |
| FRE | F <SHIFT+R> | | NUMERIC |
| | | | |
| GET# | none | GET# | |
| | | | |
| GOSUB | GO <SHIFT+S> | | |
| | | | |
| GOTO | G <SHIFT+O> | | |
| | | | |
| IF | none | IF | |
| | | | |
| INPUT | none | INPUT | |
| | | | |
| INPUT# | I <SHIFT+N> | | |
| | | | |
| INT | none | INT | NUMERIC |
| | | | |
| LEFT$ | LE <SHIFT+F> | | STRING |
| | | | |
| LEN | none | LEN | NUMERIC |
| | | | |
| LET | L <SHIFT+E> | | |
| | | | |
| LIST | L <SHIFT+I> | | |
| | | | |
| LOAD | L <SHIFT+O> | | |
| | | | |
| LOG | none | LOG | NUMERIC |
32 BASIC LANGUAGE VOCABULARY
~
+-----------+----------------------+----------------+-------------------+
| COMMAND | ABBREVIATION | SCREEN | FUNCTION TYPE |
+-----------+----------------------+----------------+-------------------+
| | | | |
| MID$ | M <SHIFT+I> | | STRING |
| | | | |
| NEW | none | NEW | |
| | | | |
| NEXT | N <SHIFT+E> | | |
| | | | |
| NOT | N <SHIFT+O> | | |
| | | | |
| ON | none | ON | |
| | | | |
| OPEN | O <SHIFT+P> | | |
| | | | |
| OR | none | OR | |
| | | | |
| PEEK | P <SHIFT+E> | | NUMERIC |
| | | | |
| POKE | P <SHIFT+O> | | |
| | | | |
| POS | none | POS | NUMERIC |
| | | | |
| PRINT | ? | ? | |
| | | | |
| PRINT# | P <SHIFT+R> | | |
| | | | |
| READ | R <SHIFT+E> | | |
| | | | |
| REM | none | REM | |
| | | | |
| RESTORE| RE <SHIFT+S> | | |
| | | | |
| RETURN | RE <SHIFT+T> | | |
| | | | |
| RIGHT$ | R <SHIFT+I> | | STRING |
| | | | |
| RND | R <SHIFT+N> | | NUMERIC |
| | | | |
| RUN | R <SHIFT+U> | | |
BASIC LANGUAGE VOCABULARY 33
~
| | | | |
| SAVE | S <SHIFT+A> | | |
| | | | |
| SGN | S <SHIFT+G> | | NUMERIC |
| | | | |
| SIN | S <SHIFT+I> | | NUMERIC |
| | | | |
| SPC( | S <SHIFT+P> | | SPECIAL |
| | | | |
| SQR | S <SHIFT+Q> | | NUMERIC |
| | | | |
| STATUS | ST | ST | NUMERIC |
| | | | |
| STEP | ST <SHIFT+E> | | |
| | | | |
| STOP | S <SHIFT+T> | | |
| | | | |
| STR$ | ST <SHIFT+R> | | STRING |
| | | | |
| SYS | S <SHIFT+Y> | | |
| | | | |
| TAB( | T <SHIFT+A> | | SPECIAL |
| | | | |
| TAN | none | TAN | NUMERIC |
| | | | |
| THEN | T <SHIFT+H> | | |
| | | | |
| TIME | TI | TI | NUMERIC |
| | | | |
| TIME$ | TI$ | TI$ | STRING |
| | | | |
| TO | none | TO | |
| | | | |
| USR | U <SHIFT+S> | | NUMERIC |
| | | | |
| VAL | V <SHIFT+A> | | NUMERIC |
| | | | |
| VERIFY | V <SHIFT+E> | | |
| | | | |
| WAIT | W <SHIFT+A> | | |
+-----------+----------------------+----------------+-------------------+
34 BASIC LANGUAGE VOCABULARY
~
DESCRIPTION OF BASIC KEYWORDS
ABS
TYPE: Function-Numeric
FORMAT: ABS(<expression>)
Action: Returns the absolute value of the number, which is its value
without any signs. The absolute value of a negative number is that
number multiplied by -1.
EXAMPLES of ABS Function:
10 X = ABS (Y)
10 PRINT ABS (X*J)
10 IF X = ABS (X) THEN PRINT"POSITIVE"
AND
TYPE: Operator
FORMAT: <expression> AND <expression>
Action: AND is used in Boolean operations to test bits. it is also used
in operations to check the truth of both operands.
In Boolean algebra, the result of an AND operation is 1 only if both
numbers being ANDed are 1. The result is 0 if either or both is 0
(false).
EXAMPLES of 1-Bit AND operation:
0 1 0 1
AND 0 AND 0 AND 1 AND 1
------ ----- ----- -----
0 0 0 1
The Commodore 64 performs the AND operation on numbers in the range
from -32768 to +32767. Any fractional values are not used, and numbers
beyond the range will cause an ?ILLEGAL QUANTITY error message. When
BASIC LANGUAGE VOCABULARY 35
~
converted to binary format, the range allowed yields 16 bits for each
number. Corresponding bits are ANDed together, forming a 16-bit result
in the same range.
EXAMPLES of 16-Bit AND Operation:
17
AND 194
--------
0000000000010001
AND 0000000011000010
--------------------------
(BINARY) 0000000000000000
--------------------------
(DECIMAL) 0
32007
AND 28761
----------
0111110100000111
AND 0111000001011001
--------------------------
(BINARY) 0111000000000001
--------------------------
(DECIMAL) 28673
-241
AND 15359
----------
1111111100001111
AND 0011101111111111
--------------------------
(BINARY) 0011101100001111
--------------------------
(DECIMAL) 15119
36 BASIC LANGUAGE VOCABULARY
~
When evaluating a number for truth or falsehood, the computer assumes
the number is true as long as its value isn't 0. When evaluating a
comparison, it assigns a value of -I if the result is true, while false
has a value of 0. In binary format, -1 is all 1's and 0 is all 0's.
Therefore, when ANDing true/false evaluations, the result will be true if
any bits in the result are true.
EXAMPLES of Using AND with True/False Evaluations:
50 IF X=7 AND W=3 THEN GOTO 10: REM ONLY TRUE IF BOTH X=7
AND W=3 ARE TRUE
60 IF A AND Q=7 THEN GOTO 10: REM TRUE IF A IS NON-ZERO
AND Q=7 IS TRUE
ASC
TYPE: Function-Numeric
FORMAT: ASC(<string>)
Action: ASC will return a number from 0 to 255 which corresponds to
the Commodore ASCII value of the first character in the string. The table
of Commodore ASCII values is shown in Appendix C.
EXAMPLES OF ASC Function:
10 PRINT ASC("Z")
20 X = ASC("ZEBRA")
30 J = ASC(J$)
If there are no characters in the string, an ?ILLEGAL QUANTITY error
results. In the third example above, if J$="", the ASC function will not
work. The GET and GET# statement read a CHR$(0) as a null string. To
eliminate this problem, you should add a CHR$(0) to the end of the
string as shown below.
EXAMPLE of ASC Function Avoiding ILLEGAL QUANTITY ERROR:
30 J = ASC(J$ + CHR$(0))
BASIC LANGUAGE VOCABULARY 37
~
ATN
TYPE: Function-Numeric
FORMAT: ATN(<number>)
Action: This mathematical function returns the arctangent of the
number. The result is the angle (in radians) whose tangent is the number
given. The result is always in the range -pi/2 to +pi/2.
EXAMPLES of ATN Function:
10 PRINT ATN(0)
20 X = ATN(J)*180/ {pi} : REM CONVERT TO DEGREES
CHR$
TYPE: Function-String
FORMAT: CHR$ (<number>)
Action: This function converts a Commodore ASCII code to its character
equivalent. See Appendix C for a list of characters and their codes. The
number must have a value between 0 and 255, or an ?ILLEGAL QUANTITY error
message results.
EXAMPLES of CHR$ Function:
10 PRINT CHR$(65) : REM 65 = UPPER CASE A
20 A$=CHR$(13) : REM 13 = RETURN KEY
50 A=ASC(A$) : A$ = CHR$(A) : REM CONVERTS TO C64 ASCII CODE AND BACK
38 BASIC LANGUAGE VOCABULARY
~
CLOSE
TYPE: I/O Statement
FORMAT: CLOSE <file number>
Action: This statement shuts off any data file or channel to a device.
The file number is the same as when the file or device was OPENed (see
OPEN statement and the section on INPUT/OUTPUT programming).
When working with storage devices like cassette tape and disks, the
CLOSE operation stores any incomplete buffers to the device. When this
is not performed, the file will be incomplete on the tape and unreadable
on the disk. The CLOSE operation isn't as necessary with other devices,
but it does free up memory for other files. See your external device
manual for more details.
EXAMPLES of CLOSE Statement:
10 CLOSE 1
20 CLOSE X
30 CLOSE 9*(1+J)
CLR
TYPE: Statement
FORMAT: CLR
Action: This statement makes available RAM memory that had been used
but is no longer needed. Any BASIC program in memory is untouched, but
all variables, arrays, GOSUB addresses, FOR...NEXT loops, user-defined
functions, and files are erased from memory, and their space is mode
available to new variables, etc.
BASIC LANGUAGE VOCABULARY 39
~
In the case of files to the disk and cassette tape, they are not
properly CLOSED by the CLR statement. The information about the files is
lost to the computer, including any incomplete buffers. The disk drive
will still think the file is OPEN. See the CLOSE statement for more
information on this.
EXAMPLE of CLR Statement:
10 X=25
20 CLR
30 PRINT X
RUN
0
READY
CMD
TYPE: I/O Statement
FORMAT: <file number> [,string]
Action: This statement switches the primary- output device from the TV
screen to the file specified. This file could be on disk, tape, printer,
or an I/O device like the modem. The file number must be specified in a
prior OPEN statement. The string, when specified, is sent to the file.
This is handy for titling printouts, etc.
When this command is in effect, any PRINT statements and LIST commands
will not display on the screen, but will send the text in the same
format to the file.
To re-direct the output back to the screen, the PRINT# command should
send a blank line to the CMD device before CLOSEing, so it will
stop expecting data (called "un-listening" the device).
40 BASIC LANGUAGE VOCABULARY
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Any system error (like ?SYNTAX ERROR) will cause output to return to
the screen. Devices aren't un-listened by this, so you should send a
blank line after an error condition. (See your printer or disk manual for
more details.)
EXAMPLES of CMD Statement:
OPEN 4,4: CMD 4,"TITLE" : LIST: REM LISTS PROGRAM ON PRINTER
PRINT#4: CLOSE 4: REM UN-LISTENS AND CLOSES PRINTER
10 OPEN 1,1,1,"TEST" : REM CREATE SEQ FILE
20 CMD 1 : REM OUTPUT TO TAPE FILE, NOT SCREEN
30 FOR L = 1 TO 100
40 PRINT L: REM PUTS NUMBER IN TAPE BUFFER
50 NEXT
60 PRINT#1 : REM UNLISTEN
70 CLOSE 1 : REM WRITE UNFINISHED BUFFER, PROPERLY FINISH
CONT
TYPE: Command
FORMAT: CONT
Action: This command re-starts the execution of a program which was
halted by a STOP or END statement or the <RUN/STOP> key being pressed.
The program will re-start at the exact place from which it left off.
While the program is stopped, the user can inspect or change any
variables or look at the program. When debugging or examining a program,
STOP statements can be placed at strategic locations to allow examination
of variables and to check the flow of the program.
The error message CAN'T CONTINUE will result from editing the program
(even just hitting <RETURN> with the cursor on an unchanged line), or if
the program halted due to an error, or if you caused an error before
typing CONT to re-start the program.
EXAMPLE of CONT Command:
10 PI=0:C=1
20 PI=PI+4/C-4/(C+2)
30 PRINT PI
40 C=C+4:GOTO 20
BASIC LANGUAGE VOCABULARY 41
~
This program calculates the value of PI. RUN this program, and after
a short while hit the <RUN/STOP> key. You will see the display:
+----------------------------------+
BREAK IN 20 | NOTE: Might be different number. |
+----------------------------------+
Type the command PRINT C to see how far the Commodore 64 has gotten.
Then use CONT to resume from where the Commodore 64 left off.
COS
TYPE: Function
FORMAT: COS (<number>)
Action: This mathematical function calculates the cosine of the number,
where the number is an angle in radians.
EXAMPLES of COS Function:
10 PRINT COS(0)
20 X = COS(Y* {pi} /180) : REM CONVERT DEGREES TO RADIANS
DATA
TYPE: Statement
FORMAT: DATA <list of constants>
Action: DATA statements store information within a program. The program
uses the information by means of the READ statement, which pulls
successive constants from the DATA statements.
The DATA statements don't have to be executed by the program, they
only have to be present. Therefore, they are usually placed at the end of
the program.
All data statements in a program are treated as a continuous list. Data
is READ from left to right, from the lowest numbered line to the highest.
If the READ statement encounters data that doesn't fit the type requested
(if it needs a number and finds a string) an error message occurs.
42 BASIC LANGUAGE VOCABULARY
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Any characters can be included as data, but if certain ones are used
the data item must be enclosed by quote marks (" "). These include
punctuation like comma (,), colon (:), blank spaces, and shifted letters,
graphics, and cursor control characters.
EXAMPLES of DATA Statement:
10 DATA 1,10,5,8
20 DATA JOHN,PAUL,GEORGE,RINGO
30 DATA "DEAR MARY, HOW ARE YOU, LOVE, BILL"
40 DATA -1.7E-9, 3.33
DEF FN
TYPE: Statement
FORMAT: DEF FN <name> ( <variable> ) = <expression>
Action: This sets up a user-defined function that can be used later in
the program. The function can consist of any mathematical formula. User-
defined functions save space in programs where a long formula is used in
several places. The formula need only be specified once, in the
definition statement, and then it is abbreviated as a function name. It
must be executed once, but any subsequent executions are ignored.
The function name is the letters FN followed by any variable name. This
can be 1 or 2 characters, the first being a letter and the second a
letter or digit.
EXAMPLES of DEF FN Statement:
10 DEF FN A(X)=X+7
20 DEF FN AA(X)=Y*Z
30 DEF FN A9(Q) = INT(RND(1)*Q+1)
The function is called later in the program by using the function name
with a variable in parentheses. This function name is used like any other
variable, and its value is automatically calculated,
BASIC LANGUAGE VOCABULARY 43
~
EXAMPLES of FN Use:
40 PRINT FN A(9)
50 R=FN AA(9)
60 G=G+FN A9(10)
In line 50 above, the number 9 inside the parentheses does not affect
the outcome of the function, because the function definition in line 20
doesn't use the variable in the parentheses. The result is Y times Z,
regardless of the value of X. In the other two functions, the value in
parentheses does affect the result.
DIM
TYPE: Statement
FORMAT: DIM <variable> ( <subscripts> )[
<variable> ( <subscripts> )...]
Action: This statement defines an array or matrix of variables. This
allows you to use the variable name with a subscript. The subscript
points to the element being used. The lowest element number in an array
is zero, and the highest is the number given in the DIM statement, which
has a maximum of 32767.
The DIM statement must be executed once and only once for each array.
A REDIM'D ARRAY error occurs if this line is re-executed. Therefore,
most programs perform all DIM operations at the very beginning.
There may be any number of dimensions and 255 subscripts in an array,
limited only by the amount of RAM memory which is available to hold the
variables. The array may be mode up of normal numeric variables, as shown
above, or of strings or integer numbers. If the variables are other than
normal numeric, use the $ or % signs after the variable name to indicate
string or integer variables,
44 BASIC LANGUAGE VOCABULARY
~
If an array referenced in a program was never DiMensioned, it is
automatically dimensioned to 11 elements in each dimension used in the
first reference.
EXAMPLES of DIM Statement:
10 DIM A(100)
20 DIM Z (5,7), Y(3,4,5)
30 DIM Y7%(Q)
40 DIM PH$(1000)
50 F(4)=9 : REM AUTOMATICALLY PERFORMS DIM F(10)
EXAMPLE of FOOTBALL SCORE-KEEPING Using DIM:
10 DIM S(1,5), T$(1)
20 INPUT"TEAM NAMES"; T$(0), T$(1)
30 FOR Q=1 TO 5: FOR T=0 TO 1
40 PRINT T$(T),"SCORE IN QUARTER" Q
50 INPUT S(T,Q): S(T,0)= S(T,0)+ S(T,Q)
60 NEXT T,Q
70 PRINT CHR$(147) "SCOREBOARD"
80 PRINT "QUARTER"
90 FOR Q= 1 TO 5
100 PRINT TAB(Q*2+9) Q;
110 NEXT: PRINT TAB(15) "TOTAL"
120 FOR T=0 TO 1: PRINT T$(T);
130 FOR Q= 1 TO 5
140 PRINT TAB(Q*2+9) S(T,Q);
150 NEXT: PRINT TAB(15) S(T,0)
160 NEXT
CALCULATING MEMORY USED BY DIM:
5 bytes for the array name
2 bytes for each dimension
2 bytes/element for integer variables
5 bytes/element for normal numeric variables
3 bytes/element for string variables
1 byte for each character in each string element
BASIC LANGUAGE VOCABULARY 45
~
END
TYPE: Statement
FORMAT: END
Action: This finishes a program's execution and displays the READY
message, returning control to the person operating the computer. There
may be any number of END statements within a program. While it is not
necessary to include any END statements at all, it is recommended that
a program does conclude with one, rather than just running out of lines.
The END statement is similar to the STOP statement. The only difference
is that STOP causes the computer to display the message BREAK IN LINE XX
and END just displays READY. Both statements allow the computer to resume
execution by typing the CONT command.
EXAMPLES of END Statement:
10 PRINT"DO YOU REALLY WANT TO RUN THIS PROGRAM"
20 INPUT A$
30 IF A$ = "NO" THEN END
40 REM REST OF PROGRAM . . .
999 END
EXP
TYPE: Function-Numeric
FORMAT: EXP ( <number> )
Action: This mathematical function calculates the constant e
(2.71828183) raised to the power of the number given. A value greater
than 88.0296919 causes an ?OVERFLOW error to occur.
EXAMPLES of EXP Function:
10 PRINT EXP (1)
20 X = Y*EXP (Z*Q)
46 BASIC LANGUAGE VOCABULARY
~
FN
TYPE: Function-Numeric
FORMAT: FN <name> ( <number> )
Action: This function references the previously DEFined formula spec-
ified by name. The number is substituted into its place (if any) and the
formula is calculated. The result will be a numeric value.
This function can be used in direct mode, as long as the statement
DEFining it has been executed.
If an FN is executed before the DEF statement which defines it, an
UNDEF'D FUNCTION error occurs.
EXAMPLES of FN (User-Defined) Function:
PRINT FN A(Q)
1100 J = FN J(7)+ FN J(9)
9990 IF FN B7 (1+1)= 6 THEN END
FOR ... TO ... [STEP ...
TYPE: Statement
FORMAT: FOR <variable> = <start> TO <limit> [ STEP <increment> ]
Action: This is a special BASIC statement that lets you easily use a
variable as a counter. You must specify certain parameters: the
floating-point variable name, its starting value, the limit of the count,
and how much to add during each cycle.
Here is a simple BASIC program that counts from 1 to 10, PRINTing
each number and ENDing when complete, and using no FOR statements:
100 L = 1
110 PRINT L
120 L = 1 + 1
130 IF L <= 10 THEN 110
140 END
BASIC LANGUAGE VOCABULARY 47
~
Using the FOR statement, here is the same program:
100 FOR L = 1 TO 10
110 PRINT L
120 NEXT L
130 END
As you can see, the program is shorter and easier to understand using
the FOR statement.
When the FOR statement is executed, several operations take place.
The <start> value is placed in the <variable> being used in the
counter. In the example above, a I is placed in L.
When the NEXT statement is reached, the <increment> value is added to
the <variable>. If a STEP was not included, the <increment> is set to
+ 1. The first time the program above hits line 120, 1 is added to L,
so the new value of L is 2.
Now the value in the <variable> is compared to the <limit>. If the
<limit> has not been reached yet, the program G0es TO the line after
the original FOR statement. In this case, the value of 2 in L is less
than the limit of 10, so it GOes TO line 110.
Eventually, the value of <limit> is exceeded by the <variable>. At
that time, the loop is concluded and the program continues with the line
following the NEXT statement. In our example, the value of L reaches
11, which exceeds the limit of 10, and the program goes on with line
130.
When the value of <increment> is positive, the <variable> must
exceed the <limit>, and when it is negative it must become less than
the <limit>.
+---------------------------------------------+
| NOTE: A loop always executes at least once. |
+---------------------------------------------+
EXAMPLES of FOR...TO...STEP...Statement:
100 FOR L = 100 TO 0 STEP -1
100 FOR L = PI TO 6* {pi} STEP .01
100 FOR AA = 3 TO 3
48 BASIC LANGUAGE VOCABULARY
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FRE
TYPE: Function
FORMAT: FRE ( <variable> )
Action: This function tells you how much RAM is available for your
program and its variables. If a program tries to use more space than is
available, the OUT OF MEMORY error results.
The number in parentheses can have any value, and it is not used in
the calculation.
+-----------------------------------------------------------------------+
| NOTE: If the result of FRE is negative, add 65536 to the FRE number |
| get the number of bytes available in memory. |
+-----------------------------------------------------------------------+
EXAMPLES of FRE Function:
PRINT FRE(0)
10 X = (FRE(K)-1000)/7
950 IF FRE(0)< 100 THEN PRINT "NOT ENOUGH ROOM"
+-----------------------------------------------------------------------+
| NOTE: The following always tells you the current available RAM: |
| PRINT FRE(0) - (FRE(0) < 0)* 65536 |
+-----------------------------------------------------------------------+
GET
TYPE: Statement
FORMAT: GET <variable list>
Action: This statement reads each key typed by the user. As the user is
typing, the characters are stored in the Commodore 64's keyboard buffer.
Up to 10 characters are stored here, and any keys struck after the 10th
are lost. Reading one of the characters with the GET statement makes room
for another character.
If the GET statement specifies numeric data, and the user types a key
other than a number, the message ?SYNTAX ERROR appears. To be safe, read
the keys as strings and convert them to numbers later.
BASIC LANGUAGE VOCABULARY 49
~
The GET statement can be used to avoid some of the limitations of the
INPUT statement. For more on this, see the section on Using the GET
Statement in the Programming Techniques section.
EXAMPLES of GET Statement:
10 GET A$: IF A$ ="" THEN 10: REM LOOPS IN 10 UNTIL ANY KEY HIT
20 GET A$, B$, C$, D$, E$: REM READS 5 KEYS
30 GET A, A$
GET#
TYPE: I/O Statement
FORMAT: GET# <file number>, <variable list>
Action: This statement reads characters one-at-a-time from the device
or file specified. It works the same as the GET statement, except that
the data comes from a different place than the keyboard. If no character
is received, the variable is set to an empty string (equal to "") or to 0
for numeric variables. Characters used to separate data in files, like
the comma (,) or <RETURN> key code (ASC code of 13), are received like
any other character.
When used with device #3 (TV screen), this statement will read char-
acters one by one from the screen. Each use of GET# moves the cursor 1
position to the right. The character at the end of the logical line is
changed to a CHR$ (13), the <RETURN> key code.
EXAMPLES of GET# Statement:
5 GET#1, A$
10 OPEN 1,3: GET#1, Z7$
20 GET#1, A, B, C$, D$
50 BASIC LANGUAGE VOCABULARY
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GOSUB
TYPE: Statement
FORMAT: GOSUB <line number>
Action: This is a specialized form of the GOTO statement, with one
important difference: GOSUB remembers where it came from. When the
RETURN statement (different from the <RETURN> key on the keyboard)
is reached in the program, the program jumps back to the statement
immediately following the original GOSUB statement.
The major use of a subroutine (GOSUB really means GO to a SUBroutine)
is when a small section of program is used by different sections of the
program. By using subroutines rather than repeating the same lines over
and over at different places in the program, you can save lots of program
space. In this way, GOSUB is similar to DEF FN. DEF FN lets you save
space when using a formula, while GOSUB saves space when using a several-
line routine. Here is an inefficient program that doesn't use GOSUB:
100 PRINT "THIS PROGRAM PRINTS"
110 FOR L = 1 TO 500:NEXT
120 PRINT "SLOWLY ON THE SCREEN"
130 FOR L = 1 TO 500:NEXT
140 PRINT "USING A SIMPLE LOOP"
150 FOR L = 1 TO 500:NEXT
160 PRINT "AS A TIME DELAY."
170 FOR L = 1 TO 500:NEXT
Here is the same program using GOSUB:
100 PRINT "THIS PROGRAM PRINTS"
110 GOSUB 200
120 PRINT "SLOWLY ON THE SCREEN"
130 GOSUB 200
140 PRINT "USING A SIMPLE LOOP"
150 GOSUB 200
160 PRINT "AS A TIME DELAY."
170 GOSUB 200
180 END
200 FOR L = 1 TO 500 NEXT
210 RETURN
BASIC LANGUAGE VOCABULARY 51
~
Each time the program executes a GOSUB, the line number and position
in the program line are saved in a special area called the "stack,"
which takes up 256 bytes of your memory. This limits the amount of data
that can be stored in the stack. Therefore, the number of subroutine
return addresses that can be stored is limited, and care should be taken
to make sure every GOSUB hits the corresponding RETURN, or else you'll
run out of memory even though you have plenty of bytes free.
GOTO
TYPE: Statement
FORMAT :GOTO <line number>
or GO TO <line number>
Action: This statement allows the BASIC program to execute lines out
of numerical order. The word GOTO followed by a number will make the
program jump to the line with that number. GOTO NOT followed by a number
equals GOTO 0. It must have the line number after the word GOTO.
It is possible to create loops with GOTO that will never end. The
simplest example of this is a line that GOes TO itself, like 10 GOTO 10.
These loops can be stopped using the <RUN/STOP> key on the keyboard.
EXAMPLES of GOTO Statement:
GOTO 100
10 GO TO 50
20 GOTO 999
IF...THEN...
TYPE: Statement
FORMAT: IF <expression> THEN <line number>
IF <expression> GOTO <line number>
IF <expression> THEN <statements>
Action: This is the statement that gives BASIC most of its "intelli-
gence," the ability to evaluate conditions and take different actions de-
pending on the outcome.
52 BASIC LANGUAGE VOCABULARY
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The word IF is followed by an expression, which can include variables,
strings, numbers, comparisons, and logical operators. The word THEN
appears on the same line and is followed by either a line number or one
or more BASIC statements. When the expression is false, everything after
the word THEN on that line is ignored, and execution continues with the
next line number in the program. A true result makes the program either
branch to the line number after the word THEN or execute whatever other
BASIC statements are found on that line.
EXAMPLE of IF...GOTO...Statement:
100 INPUT "TYPE A NUMBER"; N
110 IF N <= 0 GOTO 200
120 PRINT "SQUARE ROOT=" SQR(N)
130 GOTO 100
200 PRINT "NUMBER MUST BE >0"
210 GOTO 100
This program prints out the square root of any positive number. The IF
statement here is used to validate the result of the INPUT. When the
result of N <= 0 is true, the program skips to line 200, and when the
result is false the next line to be executed is 120. Note that THEN GOTO
is not needed with IF...THEN, as in line 110 where GOTO 200 actually
means THEN GOTO 200.
EXAMPLE OF IF...THEN...Statement:
100 FOR L = 1 TO 100
110 IF RND(1) < .5 THEN X=X+1: GOTO 130
120 Y=Y+1
130 NEXT L
140 PRINT "HEADS=" X
150 PRINT "TAILS= " Y
The IF in line 110 tests a random number to see if it is less than .5.
When the result is true, the whole series of statements following the
word THEN are executed: first X is incremented by 1, then the program
skips to line 130. When the result is false, the program drops to the
next statement, line 120.
BASIC LANGUAGE VOCABULARY 53
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INPUT
TYPE: Statement
FORMAT: INPUT [ "<prompt>" ; ] <variable list>
Action: This is a statement that lets the person RUNning the program
"feed" information into the computer. When executed, this statement
PRINTs a question mark (?) on the screen, and positions the cursor 1
space to the right of the question mark. Now the computer waits, cursor
blinking, for the operator to type in the answer and press the <RETURN>
key.
The word INPUT may be followed by any text contained in quote marks
(""). This text is PRINTed on the screen, followed by the question mark.
After the text comes a semicolon (;) and the name of one or more
variables separated by commas. This variable is where the computer
stores the information that the operator types. The variable can be any
legal variable name, and you can have several different variable
names, each for a different input.
EXAMPLES of INPUT Statement:
100 INPUT A
110 INPUT B, C, D
120 INPUT "PROMPT"; E
When this program RUNs, the question mark appears to prompt the
operator that the Commodore 64 is expecting an input for line 100. Any
number typed in goes into A, for later use in the program. If the answer
typed was not a number, the ?REDO FROM START message appears, which means
that a string was received when a number was expected.
If the operator just hits <RETURN> without typing anything, the vari-
able's value doesn't change.
Now the next question mark, for line 110, appears. If we type only
one number and hit the <RETURN>, Commodore 64 will now display 2
question marks (??), which means that more input is required. You can
54 BASIC LANGUAGE VOCABULARY
~
just type as many inputs as you need separated by commas, which prevents
the double question mark from appearing. If you type more data than the
INPUT statement requested, the ?EXTRA IGNORED message appears, which
means that the extra items you typed were not put into any variables.
Line 120 displays the word PROMPT before the question mark appears. The
semicolon is required between the prompt and any list of variables.
The INPUT statement can never be used outside a program. The Commodore
64 needs space for a buffer for the INPUT variables, the same space that
is used for commands.
INPUT#
TYPE: I/O Statement
FORMAT: INPUT# <file number> , <variable list>
Action: This is usually the fastest and easiest way to retrieve data
stored in a file on disk or tape. The data is in the form of whole vari-
ables of up to 80 characters in length, as opposed to the one-at-a-time
method of GET#. First, the file must have been OPENed, then INPUT# can
fill the variables.
The INPUT# command assumes a variable is finished when it reads a
RETURN code (CHR$ (13)), a comma (,), semicolon (;), or colon (:).
Quote marks can be used to enclose these characters when writing if
they are needed (see PRINT# statement).
If the variable type used is numeric, and non-numeric characters are
received, a BAD DATA error results. INPUT# can read strings up to 80
characters long, beyond which a STRING TOO LONG error results.
When used with device #3 (the screen), this statement will read an
entire logical line and move the cursor down to the next line.
EXAMPLES of INPUT# Statement:
10 INPUT#1,A
20 INPUT#2,A$,B$
BASIC LANGUAGE VOCABULARY 55
~
INT
TYPE: Integer Function
FORMAT: INT (<numeric>)
Action: Returns the integer value of the expression. If the expression
is positive, the fractional part is left off. If the expression is
negative, any fraction causes the next lower integer to be returned.
EXAMPLES of INT Function:
120 PRINT INT(99.4343), INT(-12.34)
99 -13
LEFT$
TYPE: String Function
FORMAT: LEFT$ (<string>, <integer>)
Action: Returns a string comprised of the leftmost <integer> char-
acters of the <string>. The integer argument value must be in the range
0 to 255. If the integer is greater than the length of the string, the
entire string will be returned. If an <integer> value of zero is used,
then a null string (of zero length) is returned.
EXAMPLES of LEFT$ Function:
10 A$ = "COMMODORE COMPUTERS"
20 B$ = LEFT$(A$,9): PRINT B$
RUN
COMMODORE
56 BASIC LANGUAGE VOCABULARY
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LEN
TYPE: Integer Function
Format: LEN (<string>)
Action: Returns the number of characters in the string expression.
Non-printed characters and blanks are counted.
EXAMPLE of LEN Function:
CC$ = "COMMODORE COMPUTER": PRINT LEN(CC$)
18
LET
TYPE: Statement
FORMAT: [LET] <variable> = <expression>
Action: The LET statement can be used to assign a value to a variable.
But the word LET is optional and therefore most advanced programmers
leave LET out because it's always understood and wastes valuable memory.
The equal sign (=) alone is sufficient when assigning the value of an
expression to a variable name.
EXAMPLES of LET Statement:
10 LET D= 12 (This is the same as D = 12)
20 LET E$ = "ABC"
30 F$ = "WORDS"
40 SUM$= E$ + F$ (SUM$ would equal ABCWORDS)
BASIC LANGUAGE VOCABULARY 57
~
LIST
TYPE: Command
FORMAT: LIST [[<first-line>]-[<last-line>]]
Action: The LIST command allows you to look at lines of the BASIC
program currently in the memory of your Commodore 64. This lets you use
your computer's powerful screen editor, to edit programs which you've
LISTed both quickly and easily.
The LIST system command displays all or part of the program that is
currently in memory on the default output device. The LIST will normally
be directed to the screen and the CMD statement can be used to switch
output to an external device such as a printer or a disk. The LIST com-
mand can appear in a program, but BASIC always returns to the system
READY message after a LIST is executed.
When you bring the program LIST onto the screen, the "scrolling" of
the display from the bottom of the screen to the top can be slowed by
holding down the ConTRoL <CTRL> key. LIST is aborted by typing the
<RUN/STOP> key.
If no line-numbers are given the entire program is listed. If only the
first-line number is specified, and followed by a hyphen (-), that line
and all higher-numbered lines are listed. If only the last line-number is
specified, and it is preceded by a hyphen, then all lines from the
beginning of the program through that line are listed. If both numbers
are specified, the entire range, including the line-numbers LISTed, is
displayed.
EXAMPLES of LIST Command:
LIST (Lists the program currently in memory.)
LIST 500 (Lists line 500 only.)
LIST 150- (Lists all lines from 150 to the end.)
LIST -1000 (Lists all lines from the lowest through 1000.)
LIST 150-1000 (Lists lines 150 through 1000, inclusive.)
10 PRINT "THIS IS LINE 10"
20 LIST (LIST used in Program Mode)
30 PRINT "THIS IS LINE 30"
58 BASIC LANGUAGE VOCABULARY
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LOAD
TYPE: Command
FORMAT: LOAD["<file-name>"][,<device>][,<address>]
Action: The LOAD statement reads the contents of a program file from
tape or disk into memory. That way you can use the information LOADed
or change the information in some way. The device number is optional,
but when it is left out the computer will automatically default to 1, the
cassette unit. The disk unit is normally device number 8. The LOAD closes
all open files and, if it is used in direct mode, it performs a CLR
(clear) before reading the program. If LOAD is executed from within a
program, the program is RUN. This means that you can use LOAD to "chain"
several programs together. None of the variables are cleared during a
chain operation.
If you are using file-name pattern matching, the first file which
matches the pattern is loaded. The asterisk in quotes by itself ("*")
causes the first file-name in the disk directory to be loaded. if the
filename used does not exist or if it is not a program file, the BASIC
error message ?FILE NOT FOUND occurs.
When LOADing programs from tape, the <file-name> can be left out, and
the next program file on the tape will be read. The Commodore 64 will
blank the screen to the border color after the PLAY key is pressed. When
the program is found, the screen clears to the background color and the
"FOUND" message is displayed. When the <C=> key, <CTRL> key, <ARROW LEFT>
key, or <SPACE BAR> is pressed, the file will be loaded. Programs will
LOAD starting at memory location 2048 unless a secondary <address> of 1
is used. If you use the secondary address of 1 this will cause the
program to LOAD to the memory location from which it was saved.
BASIC LANGUAGE VOCABULARY 59
~
EXAMPLES of LOAD Command:
LOAD (Reads the next program on tape)
LOAD A$ (Uses the name in A$ to search)
LOAD"*",8 (LOADs first program from disk)
LOAD"",1,1 (Looks for the first program on
tape, and LOADs it into the same
part of memory that it came from)
LOAD"STAR TREK" (LOAD a file from tape)
PRESS PLAY ON TAPE
FOUND STAR TREK
LOADING
READY.
LOAD"FUN",8 (LOAD a file from disk)
SEARCHING FOR FUN
LOADING
READY.
LOAD"GAME ONE",8,1 (LOAD a file to the specific
SEARCHING FOR GAME ONE memory location from which the
LOADING program was saved on the disk)
READY.
60 BASIC LANGUAGE VOCABULARY
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LOG
TYPE: Floating-Point Function
FORMAT: LOG(<numeric>)
Action: Returns the natural logarithm (log to the base of e) of the
argument. If the value of the argument is zero or negative the BASIC
error message ?ILLEGAL QUANTITY will occur.
EXAMPLES of LOG Function:
25 PRINT LOG(45/7)
1.86075234
10 NUM=LOG(ARG)/LOG(10) (Calculates the LOG of ARG to the base 10)
MID$
TYPE: String Function
FORMAT: MID$(<string>,<numeric-1>[,<numeric-2>])
Action: The MID$ function returns a sub-string which is taken from
within a larger <string> argument. The starting position of the sub-
string is defined by the <numeric-1> argument and the length of the
sub-string by the <numeric-2> argument. Both of the numeric arguments
can have values ranging from 0 to 255.
If the <numeric-1> value is greater than the length of the <string>,
or if the <numeric-2> value is zero, then MID$ gives a null string value.
If the <numeric-2> argument is left out, then the computer will assume
that a length of the rest of the string is to be used. And if the source
string has fewer characters than <numeric-2>, from the starting position
to the end of the string argument, then the whole rest of the string is
used.
EXAMPLE of MID$ Function:
10 A$="GOOD"
20 B$="MORNING EVENING AFTERNOON"
30 PRINT A$ + MID$(B$,8,8)
GOOD EVENING
BASIC LANGUAGE VOCABULARY 61
~
NEW
TYPE: Command
FORMAT: NEW
Action: The NEW command is used to delete the program currently in
memory and clear all variables. Before typing in a new program, NEW
should be used in direct mode to clear memory. NEW can also be used in
a program, but you should be aware of the fact that it will erase
everything that has gone before and is still in the computer's memory.
This can be particularly troublesome when you're trying to debug your
program.
+-----------------------------------------------------------------------+
| BE CAREFUL: Not clearing out an old program before typing a new one |
| can result in a confusing mix of the two programs. |
+-----------------------------------------------------------------------+
EXAMPLES of NEW Command:
NEW (Clears the program and all variables)
10 NEW (Performs a NEW operation and STOPs the program.)
NEXT
TYPE: Statement
FORMAT: NEXT[<counter>][,<counter>]...
Action: The NEXT statement is used with FOR to establish the end of a
FOR...NEXT loop. The NEXT need not be physically the last statement
in the loop, but it is always the last statement executed in a loop. The
<counter> is the loop index's variable name used with FOR to start the
loop. A single NEXT can stop several nested loops when it is followed by
each FOR's <counter> variable name(s). To do this each name must appear
in the order of inner-most nested loop first, to outer-most nested loop
last. When using a single NEXT to increment and stop several variable
names, each variable name must be separated by commas. Loops can be
nested to 9 levels. If the counter variable(s) are omitted, the counter
associated with the FOR of the current level (of the nested loops) is
incremented.
62 BASIC LANGUAGE VOCABULARY
~
When the NEXT is reached, the counter value is incremented by 1 or by
an optional STEP value. It is then tested against an end-value to see if
it's time to stop the loop. A loop will be stopped when a NEXT is found
which has its counter value greater than the end-value.
EXAMPLES of NEXT Statement:
10 FOR J=1 TO 5: FOR K=10 TO 20: FOR N=5 TO -5 STEP - 1
20 NEXT N,K,J (Stopping Nested Loops)
10 FOR L=1 TO 100
20 FOR M=1 TO 10
30 NEXT M
400 NEXT L (Note how the loops do NOT cross each other)
10 FOR A=1 TO 10
20 FOR B=1 TO 20
30 NEXT
40 NEXT (Notice that no variable names are needed)
NOT
TYPE: Logical Operator
FORMAT: NOT <expression>
Action: The NOT logical operator "complements" the value of each bit
in its single operand, producing an integer "twos-complement" result. In
other words, the NOT is really saying, "if it isn't. When working with a
floating-point number, the operands are converted to integers and any
fractions are lost. The NOT operator can also be used in a comparison to
reverse the true/false value which was the result of a relationship test
and therefore it will reverse the meaning of the comparison. In the first
example below, if the "twos-complement" of "AA" is equal to "BB" and if
"BB" is NOT equal to "CC" then the expression is true.
BASIC LANGUAGE VOCABULARY 63
~
EXAMPLES of NOT Operator:
10 IF NOT AA = BB AND NOT(BB = CC) THEN...
NN% = NOT 96: PRINT NN%
-97
+-----------------------------------------------------------------------+
| NOTE: TO find the value of NOT use the expression X=(-(X+1)). (The |
| two's complement of any integer is the bit complement plus one.) |
+-----------------------------------------------------------------------+
ON
TYPE: Statement
FORMAT: ON <variable> GOTO / GOSUB <line-number>[,<line-number>]...
Action: The ON statement is used to GOTO one of several given line-
numbers, depending upon the value of a variable. The value of the
variables can range from zero through the number of lines given. if the
value is a non-integer, the fractional portion is left off. For example,
if the variable value is 3, ON will GOTO the third line-number in the
list.
If the value of the variable is negative, the BASIC error message
?ILLEGAL QUANTITY occurs. If the number is zero, or greater than the
number of items in the list, the program just "ignores" the statement and
continues with the statement following the ON statement.
ON is really an underused variant of the IF...THEN...statement. Instead
of using a whole lot of IF statements each of which sends the program to
1 specific line, 1 ON statement can replace a list of IF statements. When
you look at the first example you should notice that the 1 ON statement
replaces 4 IF...THEN... statements.
EXAMPLES of ON Statement:
ON -(A=7)-2*(A=3)-3*(A<3)-4*(A>7)GOTO 400,900,1000,100
ON X GOTO 100,130,180,220
ON X+3 GOSUB 9000,20,9000
100 ON NUM GOTO 150,300,320,390
500 ON SUM/2 + 1 GOSUB 50,80,20
64 BASIC LANGUAGE VOCABULARY
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OPEN
TYPE: I/O Statement
FORMAT: OPEN <file-num>,[<device>][,<address>]
[,"<File-name> [,<type>] [,<mode>]"]
Action: This statement OPENs a channel for input and/or output to a
peripheral device. However, you may NOT need all those parts for every
OPEN statement. Some OPEN statements require only 2 codes:
1) LOGICAL FILE NUMBER
2) DEVICE NUMBER
The <file-num> is the logical file number, which relates the OPEN,
CLOSE, CMD, GET#, INPUT#, and PRINT# statements to each other and
associates them with the file-name and the piece of equipment being used.
The logical file number can range from 1 to 255 and you can assign it any
number you want in that range.
+-----------------------------------------------------------------------+
| NOTE: File numbers over 128 were really designed for other uses so |
| it's good practice to use only numbers below 127 for file numbers. |
+-----------------------------------------------------------------------+
Each peripheral device (printer, disk drive, cassette) in the system
has its own number which it answers to. The <device> number is used with
OPEN to specify on which device the data file exists. Peripherals like
cassette decks, disk drives or printers also answer to several secondary
addresses. Think of these as codes which tell each device what operation
to perform. The device logical file number is used with every GET#,
INPUT#, and PRINT#.
If the <device> number is left out the computer will automatically
assume that you want your information to be sent to and received from
the Datassette(TM), which is device number 1. The file-name can also be
left out, but later on in your program, you can NOT call the file by name
if you have not already given it one. When you are storing files on cas-
sette tape, the computer will assume that the secondary <address> is
zero (0) if you omit the secondary address (a READ operation).
BASIC LANGUAGE VOCABULARY 65
~
A secondary address value of one (1) OPENs cassette tape files for
writing. A secondary address value of two (2) causes an end-of-tape
marker to be written when the file is later closed. The end-of-tape
marker prevents accidentally reading past the end of data which results
in the BASIC error message ?DEVICE NOT PRESENT.
For disk files, the secondary addresses 2 thru 14 are available for
data-files, but other numbers have special meanings in DOS commands.
You must use a secondary address when using your disk drive(s). (See
your disk drive manual for DOS command details.)
The <file-name> is a string of 1-16 characters and is optional for
cassette or printer files. If the file <type> is left out the type of
file will automatically default to the Program file unless the <mode> is
given.
Sequential files are OPENed for reading <mode>=R unless you specify that
files should be OPENed for writing <mode> =W is specified. A file <type>
can be used to OPEN an existing Relative file. Use REL for <type> with
Relative files. Relative and Sequential files are for disk only.
If you try to access a file before it is OPENed the BASIC error message
?FILE NOT OPEN will occur. If you try to OPEN a file for reading which
does not exist the BASIC error message ?FILE NOT FOUND will occur. If
a file is OPENed to disk for writing and the file-name already exists,
the DOS error message FILE EXISTS occurs. There is no check of this type
available for tape files, so be sure that the tape is properly positioned
or you might accidentally write over some data that had previously been
SAVED. If a file is OPENed that is already OPEN, the BASIC error message
FILE OPEN occurs. (See Printer Manual for further details.)
66 BASIC LANGUAGE VOCABULARY
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EXAMPLES of OPEN Statements:
10 OPEN 2,8,4,"DISK-OUTPUT,SEQ,W" (Opens sequential file on disk)
10 OPEN 1,1,2,"TAPE-WRITE" (Write End-of-File on Close)
10 OPEN 50,0 (Keyboard input)
10 OPEN 12,3 (Screen output)
10 OPEN 130,4 (Printer output)
10 OPEN 1,1,0,"NAME" (Read from cassette)
10 OPEN 1,1,1,"NAME" (Write to cassette)
10 OPEN 1,2,0,CHR$(10) (open channel to RS-232 device)
10 OPEN 1,4,0,"STRING" (Send upper case/graphics to
the printer)
10 OPEN 1,4,7,"STRING" (Send upper/lower case to
printer)
10 OPEN 1,5,7,"STRING" (Send upper/lower case to
printer with device # 5)
10 OPEN 1,8,15,"COMMAND" (Send a command to disk)
BASIC LANGUAGE VOCABULARY 67
~
OR
TYPE: Logical Operator
FORMAT: <operand> OR <operand>
Action: Just as the relational operators can be used to make decisions
regarding program flow, logical operators can connect two or more re-
lations and return a true or false value which can then be used in a
decision. When used in calculations, the logical OR gives you a bit
result of I if the corresponding bit of either or both operands is 1.
This will produce an integer as a result depending on the values of the
operands. When used in comparisons the logical OR operator is also used
to link two expressions into a single compound expression. If either of
the expressions are true, the combined expression value is true (-1). In
the first example below if AA is equal to BB OR if XX is 20, the
expression is true.
Logical operators work by converting their operands to 16-bit, signed,
two's complement integers in the range of -32768 to +32767. If the
operands are not in the range an error message results. Each bit of the
result is determined by the corresponding bits in the two operands.
EXAMPLES of OR Operator:
100 IF (AA=BB) OR (XX=20) THEN...
230 KK%=64 OR 32: PRINT KK% (You typed this with a bit
value of 1000000 for 64
and 100000 for 32)
96 (The computer responded with
bit value 1100000.
1100000=96.)
68 BASIC LANGUAGE VOCABULARY
~
PEEK
TYPE: Integer Function
FORMAT: PEEK(<numeric>)
Action: Returns an integer in the range of 0 to 255, which is read
from a memory location. The <numeric> expression is a memory location
which must be in the range of 0 to 65535. If it isn't then the BASIC
error message ?ILLEGAL QUANTITY occurs.
EXAMPLES of PEEK Function:
10 PRINT PEEK(53280) AND 15 (Returns value of screen border color)
5 A%=PEEK(45)+PEEK(46)*256 (Returns address of BASIC variable table)
POKE
TYPE: Statement
FORMAT: POKE <location>,<value>
Action: The POKE statement is used to write a one-byte (8-bits) binary
value into a given memory location or input/output register. The
<location> is an arithmetic expression which must equal a value in the
range of 0 to 65535. The <value> is an expression which can be reduced to
an integer value of 0 to 255. If either value is out of its respective
range, the BASIC error message ?ILLEGAL QUANTITY occurs.
The POKE statement and PEEK statement (which is a built-in function
that looks at a memory location) are useful for data storage, controlling
graphics displays or sound generation, loading assembly language sub-
routines, and passing arguments and results to and from assembly language
subroutines. In addition, Operating System parameters can be examined
using PEEK statements or changed and manipulated using POKE statements.
A complete memory map of useful locations is given in Appendix G.
BASIC LANGUAGE VOCABULARY 69
~
EXAMPLES of POKE Statement:
POKE 1024, 1 (Puts an "A" at position 1 on the screen)
POKE 2040, PTR (Updates Sprite #0 data pointer)
10 POKE RED,32
20 POKE 36879,8
2050 POKE A,B
POS
TYPE: Integer Function
FORMAT: POS (<dummy>)
Action: Tells you the current cursor position which, of course, is in
the range of 0 (leftmost character) though position 79 on an 80-character
logical screen line. Since the Commodore 64 has a 40-column screen, any
position from 40 through 79 will refer to the second screen line. The
dummy argument is ignored.
EXAMPLE of POS Function:
1000 IF POS(0)>38 THEN PRINT CHR$(13)
PRINT
TYPE: Statement
FORMAT: PRINT [<variable>][<,/;><variable>]...
Action: The PRINT statement is normally used to write data items to
the screen. However, the CMD statement may be used to re-direct that
output to any other device in the system. The <variable(s)> in the
output-list are expressions of any type. If no output-list is present, a
blank line is printed. The position of each printed item is determined by
the punctuation used to separate items in the output-list.
The punctuation characters that you can use are blanks, commas, or
semicolons. The 80-character logical screen line is divided into 8 print
zones of 10 spaces each. In the list of expressions, a comma causes the
next value to be printed at the beginning of the next zone. A semicolon
causes the next value to be printed immediately following the previous
value. However, there are two exceptions to this rule:
70 BASIC LANGUAGE VOCABULARY
~
1) Numeric items are followed by an added space.
2) Positive numbers have a space preceding them.
When you use blanks or no punctuation between string constants or
variable names it has the same effect as a semicolon. However, blanks
between a string and a numeric item or between two numeric items will
stop output without printing the second item.
If a comma or a semicolon is at the end of the output-list, the next
PRINT statement begins printing on the same line, and spaced accord-
ingly. If no punctuation finishes the list, a carriage-return and a line-
feed are printed at the end of the data. The next PRINT statement will
begin on the next line. If your output is directed to the screen and the
data printed is longer than 40 columns, the output is continued on the
next screen line.
There is no statement in BASIC with more variety than the PRINT
statement. There are so many symbols, functions, and parameters
associated with this statement that it might almost be considered as a
language of its own within BASIC; a language specially designed for
writing on the screen.
EXAMPLES of PRINT Statement:
1)
5 X = 5
10 PRINT -5*X,X-5,X+5,X^5
-25 0 10 3125
2)
5 X=9
10 PRINT X;"SQUARED IS";X*X;"AND";
20 PRINT X "CUBED IS" X^3
9 SQUARED IS 81 AND 9 CUBED IS 729
3)
90 AA$="ALPHA":BB$="BAKER":CC$="CHARLIE":DD$="DOG":EE$="ECHO"
100 PRINT AA$BB$;CC$ DD$,EE$
ALPHABAKERCHARLIEDOG ECHO
BASIC LANGUAGE VOCABULARY 71
~
Quote Mode
Once the quote mark <SHIFT+2> is typed, the cursor controls stop
operating and start displaying reversed characters which actually stand
for the cursor control you are hitting. This allows you to program these
cursor controls, because once the text inside the quotes is PRINTed they
perform their functions. The <INST/DEL> key is the only cursor control
not affected by "quote mode."
1. Cursor Movement
The cursor controls which can be "programmed" in quote mode are:
KEY APPEARS AS
<CLR/HOME>
<SHIFT+CLR/HOME>
<CRSR UP/DOWN>
<SHIFT+CRSR UP/DOWN>
<CRSR LEFT/RIGHT>
<SHIFT+CRSR LEFT/RIGHT>
If you wanted the word HELLO to PRINT diagonally from the upper left
corner of the screen, you would type:
PRINT"<HOME>H<DOWN>E<DOWN>L<DOWN>L<DOWN>O"
2. Reverse Characters
Holding down the <CTRL> key and hitting <9> will cause <R> to appear
inside the quotes. This will make all characters start printing in
reverse video (like a negative of a picture). To end the reverse printing
hit <CTRL+0>, or else PRINT a <RETURN> (CHR$(13)). (Just ending the PRINT
statement without a semicolon or comma will take care of this.)
3.Color Controls
Holding down the <CTRL> key or <C=> key with any of the 8 color keys
will make a special reversed character appear in the quotes. When the
character is PRINTed, then the color change will occur.
72 BASIC LANGUAGE VOCABULARY
~
KEY COLOR APPEARS AS
<CTRL+1> Black
<CTRL+2> White
<CTRL+3> Red
<CTRL+4> Cyan
<CTRL+5> Purple
<CTRL+6> Green
<CTRL+7> Blue
<CTRL+8> Yellow
<C=+1> Orange
<C=+2> Brown
<C=+3> Light Red
<C=+4> Grey 1
<C=+5> Grey 2
<C=+6> Light Green
<C=+7> Light Blue
<C=+8> Grey 3
If you wanted to PRINT the word HELLO in cyan and the word THERE
in white, type:
PRINT "<CTRL+4>HELLO <CTRL+2>THERE"
4. Insert Mode
The spaces created by using the <INST/DEL> key have some of the same
characteristics as quote mode. The cursor controls and color controls
show up as reversed characters. The only difference is in the <INST> and
<DEL>, which performs its normal function even in quote mode, now
BASIC LANGUAGE VOCABULARY 73
~
creates the <T>. And <INST>, which created a special character in quote
mode, inserts spaces normally.
Because of this, it is possible to create a PRINT statement containing
DELetes, which cannot be PRINTed in quote mode. Here is an example
of how this is done:
10 PRINT"HELLO"<DEL><INST><INST><DEL><DEL>P"
When the above line is RUN, the word displayed will be HELP, because
the last two letters are deleted and the P is put in their place.
+-----------------------------------------------------------------------+
| WARNING: The DELetes will work when LISTing as well as PRINTing, so |
| editing a line with these characters will be difficult. |
+-----------------------------------------------------------------------+
The "insert mode" condition is ended when the <RETURN> (or
<SHIFT+RETURN>) key is hit, or when as many characters have been typed as
spaces were inserted.
5. Other Special Characters
There are some other characters that can be PRINTed for special
functions, although they are not easily available from the keyboard. In
order to get these into quotes, you must leave empty spaces for them in
the line, hit <RETURN> or <SHIFT+RETURN>, and go back to the spaces with
the cursor controls. Now you must hit <RVS ON>, to start typing reversed
characters, and type the keys shown below:
Function Type Appears As
<SHIFT+RETURN> <SHIFT+M>
switch to lower case <N>
switch to upper case <SHIFT+N>
disable case-switching keys <H>
enable case-switching keys <I>
74 BASIC LANGUAGE VOCABULARY
~
The <SHIFT+RETURN> will work in the LISTing as well as PRINTing, so
editing will be almost impossible if this character is used. The LISTing
will also look very strange.
PRINT#
TYPE: I/O Statement
FORMAT: PRINT#<file-number>[<variable>][<,/;><variable>]...
Actions: The PRINT# statement is used to write data items to a logical
file. It must use the same number used to OPEN the file. Output goes to
the device-number used in the OPEN statement. The <variable> expressions
in the output-list can be of any type. The punctuation characters between
items are the same as with the PRINT statement and they can be used in
the same ways. The effects of punctuation are different in two
significant respects.
When PRINT# is used with tape files, the comma, instead of spacing
by print zones, has the same effect as a semicolon. Therefore, whether
blanks, commas, semicolons or no punctuation characters are used between
data items, the effect on spacing is the same. The data items are written
as a continuous stream of characters. Numeric items are followed by a
space and, if positive, are preceded by a space.
If no punctuation finishes the list, a carriage-return and a line-feed
are written at the end of the data. If a comma or semicolon terminates
the output-list, the carriage-return and line-feed are suppressed. Re-
gardless of the punctuation, the next PRINT# statement begins output in
the next available character position. The line-feed will act as a stop
when using the INPUT# statement, leaving an empty variable when the next
INPUT# is executed. The line-feed can be suppressed or compensated for as
shown in the examples below.
The easiest way to write more than one variable to a file on tape or
disk is to set a string variable to CHR$(13), and use that string in be-
tween all the other variables when writing the file.
BASIC LANGUAGE VOCABULARY 75
~
EXAMPLES of PRINT# Statement:
1)
10 OPEN 1,1,1,"TAPE FILE"
20 R$=CHR$(13) (By Changing the CHR$(13) to
30 PRINT#1,1;R$;2;R$;3;R$;4;R$;5 CHR$(44) you put a "," between
40 PRINT#1,6 each variable. CHR$(59) would
50 PRINT# 1,7 put a ";" between each variable.)
2)
10 CO$=CHR$(44):CR$=CHR$(13)
20 PRINT#1,"AAA"CO$"BBB", AAA,BBB CCCDDDEEE
"CCC";"DDD";"EEE"CR$ (carriage return)
"FFF"CR$; FFF(carriage return)
30 INPUT#1,A$,BCDE$,F$
3)
5 CR$=CHR$(13)
10 PRINT#2,"AAA";CR$;"BBB" (10 blanks) AAA
20 PRINT#2,"CCC"; BBB
(10 blanks)CCC
30 INPUT#2,A$,B$,DUMMY$,C$
READ
TYPE: Statement
FORMAT: READ <variable>[,<variable>]...
Action: The READ statement is used to fill variable names from con-
stants in DATA statements. The data actually read must agree with the
variable types specified or the BASIC error message ?SYNTAX ERROR will
result.(*) Variables in the DATA input-list must be separated by commas.
A single READ statement can access one or more DATA statements,
which will be accessed in order (see DATA), or several READ statements
can access the same DATA statement. If more READ statements are executed
than the number of elements in DATA statements(s) in the program, the
76 BASIC LANGUAGE VOCABULARY
~
BASIC error message ?OUT OF DATA is printed. If the number of variables
specified is fewer than the number of elements in the DATA statement(s),
subsequent READ statements will continue reading at the next data
element. (See RESTORE.)
+-----------------------------------------------------------------------+
| *NOTE: The ?SYNTAX ERROR will appear with the line number from the |
| DATA statement, NOT the READ statement. |
+-----------------------------------------------------------------------+
EXAMPLES of READ Statement:
110 READ A,B,C$
120 DATA 1,2,HELLO
100 FOR X=1 TO 10: READ A(X):NEXT
200 DATA 3.08, 5.19, 3.12, 3.98, 4.24
210 DATA 5.08, 5.55, 4.00, 3.16, 3.37
(Fills array items (line 1) in order of constants shown (line 5))
1 READ CITY$,STATE$,ZIP
5 DATA DENVER,COLORADO, 80211
REM
TYPE: Statement
FORMAT: REM [<remark>]
Action:The REM statement makes your programs more easily understood
when LISTed. It's a reminder to yourself to tell you what you had in
mind when you were writing each section of the program. For instance,
you might want to remember what a variable is used for, or some other
useful information. The REMark can be any text, word, or character
including the colon (:) or BASIC keywords.
The REM statement and anything following it on the same line-number
are ignored by BASIC, but REMarks are printed exactly as entered when
the program is listed. A REM statement can be referred to by a GOTO or
GOSUB statement, and the execution of the program will continue with
the next higher program line having executable statements.
BASIC LANGUAGE VOCABULARY 77
~
EXAMPLES of REM Statement:
10 REM CALCULATE AVERAGE VELOCITY
20 FOR X= 1 TO 20 :REM LOOP FOR TWENTY VALUES
30 SUM=SUM + VEL(X): NEXT
40 AVG=SUM/20
RESTORE
TYPE: Statement
FORMAT: RESTORE
Action: BASIC maintains an internal pointer to the next DATA constant
to be READ. This pointer can be reset to the first DATA constant in a
program using the RESTORE statement. The RESTORE statement can be
used anywhere in the program to begin re-READing DATA.
EXAMPLES of RESTORE Statement:
100 FOR X=1 TO 10: READ A(X): NEXT
200 RESTORE
300 FOR Y=1 TO 10: READ B(Y): NEXT
4000 DATA 3.08, 5.19, 3.12, 3.98, 4.24
4100 DATA 5.08, 5.55, 4.00, 3.16, 3.37
(Fills the two arrays with identical data)
10 DATA 1,2,3,4
20 DATA 5,6,7,8
30 FOR L= 1 TO 8
40 READ A: PRINT A
50 NEXT
60 RESTORE
70 FOR L= 1 TO 8
80 READ A: PRINT A
90 NEXT
78 BASIC LANGUAGE VOCABULARY
~
RETURN
TYPE: Statement
FORMAT: RETURN
Action: The RETURN statement is used to exit from a subroutine called
for by a GOSUB statement. RETURN restarts the rest of your program at
the next executable statement following the GOSUB. If you are nesting
subroutines, each GOSUB must be paired with at least one RETURN
statement. A subroutine can contain any number of RETURN statements,
but the first one encountered will exit the subroutine.
EXAMPLE of RETURN Statement:
10 PRINT"THIS IS THE PROGRAM"
20 GOSUB 1000
30 PRINT"PROGRAM CONTINUES"
40 GOSUB 1000
50 PRINT"MORE PROGRAM"
60 END
1000 PRINT"THIS IS THE GOSUB":RETURN
RIGHT$
TYPE: String Function
FORMAT: RIGHT$ (<string>,<numeric>)
Action: The RIGHT$ function returns a sub-string taken from the right-
most end of the <string> argument. The length of the sub-string is
defined by the <numeric> argument which can be any integer in the range
of 0 to 255. If the value of the numeric expression is zero, then a null
string ("") is returned. If the value you give in the <numeric> argument
is greater than the length of the <string> then the entire string is
returned.
EXAMPLE of RIGHT$ Function:
10 MSG$="COMMODORE COMPUTERS"
20 PRINT RIGHT$(MSG$,9)
RUN
COMPUTERS
BASIC LANGUAGE VOCABULARY 79
~
RND
TYPE: Floating-Point Function
FORMAT: RND (<numeric>)
Action: RND creates a floating-point random from 0.0 to 1.0. The
computer generates a sequence of random numbers by performing cal-
culations on a starting number, which in computer jargon is called a
seed. The RND function is seeded on system power-up. The <numeric>
argument is a dummy, except for its sign (positive, zero, or negative).
If the <numeric> argument is positive, the same "pseudorandom"
sequence of numbers is returned, starting from a given seed value. Dif-
ferent number sequences will result from different seeds, but any se-
quence is repeatable by starting from the same seed number. Having a
known sequence of "random" numbers is useful in testing programs.
If you choose a <numeric> argument of zero, then RND generates a
number directly from a free-running hardware clock (the system "jiffy
clock"). Negative arguments cause the RND function to be re-seeded
with each function call.
EXAMPLES of RND Function:
220 PRINT INT(RND(0)*50) (Return random integers 0-49)
100 X=INT(RND(1)*6)+INT(RND(1)*6)+2 (Simulates 2 dice)
100 X=INT(RND(1)*1000)+1 (Random integers from 1-1000)
100 X=INT(RND(1)*150)+100 (Random numbers from 100-249)
100 X=RND(1)*(U-L)+L (Random numbers between
upper (U) and lower (L) limits)
80 BASIC LANGUAGE VOCABULARY
~
RUN
TYPE: Command
FORMAT: RUN [<line-number>]
Action: The system command RUN is used to start the program currently
in memory. The RUN command causes an implied CLR operation to be
performed before starting the program. You can avoid the CLeaRing
operation by using CONT or GOTO to restart a program instead of RUN. If
a <line-number> is specified, your program will start on that line.
Otherwise, the RUN command starts at first line of the program. The RUN
command can also be used within a program. If the <line-number> you
specify doesn't exist, the BASIC error message UNDEF'D STATEMENT occurs.
A RUNning program stops and BASIC returns to direct mode when an END or
STOP statement is reached, when the last line of the program is finished,
or when a BASIC error occurs during execution.
EXAMPLES of RUN Command:
RUN (Starts at first line of program)
RUN 500 (Starts at line-number 500)
RUN X (Starts at line X, or UNDEF'D STATEMENT ERROR
if there is no line X)
SAVE
TYPE: Command
FORMAT: SAVE ["<file-name>"][,<device-number>][,<address>]
Action: The SAVE command is used to store the program that is cur-
rently in memory onto a tape or diskette file. The program being SAVED
is only affected by the command while the SAVE is happening. The program
remains in the current computer memory even after the SAVE operation is
completed until you put something else there by using another command.
The file type will be "prg" (program). If the <device-number> is left
out, then the C64 will automatically assume that you want the program
saved on cassette, device number 1. If the <device-number> is an <8>,
then the program is written onto disk. The SAVE statement can be used
BASIC LANGUAGE VOCABULARY 81
~
be used in your programs and execution will continue with the next
statement after the SAVE is completed.
Programs on tape are automatically stored twice, so that your Com-
modore 64 can check for errors when LOADing the program back in. When
saving programs to tape, the <file-name> and secondary <address> are
optional. But following a SAVE with a program name in quotes ("") or
by a string variable (---$) helps your Commodore 64 find each program
more easily. If the file-name is left out it can NOT be LOADed by name
later on.
A secondary address of I will tell the KERNAL to LOAD the tape at a
later time, with the program currently in memory instead of the normal
2048 location. A secondary address of 2 will cause an end-of-tape marker
to follow the program. A secondary address of 3 combines both functions.
When saving programs onto a disk, the <file-name> must be present.
EXAMPLES of SAVE Command.
SAVE (Write to tape without a name)
SAVE"ALPHA",1 (Store on tape as file-name "alpha")
SAVE"ALPHA",1,2 (Store "alpha" with end-of-tape marker)
SAVE"FUN.DISK",8 (SAVES on disk (device 8 is the disk))
SAVE A$ (Store on tape with the name A$)
10 SAVE"HI" (SAVEs program and then move to next program line)
SAVE"ME",1,3 (Stores at same memory location and puts an
end-of-tope marker on)
82 BASIC LANGUAGE VOCABULARY
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SGN
TYPE: Integer Function
FORMAT: SGN (<numeric>)
Action: SGN gives you an integer value depending upon the sign of the
<numeric> argument. If the argument is positive the result is 1, if zero
the result is also 0, if negative the result is -1.
EXAMPLE of SGN Function:
90 ON SGN(DV)+2 GOTO 100, 200, 300
(jump to 100 if DV=negative, 200 if DV=0, 300 if DV=positive)
SIN
TYPE: Floating-Point Function
FORMAT: SIN (<numeric>)
Action: SIN gives you the sine of the <numeric> argument, in radians.
The value of COS(X) is equal to SIN(x+3.14159265/2).
EXAMPLE of SIN Function:
235 AA=SIN(1.5):PRINT AA
.997494987
SPC
TYPE: String Function
FORMAT: SPC (<numeric>)
Action: The SPC function is used to control the formatting of data, as
either an output to the screen or into a logical file. The number of
SPaCes given by the <numeric> argument are printed, starting at the first
available position. For screen or tape files the value of the argument
is in the range of 0 to 255 and for disk files up to 254. For printer
files, an automatic carriage-return and line-feed will be performed by
the printer if a SPaCe is printed in the last character position of a
line. No SPaCes are printed on the following line.
BASIC LANGUAGE VOCABULARY 83
~
EXAMPLE of SPC Function:
10 PRINT"RIGHT "; "HERE &";
20 PRINT SPC(5)"OVER" SPC(14)"THERE"
RUN
RIGHT HERE & OVER THERE
SQR
TYPE: Floating-Point Function
FORMAT: SQR (<numeric>)
Action: SQR gives you the value of the SQuare Root of the <numeric>
argument. The value of the argument must not be negative, or the BASIC
error message ?ILLEGAL QUANTITY will happen.
EXAMPLE of SQR Function:
FOR J = 2 TO 5: PRINT J*S, SQR(J*5): NEXT
10 3.16227766
15 3.87298335
20 4.47213595
25 5
READY
STATUS
TYPE: Integer Function
FORMAT: STATUS
Action: Returns a completion STATUS for the last input/output operation
which was performed on an open file. The STATUS can be read from any
peripheral device. The STATUS (or simply ST) keyword is a system defined
84 BASIC LANGUAGE VOCABULARY
~
variable-name into which the KERNAL puts the STATUS of I/O operations.
A table of STATUS code values for tape, printer, disk and RS-232 file
operations is shown below:
+---------+------------+---------------+------------+-------------------+
| ST Bit | ST Numeric | Cassette | Serial | Tape Verify |
| Position| Value | Read | Bus R/W | + Load |
+---------+------------+---------------+------------+-------------------+
| 0 | 1 | | time out | |
| | | | write | |
+---------+------------+---------------+------------+-------------------+
| 1 | 2 | | time out | |
| | | | read | |
+---------+------------+---------------+------------+-------------------+
| 2 | 4 | short block | | short block |
+---------+------------+---------------+------------+-------------------+
| 3 | 8 | long block | | long block |
+---------+------------+---------------+------------+-------------------+
| 4 | 16 | unrecoverable | | any mismatch |
| | | read error | | |
+---------+------------+---------------+------------+-------------------+
| 5 | 32 | checksum | | checksum |
| | | error | | error |
+---------+------------+---------------+------------+-------------------+
| 6 | 64 | end of file | EOI | |
+---------+------------+---------------+------------+-------------------+
| 7 | -128 | end of tape | device not | end of tape |
| | | | present | |
+---------+------------+---------------+------------+-------------------+
EXAMPLES of STATUS Function:
10 OPEN 1,4:OPEN 2,8,4,"MASTER FILE,SEQ,W"
20 GOSUB 100:REM CHECK STATUS
30 INPUT#2,A$,B,C
40 IF STATUS AND 64 THEN 80:REM HANDLE END-OF-FILE
50 GOSUB 100:REM CHECK STATUS
60 PRINT#1,A$,B;C
70 GOTO 20
80 CLOSE1:CLOSE2
90 GOSUB 100:END
100 IF ST > 0 THEN 9000:REM HANDLE FILE I/O ERROR
110 RETURN
BASIC LANGUAGE VOCABULARY 85
~
STEP
TYPE: Statement
FORMAT: [STEP <expression>]
Action: The optional STEP keyword follows the <end-value> expression in
a FOR statement. It defines an increment value for the loop counter
variable. Any value can be used as the STEP increment. Of course, a STEP
value of zero will loop forever. If the STEP keyword is left out, the
increment value will be + 1. When the NEXT statement in a FOR loop is
reached, the STEP increment happens. Then the counter is tested against
the end-value to see if the loop is finished. (See FOR statement for more
information.)
+-----------------------------------------------------------------------+
| NOTE: The STEP value can NOT be changed once it's in the loop. |
+-----------------------------------------------------------------------+
EXAMPLES of STEP Statement:
25 FOR XX=2 TO 20 STEP 2 (Loop repeats 10 times)
35 FOR ZZ=0 TO -20 STEP -2 (Loop repeats 11 times)
STOP
TYPE: Statement
FORMAT: STOP
Action: The STOP statement is used to halt execution of the current
program and return to direct mode. Typing the <RUN/STOP> key on the
keyboard has the same effect as a STOP statement. The BASIC error message
?BREAK IN LINE nnnnn is displayed on the screen, followed by READY. The
"nnnnn" is the line-number where the STOP occurs. Any open files remain
open and all variables are preserved and can be examined. The program can
be restarted by using CONT or GOTO statements.
EXAMPLES of STOP Statement:
10 INPUT#1,AA,BB,CC
20 IF AA=BB AND BB=CC THEN STOP
30 STOP
(If the variable AA is -1 and BB is equal to CC then:)
BREAK IN LINE 20
BREAK IN LINE 30 (For any other data values)
86 BASIC LANGUAGE VOCABULARY
~
STR$
TYPE: String Function
FORMAT: STR$ (<numeric>)
Action: STR$ gives you the STRing representation of the numeric value
of the argument. When the STR$ value is converted to each variable
represented in the <numeric> argument, any number shown is followed by
a space and, if it's positive, it is also preceded by a space.
EXAMPLE of STR$ Function:
100 FLT = 1.5E4: ALPHA$ = STR$(FLT)
110 PRINT FLT, ALPHA$
15000 15000
SYS
TYPE: Statement
FORMAT: SYS <memory-location>
Action: This is the most common way to mix a BASIC program with a
machine language program. The machine language program begins at the
location given in the SYS statement. The system command SYS is used in
either direct or program mode to transfer control of the microprocessor
to an existing machine language program in memory. The memory-location
given is by numeric expression and can be anywhere in memory, RAM or ROM.
When you're using the SYS statement you must end that section of
machine language code with an RTS (ReTurn from Subroutine) instruction
so that when the machine language program is finished, the BASIC
execution will resume with the statement following the SYS command.
EXAMPLES of SYS Statement:
SYS 64738 (Jump to System Cold Start in ROM)
10 POKE 4400,96:SYS 4400 (Goes to machine code location 4400
and returns immediately)
BASIC LANGUAGE VOCABULARY 87
~
TAB
TYPE: String Function
FORMAT: TAB (<numeric>)
Action: The TAB function moves the cursor to a relative SPC move
position on the screen given by the <numeric> argument, starting with
the left-most position of the current line. The value of the argument can
range from 0 to 255. The TAB function should only be used with the PRINT
statement, since it has no effect if used with PRINT# to a logical
file.
EXAMPLE of TAB Function:
100 PRINT"NAME" TAB(25) "AMOUNT": PRINT
110 INPUT#1, NAM$, AMT$
120 PRINT NAM$ TAB(25) AMT$
NAME AMOUNT
G.T. JONES 25.
TAN
TYPE: Floating-Point Function
FORMAT: TAN (<numeric>)
Action: Returns the tangent of the value of the <numeric> expression
in radians. If the TAN function overflows, the BASIC error message
?DIVISION BY ZERO is displayed.
EXAMPLE of TAN Function:
10 XX=.785398163: YY=TAN(XX):PRINT YY
1
88 BASIC LANGUAGE VOCABULARY
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TIME
TYPE: Numeric Function
FORMAT: TI
Action: The TI function reads the interval Timer. This type of "clock"
is called a "jiffy clock." The "jiffy clock" value is set at zero
(initialized) when you power-up the system. This 1/60 second interval
timer is turned off during tape I/O.
EXAMPLE of TI Function:
10 PRINT TI/60 "SECONDS SINCE POWER UP"
TIME$
TYPE: String Function
FORMAT: TI$
Action: The TI$ timer looks and works like a real clock as long as your
system is powered-on. The hardware interval timer (or jiffy clock) is
read and used to update the value of TI$, which will give you a TIme
$tring of six characters in hours, minutes and seconds. The TI$ timer can
also be assigned an arbitrary starting point similar to the way you set
your wristwatch. The value of TI$ is not accurate after tape I/O.
EXAMPLE of TI$ Function:
1 TI$ = "000000": FOR J=1 TO 10000: NEXT: PRINT TI$
000011
BASIC LANGUAGE VOCABULARY 89
~
USR
TYPE: Floating-Point Function
FORMAT: USR (<numeric>)
Action: The USR function jumps to a User callable machine language
SubRoutine which has its starting address pointed to by the contents of
memory locations 785-786. The starting address is established before
calling the USR function by using POKE statements to set up locations
785-786. Unless POKE statements are used, locations 785-786 will give
you an ?ILLEGAL QUANTITY error message.
The value of the <numeric> argument is stored in the floating-point
accumulator starting at location 97, for access by the Assembler code,
and the result of the USR function is the value which ends up there when
the subroutine returns to BASIC.
EXAMPLES of USR Function:
10 B=T*SIN(Y)
20 C=USR(B/2)
30 D=USR(B/3)
VAL
TYPE: Numeric Function
FORMAT: VAL (<string>)
Action: Returns a numeric VALue representing the data in the <string>
argument. If the first non-blank character of the string is not a plus
sign (+), minus sign (-), or a digit the VALue returned is zero. String
conversion is finished when the end of the string or any non-digit
character is found (except decimal point or exponential e).
EXAMPLE of VAL Function:
10 INPUT#1, NAM$, ZIP$
20 IF VAL(ZIP$) < 19400 OR VAL(ZIP$) > 96699
THEN PRINT NAM$ TAB(25) "GREATER PHILADELPHIA"
90 BASIC LANGUAGE VOCABULARY
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VERIFY
TYPE: Command
FORMAT: VERIFY ["<file-name>"][,<device>]
Action: The VERIFY command is used, in direct or program mode, to compare
the contents of a BASIC program file on tape or disk with the program
currently in memory. VERIFY is normally used right after a SAVE, to make
sure that the program was stored correctly on tape or disk.
If the <device> number is left out, the program is assumed to be on
the Datassette(TM) which is device number 1. For tape files, if the
<file-name> is left out, the next program found on the tape will be com-
pared. For disk files (device number 8), the file-name must be present.
If any differences in program text are found, the BASIC error message
?VERIFY ERROR is displayed.
A program name can be given either in quotes or as a string variable.
VERIFY is also used to position a tape just past the last program, so
that a new program can be added to the tape without accidentally writing
over another program.
EXAMPLES of VERIFY Command:
VERIFY (Checks 1st program on tape)
PRESS PLAY ON TAPE
OK
SEARCHING
FOUND <FILENAME>
VERIFYING
9000 SAVE "ME",8:
9010 VERIFY "ME",8 (Looks at device 8 for the program)
BASIC LANGUAGE VOCABULARY 91
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WAIT
TYPE: Statement
FORMAT: WAIT <location>,<mask-1>[,<mask-2>]
Action: The WAIT statement causes program execution to be suspended
until a given memory address recognizes a specified bit pattern. In other
words WAIT can be used to halt the program until some external event has
occurred. This is done by monitoring the status of bits in the input/
output registers, The data items used with WAIT can be any numeric
expressions, but they will be converted to integer values. For most
programmers, this statement should never be used. It causes the program
to halt until a specific memory location's bits change in a specific way.
This is used for certain I/O operations and almost nothing else.
The WAIT statement takes the value in the memory location and performs
a logical AND operation with the value in mask-1. If there is a mask-2 in
the statement, the result of the first operation is exclusive-ORed with
mask-2. In other words mask-1 "filters out" any bits that you don't want
to test. Where the bit is 0 in mask-1, the corresponding bit in the
result will always be 0. The mask-2 value flips any bits, so that you
can test for an off condition as well as an on condition, Any bits being
tested for a 0 should have a I in the corresponding position in mask-2.
If corresponding bits of the <mask-1> and <mask-2> operands differ, the
exclusive-OR operation gives a bit result of 1. If corresponding bits get
the same result the bit is 0. It is possible to enter an infinite pause
with the WAIT statement, in which case the <RUN/STOP> and <RESTORE> keys
can be used to recover. Hold down the <RUN/STOP> key and then press
<RESTORE>. The first example below WAITs until a key is pressed on the
tape unit to continue with the program. The second example will WAIT
until a sprite collides with the screen background.
EXAMPLES of WAIT Statement:
WAIT 1,32,32
WAIT 53273,6,6
WAIT 36868,144,16 (144 & 16 are masks. 144=10010000 in binary
and 16=10000 in binary. The WAIT statement
will halt the program until the 128 bit is
on or until the 16 bit is off)
92 BASIC LANGUAGE VOCABULARY
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THE COMMODORE 64 KEYBOARD
AND FEATURES
The Operating System has a ton-character keyboard "buffer" that is used
to hold incoming keystrokes until they can be processed. This buffer, or
queue, holds keystrokes in the order in which they occur so that the
first one put into the queue is the first one processed. For example, if
a second keystroke occurs before the first can be processed, the second
character Is stored in the buffer, while processing of the first
character continues. After the program has finished with the first
character, the keyboard buffer is examined for more data, and the second
keystroke processed. Without this buffer, rapid keyboard input would
occasionally drop characters.
In other words, the keyboard buffer allows you to "type-ahead" of the
system, which means it can anticipate responses to INPUT prompts or GET
statements. As you type on the keys their character values are lined up,
single-file (queued) into the buffer to wait for processing in the order
the keys were struck. This type-ahead feature can give you an occasional
problem where an accidental keystroke causes a program to fetch an
incorrect character from the buffer.
Normally, incorrect keystrokes present no problem, since they can be
corrected by the CuRSoR-Left <CRSR LEFT> or DELete <INST/DEL> keys and
then retyping the character, and the corrections will be processed before
a following carriage-return. However, if you press the <RETURN> key, no
corrective action is possible, since all characters in the buffer up to
and including the carriage-return will be processed before any cor-
rections. This situation can be avoided by using a loop to empty the
keyboard buffer before reading an intended response:
10 GET JUNK$: IF JUNK$ <>"" THEN 10: REM EMPTY THE KEYBOARD BUFFER
In addition to GET and INPUT, the keyboard can also be read using
PEEK to fetch from memory location 197 ($00C5) the integer value of the
key currently being pressed. If no key Is being held when the PEEK is
executed, a value of 64 is returned, The numeric keyboard values,
keyboard symbols and character equivalents (CHR$) are shown in Ap-
pendix C. The following example loops until a key is pressed then con-
verts the integer to a character value.
10 AA=PEEK(197): IF AA=64 THEN 10
20 BB$=CHR$(AA)
BASIC LANGUAGE VOCABULARY 93
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The keyboard is treated as a set of switches organized into a matrix
of 8 columns by 8 rows. The keyboard matrix is scanned for key switch-
closures by the KERNAL using the CIA #l 1/0 chip (MOS 6526 Complex
Interface Adapter). Two CIA registers are used to perform the scan:
register #0 at location 56320 ($DC00) for keyboard columns and
register #l at location 56321 ($DC01) for keyboard rows.
Bits 0-7 of memory location 56320 correspond to the columns 0-7. Bits
0-7 of memory location 56321 correspond to rows 0-7. By writing column
values in sequence, then reading row values, the KERNAL decodes the
switch closures into the CHR$ (N) value of the key pressed.
Eight columns by eight rows yields 64 possible values. However, if you
first strike the <RVS ON>, <CTRL> or <C=> keys or hold down the <SHIFT>
key and type a second character, additional values are generated. This is
because the KERNAL decodes these keys separately and "remembers" when one
of the control keys was pressed. The result of the keyboard scan is then
placed in location 197.
Characters can also be written directly to the keyboard buffer at lo-
cations 631-640 using a POKE statement. These characters will be
processed when the POKE is used to set a character count into location
198. These facts can be used to cause a series of direct-mode commands to
be executed automatically by printing the statements onto the screen,
putting carriage-returns into the buffer, and then setting the character
count. In the example below, the program will LIST itself to the printer
and then resume execution.
10 PRINT CHR$(147)"PRINT#1: CLOSE 1: GOTO 50"
20 POKE 631119: POKE 632,13: POKE 633,13: POKE 198,3
30 OPEN 114: CMD1: LIST
40 END
50 REM PROGRAM RE-STARTS HERE
SCREEN EDITOR
The SCREEN EDITOR provides you with powerful and convenient facilities
for editing program text. Once a section of a program is listed to the
screen, the cursor keys and other special keys are used to move around
the screen so that you can make any appropriate changes. After making all
the changes you want to a specific line-number of text, hitting the
<RETURN> key anywhere on the line, causes the SCREEN EDITOR to read the
entire 80-character logical screen line.
94 BASIC LANGUAGE VOCABULARY
~
The text is then passed to the Interpreter to be tokenized and stored
in the program. The edited line replaces the old version of that line in
memory. An additional copy of any line of text can be created simply by
changing the line-number and pressing <RETURN>.
If you use keyword abbreviations which cause a program line to exceed
80 characters, the excess characters will be lost when that line is
edited, because the EDITOR will read only two physical screen lines. This
is also why using INPUT for more than a total of 80 characters is not
possible. Thus, for all practical purposes, the length of a line of BASIC
text is limited to 80 characters as displayed on the screen.
Under certain conditions the SCREEN EDITOR treats the cursor control
keys differently from their normal mode of handling. If the CuRSoR is
positioned to the right of an odd number of double-quote marks (") the
EDITOR operates in what is known as the QUOTE-MODE.
In quote mode data characters are entered normally but the cursor
controls no longer move the CuRSoR, instead reversed characters are
displayed which actually stand for the cursor control being entered. The
same is true of the color control keys. This allows you to include cursor
and color controls inside string data items in programs. You will find
that this is a very important and powerful feature. That's because when
the text inside the quotes is printed to the screen it performs the
cursor positioning and color control functions automatically as part of
the string. An example of using cursor controls in strings is:
You type --> 10 PRINT"A(R)(R)B(L)(L)(L)C(R)(R)D": REM(R)=CRSR
RIGHT, (L)=CRSR LEFT
Computer prints --> AC BD
The <DEL> key is the only cursor control NOT affected by quote mode.
Therefore, if an error is made while keying in quote mode, the
<CRSR LEFT> key can't be used to back up and strike over the error -
even the <INST> key produces a reverse video character. Instead, finish
entering the line, and then, after hitting the <RETURN> key, you can
edit the line normally. Another alternative, if no further cursor-
controls are needed in the string, is to press the <RUN/STOP> and
<RESTORE> keys which will cancel QUOTE MODE. The cursor control keys
that you can use in strings are shown in Table 2-2.
BASIC LANGUAGE VOCABULARY 95
~
Table 2-2. Cursor Control Characters in QUOTE MODE
-------------------------------------------------------------------------
Control Key Appearance
-------------------------------------------------------------------------
CRSR up
CRSR down
CRSR left
CRSR right
CLR
HOME
INST
-------------------------------------------------------------------------
When you are NOT in quote mode, holding down the <SHIFT> key and then
pressing the INSerT <INST> key shifts data to the right of the cursor to
open up space between two characters for entering data between them. The
Editor then begins operating in INSERT MODE until all of the space opened
up is filled.
The cursor controls and color controls again show as reversed char-
acters in insert mode. The only difference occurs on the DELete and
INSerT <INST/DEL> key. The <DEL> instead of operating normally as in
the quote mode, now creates the reversed <T>. The <INST> key, which
created a reverse character in quote mode, inserts spaces normally.
This means that a PRINT statement can be created, containing DELetes,
which can't be done in quote mode. The insert mode is cancelled by
pressing the <RETURN>, <SHIFT> and <RETURN>, or <RUN/STOP> and <RESTORE>
keys. Or you can cancel the insert mode by filling all the inserted
spaces. An example of using DEL characters in strings is:
10 PRINT"HELLO"<DEL><INST><INST><DEL><DEL>P"
(Keystroke sequence shown above, appearance when listed below)
10 PRINT"HELP"
When the example is RUN, the word displayed will be HELP, because the
letters LO are deleted before the P is printed. The DELete character in
strings will work with LIST as well as PRINT. You can use this to "hide"
part or all of a line of text using this technique. However, trying to
edit a line with these characters will be difficult if not impossible.
96 BASIC LANGUAGE VOCABULARY
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There are some other characters that can be printed for special func-
tions, although they are not easily available from the keyboard. In order
to get these into quotes, you must leave empty spaces for them in the
line, press <RETURN>, and go back to edit the line. Now you hold down
the <CTRL> (ConTRoL) key and type <RVS ON> (ReVerSe-ON) to start typing
reversed characters. Type the keys as shown below:
Key Function Key Entered Appearance
Shifted RETURN <SHIFT+M>
Switch to upper/lower case <N>
Switch to upper/graphics <SHIFT+N>
Holding down the <SHIFT> key and hitting <RETURN> causes a carriage-
return and line-feed on the screen but does not end the string. This
works with LIST as well as PRINT, so editing will be almost impossible if
this character is used. When output is switched to the printer via the
CMD statement, the reverse "N" character shifts the printer into its
upper-lower case character set and the <SHIFT> "N" shifts the printer
into the upper-case/graphics character set.
Reverse video characters can be included in strings by holding down
the ConTRoL <CTRL> key and pressing ReVerSe <RVS>, causing a reversed R
to appear inside the quotes. This will make all characters print in
reverse video (like a negative of a photograph). To end the reverse
printing, press <CTRL> and <RVS OFF> (ReVerSe OFF) by holding down the
<CTRL> key and typing the <RVS OFF> key, which prints a reverse R.
Numeric data can be printed in reverse video by first printing a
CHR$(18). Printing a CHR$(146) or a carriage-return will cancel reverse
video output.
BASIC LANGUAGE VOCABULARY 97
~~
CHAPTER 3
PROGRAMMING
GRAPHICS
ON THE
COMMODORE 64
o Graphics Overview
o Graphics Locations
o Standard Character Mode
o Programmable Characters
o Multi-Color Mode Graphics
o Extended Background Color Mode
o Bit Mapped Graphics
o Multi-Color Bit Map Mode
o Smooth Scrolling
o Sprites
o Other Graphics Features
o Programming Sprites -
Another Look
99
~
GRAPHICS OVERVIEW
All of the graphics abilities of the Commodore 64 come from the 6567
Video Interface Chip (also known as the VIC-II chip). This chip gives a
variety of graphics modes, including a 40 column by 25 line text display,
a 320 by 200 dot high resolution display, and SPRITES, small movable
objects which make writing games simple. And if this weren't enough,
many of the graphics modes can be mixed on the same screen. It is
possible, for example, to define the top half of the screen to be in
high resolution mode, while the bottom half is in text mode. And SPRITES
will combine with anything! More on sprites later. First the other
graphics modes.
The VIC-II chip has the following graphics display modes:
A) CHARACTER DISPLAY MODES
1) Standard Character Mode
a)ROM characters
b)RAM programmable characters
2) Multi-Color Character Mode
a)ROM characters
b)RAM programmable characters
3) Extended Background Color Mode
a)ROM characters
b)RAM programmable characters
B) BIT MAP MODES
1) Standard Bit Map Mode
2) Multi-Color Bit Map Mode
C) SPRITES
1) Standard Sprites
2) Multi-Color Sprites
100 PROGRAMMING GRAPHICS
~
GRAPHICS LOCATIONS
Some general information first. There are 1000 possible locations on
the Commodore 64 screen. Normally, the screen starts at location 1024
($0400 in HEXadecimal notation) and goes to location 2023. Each of
these locations is 8 bits wide. This means that it can hold any integer
number from 0 to 255. Connected with screen memory is a group of 1000
locations called COLOR MEMORY or COLOR RAM. These start at location 55296
($D800 in HEX) and go up to 56295. Each of the color RAM locations is 4
bits wide, which means that it can hold any integer number from 0 to 15.
Since there are 16 possible colors that the Commodore 64 can use, this
works out well.
In addition, there are 256 different characters that can be displayed
at any time. For normal screen display, each of the 1000 locations in
screen memory contains a code number which tells the VIC-II chip which
character to display at that screen location.
The various graphics modes are selected by the 47 CONTROL registers in
the VIC-II chip. Many of the graphics functions can be controlled by
POKEing the correct value into one of the registers. The VIC-II chip is
located starting at 53248 ($D000 in HEX) through 53294 ($D02E in HEX).
VIDEO BANK SELECTION
The VIC-II chip can access ("see") 16K of memory at a time. Since there
is 64K of memory in the Commodore 64, you want to be able to have the
VIC-II chip see all of it. There is a way. There are 4 possible BANKS
(or sections) of 16K of memory. All that is needed is some means of
controlling which 16K bank the VIC-II chip looks at. In that way, the
chip can "see" the entire 64K of memory. The BANK SELECT bits that allow
you access to all the different sections of memory are located in the
6526 COMPLEX INTERFACE ADAPTER CHIP #2 (CIA #2). The POKE and PEEK BASIC
statements (or their machine language versions) are used to select a
bank, by controlling bits 0 and 1 of PORT A of CIA#2 (location 56576 (or
$DD00 HEX)). These 2 bits must be set to outputs by setting bits 0 and 1
of location 56578 ($DD02,HEX) to change banks. The following example
shows this:
POKE 56578,PEEK(56578)OR 3: REM MAKE SURE BITS 0 AND 1 ARE OUTPUTS
POKE 56576,(PEEK(56576)AND 252)OR A: REM CHANGE BANKS
"A" should have one of the following values:
PROGRAMMING GRAPHICS 101
~
+-------+------+-------+----------+-------------------------------------+
| VALUE | BITS | BANK | STARTING | VIC-II CHIP RANGE |
| OF A | | | LOCATION | |
+-------+------+-------+----------+-------------------------------------+
| 0 | 00 | 3 | 49152 | ($C000-$FFFF)* |
| 1 | 01 | 2 | 32768 | ($8000-$BFFF) |
| 2 | 10 | 1 | 16384 | ($4000-$7FFF)* |
| 3 | 11 | 0 | 0 | ($0000-$3FFF) (DEFAULT VALUE) |
+-------+------+-------+----------+-------------------------------------+
This 16K bank concept is part of everything that the VIC-II chip does.
You should always be aware of which bank the VIC-II chip is pointing at,
since this will affect where character data patterns come from, where the
screen is, where sprites come from, etc. When you turn on the power of
your Commodore 64, bits 0 and 1 of location 56576 are automatically set
to BANK 0 ($0000-$3FFF) for all display information.
+-----------------------------------------------------------------------+
| *NOTE: The Commodore 64 character set is not available to the VIC-II |
| chip in BANKS 1 and 3. (See character memory section.) |
+-----------------------------------------------------------------------+
SCREEN MEMORY
The location of screen memory can be changed easily by a POKE to
control register 53272 ($D018 HEX). However, this register is also used
to control which character set is used, so be careful to avoid disturbing
that part of the control register. The UPPER 4 bits control the location
of screen memory. To move the screen, the following statement should be
used:
POKE53272,(PEEK(53272)AND15)OR A
102 PROGRAMMING GRAPHICS
~
Where "A" has one of the following values:
+---------+------------+-----------------------------+
| | | LOCATION* |
| A | BITS +---------+-------------------+
| | | DECIMAL | HEX |
+---------+------------+---------+-------------------+
| 0 | 0000XXXX | 0 | $0000 |
| 16 | 0001XXXX | 1024 | $0400 (DEFAULT) |
| 32 | 0010XXXX | 2048 | $0800 |
| 48 | 0011XXXX | 3072 | $0C00 |
| 64 | 0100XXXX | 4096 | $1000 |
| 80 | 0101XXXX | 5120 | $1400 |
| 96 | 0110XXXX | 6144 | $1800 |
| 112 | 0111XXXX | 7168 | $1C00 |
| 128 | 1000XXXX | 8192 | $2000 |
| 144 | 1001XXXX | 9216 | $2400 |
| 160 | 1010XXXX | 10240 | $2800 |
| 176 | 1011XXXX | 11264 | $2C00 |
| 192 | 1100XXXX | 12288 | $3000 |
| 208 | 1101XXXX | 13312 | $3400 |
| 224 | 1110XXXX | 14336 | $3800 |
| 240 | 1111XXXX | 15360 | $3C00 |
+---------+------------+---------+-------------------+
+-----------------------------------------------------------------------+
| * Remember that the BANK ADDRESS of the VIC-II chip must be added in. |
| You must also tell the KERNAL'S screen editor where the screen is as |
| follows: POKE 648, page (where page = address/256, e.g., 1024/256= 4, |
| so POKE 648,4). |
+-----------------------------------------------------------------------+
COLOR MEMORY
Color memory can NOT move. It is always located at locations 55296
($D800) through 56295 ($DBE7). Screen memory (the 1000 locations starting
at 1024) and color memory are used differently in the different graphics
modes. A picture created in one mode will often look completely different
when displayed in another graphics mode.
CHARACTER MEMORY
Exactly where the VIC-II gets it character information is important to
graphic programming. Normally, the chip gets the shapes of the characters
PROGRAMMING GRAPHICS 103
~
you want to be displayed from the CHARACTER GENERATOR ROM. In this chip
are stored the patterns which make up the various letters, numbers,
punctuation symbols, and the other things that you see on the keyboard.
One of the features of the Commodore 64 is the ability to use patterns
located in RAM memory. These RAM patterns are created by you, and that
means that you can have an almost infinite set of symbols for games,
business applications, etc.
A normal character set contains 256 characters in which each character
is defined by 8 bytes of data. Since each character takes up 8 bytes this
means that a full character set is 256*8=2K bytes of memory. Since the
VIC-II chip looks at 16K of memory at a time, there are 8 possible
locations for a complete character set. Naturally, you are free to use
less than a full character set. However, it must still start at one of
the 8 possible starting locations.
The location of character memory is controlled by 3 bits of the VIC-II
control register located at 53272 ($D018 in HEX notation). Bits 3,2, and
1 control where the characters' set is located in 2K blocks. Bit 0 is ig-
nored. Remember that this is the same register that determines where
screen memory is located so avoid disturbing the screen memory bits. To
change the location of character memory, the following BASIC statement
can be used:
POKE 53272,(PEEK(53272)AND240)OR A
Where A is one of the following values:
+-----+----------+------------------------------------------------------+
|VALUE| | LOCATION OF CHARACTER MEMORY* |
| of A| BITS +-------+----------------------------------------------+
| | |DECIMAL| HEX |
+-----+----------+-------+----------------------------------------------+
| 0 | XXXX000X | 0 | $0000-$07FF |
| 2 | XXXX001X | 2048 | $0800-$0FFF |
| 4 | XXXX010X | 4096 | $1000-$17FF ROM IMAGE in BANK 0 & 2 (default)|
| 6 | XXXX011X | 6144 | $1800-$1FFF ROM IMAGE in BANK 0 & 2 |
| 8 | XXXX100X | 8192 | $2000-$27FF |
| 10 | XXXX101X | 10240 | $2800-$2FFF |
| 12 | XXXX110X | 12288 | $3000-$37FF |
| 14 | XXXX111X | 14336 | $3800-$3FFF |
+-----+----------+-------+----------------------------------------------+
+-----------------------------------------------------------------------+
| * Remember to add in the BANK address. |
+-----------------------------------------------------------------------+
104 PROGRAMMING GRAPHICS
~
The ROM IMAGE in the above table refers to the character generator ROM.
It appears in place of RAM at the above locations in bank 0. it also
appears in the corresponding RAM at locations 36864-40959 ($9000-$9FFF)
in bank 2. Since the VIC-II chip can only access 16K of memory at a time,
the ROM character patterns appear in the 16K block of memory the VIC-II
chip looks at. Therefore, the system was designed to make the VIC-II chip
think that the ROM characters are at 4096-8191 ($1000-$1FFF) when your
data is in bank 0, and 36864-40959 ($9000-$9FFF) when your data is in
bank 2, even though the character ROM is actually at location 53248-57343
($D000-$DFFF). This imaging only applies to character data as seen by the
VIC-II chip. It can be used for programs, other data, etc., just like any
other RAM memory.
+-----------------------------------------------------------------------+
| NOTE: If these ROM images got in the way of your own graphics, then |
| set the BANK SELECT BITS to one of the BANKS without the images |
| (BANKS 1 or 3). The ROM patterns won't be there. |
+-----------------------------------------------------------------------+
The location and contents of the character set in ROM are as follows:
+-----+-------------------+-----------+---------------------------------+
| | ADDRESS | VIC-II | |
|BLOCK+-------+-----------+ IMAGE | CONTENTS |
| |DECIMAL| HEX | | |
+-----+-------+-----------+-----------+---------------------------------+
| 0 | 53248 | D000-D1FF | 1000-11FF | Upper case characters |
| | 53760 | D200-D3FF | 1200-13FF | Graphics characters |
| | 54272 | D400-D5FF | 1400-15FF | Reversed upper case characters |
| | 54784 | D600-D7FF | 1600-17FF | Reversed graphics characters |
| | | | | |
| 1 | 55296 | D800-D9FF | 1800-19FF | Lower case characters |
| | 55808 | DA00-DBFF | 1A00-1BFF | Upper case & graphics characters|
| | 56320 | DC00-DDFF | 1C00-1DFF | Reversed lower case characters |
| | 56832 | DE00-DFFF | 1E00-1FFF | Reversed upper case & |
| | | | | graphics characters |
+-----+-------+-----------+-----------+---------------------------------+
Sharp-eyed readers will have just noticed something. The locations
occupied by the character ROM are the same as the ones occupied by the
VIC-II chip control registers. This is possible because they don't occupy
the same locations at the same time. When the VIC-II chip needs to access
PROGRAMMING GRAPHICS 105
~
character data the ROM is switched in. It becomes an image in the 16K
bank of memory that the VIC-II chip is looking at. Otherwise, the area is
occupied by the I/O control registers, and the character ROM is only
available to the VIC-II chip.
However, you may need to get to the character ROM if you are going to
use programmable characters and want to copy some of the character ROM
for some of your character definitions. In this case you must switch out
the I/O register, switch in the character ROM, and do your copying. When
you're finished, you must switch the 1/0 registers back in again. During
the copying process (when I/O is switched out) no interrupts can be
allowed to take place. This is because the I/O registers are needed to
service the interrupts. If you forget and perform an interrupt, really
strange things happen. The keyboard should not be read during the copying
process. To turn off the keyboard and other normal interrupts that occur
with your Commodore 64, the following POKE should be used:
POKE 56334,PEEK(56334)AND254 (TURNS INTERRUPTS OFF)
After you are finished getting characters from the character ROM, and
are ready to continue with your program, you must turn the keyboard scan
back on by the following POKE:
POKE 56334,PEEK(56334)OR1 (TURNS INTERRUPTS ON)
The following POKE will switch out 1/0 and switch the CHARACTER ROM in:
POKE 1,PEEK(1)AND251
The character ROM is now in the locations from 53248-57343 ($D000-
$DFFF).
To switch I/O back into $D000 for normal operation use the following
POKE:
POKE 1,PEEK(1)OR 4
106 PROGRAMMING GRAPHICS
~
STANDARD CHARACTER MODE
Standard character mode is the mode the Commodore 64 is in when you
first turn it on. It is the mode you will generally program in.
Characters can be taken from ROM or from RAM, but normally they are
taken from ROM. When you want special graphics characters for a program,
all you have to do is define the new character shapes in RAM, and tell
the VIC-II chip to get its character information from there instead of
the character ROM. This is covered in more detail in the next section.
In order to display characters on the screen in color, the VIC-II chip
accesses the screen memory to determine the character code for that
location on the screen. At the same time, it accesses the color memory to
determine what color you want for the character displayed. The character
code is translated by the VIC-II into the starting address of the 8-byte
block holding your character pattern. The 8-byte block is located in
character memory.
The translation isn't too complicated, but a number of items are com-
bined to generate the desired address. First the character code you use
to POKE screen memory is multiplied by 8. Next add the start of char-
acter memory (see CHARACTER MEMORY section). Then the Bank Select Bits
are taken into account by adding in the base address (see VIDEO BANK
SELECTION section). Below is a simple formula to illustrate what happens:
CHARACTER ADDRESS = SCREEN CODE*8+(CHARACTER SET*2048)+(BANK*16384)
CHARACTER DEFINITIONS
Each character is formed in an 8 by 8 grid of dots, where each dot may
be either on or off. The Commodore 64 character images are stored in the
Character Generator ROM chip. The characters are stored as a set of 8
bytes for each character, with each byte representing the dot pattern of
a row in the character, and each bit representing a dot. A zero bit means
that dot is off, and a one bit means the dot is on.
The character memory in ROM begins at location 53248 (when the I/O
is switched off). The first 8 bytes from location 53248 ($D000) to 53255
($D007) contain the pattern for the @ sign, which has a character code
value of zero in the screen memory. The next 8 bytes, from location
PROGRAMMING GRAPHICS 107
~
53256 ($D008) to 53263 ($D00F), contain the information for forming the
letter A.
IMAGE BINARY PEEK
** 00011000 24
**** 00111100 60
** ** 01100110 102
****** 01111110 126
** ** 01100110 102
** ** 01100110 102
** ** 01100110 102
00000000 0
Each complete character set takes up 2K (2048 bits) of memory, 8 bytes
per character and 256 characters. Since there are two character sets, one
for upper case and graphics and the other with upper and lower case, the
character generator ROM takes up a total of 4K locations.
PROGRAMMABLE CHARACTERS
Since the characters are stored in ROM, it would seem that there is no
way to change them for customizing characters. However, the memory
location that tells the VIC-II chip where to find the characters is a
programmable register which can be changed to point to many sections of
memory. By changing the character memory pointer to point to RAM, the
character set may be programmed for any need.
If you want your character set to be located in RAM, there are a few
VERY IMPORTANT things to take into account when you decide to actually
program your own character sets. In addition, there are two other
important points you must know to create your own special characters:
1) It is an all or nothing process. Generally, if you use your own
character set by telling the VIC-II chip to get the character
information from the area you have prepared in RAM, the standard
Commodore 64 characters are unavailable to you. To solve this, you
must copy any letters, numbers, or standard Commodore 64 graphics you
intend to use into your own character memory in RAM. You can pick and
choose, take only the ones you want, and don't even have to keep them
in order!
108 PROGRAMMING GRAPHICS
~
2) Your character set takes memory space away from your BASIC program.
Of course, with 38K available for a BASIC program, most applications
won't have problems.
+-----------------------------------------------------------------------+
| WARNING: You must be careful to protect the character set from being |
| overwritten by your BASIC program, which also uses the RAM. |
+-----------------------------------------------------------------------+
There are two locations in the Commodore 64 to start your character set
that should NOT be used with BASIC: location 0 and location 2048. The
first should not be used because the system stores important data on
page 0. The second can't be used because that is where your BASIC program
starts! However, there are 6 other starting positions for your custom
character set.
The best place to put your character set for use with BASIC while
experimenting is beginning at 12288 ($3000 in HEX). This is done by
POKEing the low 4 bits of location 53272 with 12. Try the POKE now, like
this:
POKE 53272,(PEEK(53272)AND240)+12
Immediately, all the letters on the screen turn to garbage, This is
because there are no characters set up at location 12288 right now...
only random bytes. Set the Commodore 64 back to normal by hitting the
<RUN/STOP> key and then the <RESTORE> key.
Now let's begin creating graphics characters. To protect your char-
acter set from BASIC, you should reduce the amount of memory BASIC
thinks it has. The amount of memory in your computer stays the same...
it's just that you've told BASIC not to use some of it. Type:
PRINT FRE(0)-(SGN(FRE(0))<0)*65535
The number displayed is the amount of memory space left unused. Now
type the following:
POKE 52148:POKE56,48:CLR
Now type:
PRINT FRE(0)-(SGN(FRE(0))<0)*65535
PROGRAMMING GRAPHICS 109
~
See the change? BASIC now thinks it has less memory to work with. The
memory you just claimed from BASIC is where you are going to put your
character set, safe from actions of BASIC.
The next step is to put your characters into RAM. When you begin, there
is random data beginning at 12288 ($3000 HEX). You must put character
patterns in RAM (in the same style as the ones in ROM) for the VIC-II
chip to use.
The following program moves 64 characters from ROM to your character
set RAM:
start tok64 page110.prg
5 printchr$(142) :rem switch to upper case
10 poke52,48:poke 56,48:clr :rem reserve memory for characters
20 poke56334,peek(56334)and254 :rem turn off keyscan interrupt timer
30 poke1,peek(1)and251 :rem switch in character
40 fori=0to511:pokei+12288,peek(i+53248):next
50 poke1,peek(1)or4 :rem switch in i/o
60 poke56334,peek(56334)or1 :rem restart keyscan interrupt timer
70 end
stop tok64
Now POKE location 53272 with (PEEK(53272)AND240)+12. Nothing happens,
right? Well, almost nothing. The Commodore 64 is now getting it's
character information from your RAM, instead of from ROM. But since we
copied the characters from ROM exactly, no difference can be seen... yet.
You can easily change the characters now. Clear the screen and type
an @ sign. Move the cursor down a couple of lines, then type:
FOR I=12288 TO 12288+7:POKE 1,255-PEEK(I):NEXT
You just created a reversed @ sign!
+-----------------------------------------------------------------------+
| TIP: Reversed characters are just characters with their bit patterns |
| in character memory reversed. |
+-----------------------------------------------------------------------+
Now move the cursor up to the program again and hit <RETURN> again to
re-reverse the character (bring it back to normal). By looking at the
table of screen display codes, you can figure out where in RAM each
character is. Just remember that each character takes eight memory
locations to store. Here's a few examples just to get you started:
110 PROGRAMMING GRAPHICS
~
+-----------+--------------+--------------------------------------------+
| CHARACTER | DISPLAY CODE | CURRENT STARTING LOCATION IN RAM |
+-----------+--------------+--------------------------------------------+
| @ | 0 | 1228 |
| A | 1 | 12296 |
| ! | 33 | 12552 |
| > | 62 | 12784 |
+-----------+--------------+--------------------------------------------+
Remember that we only took the first 64 characters. Something else will
have to be done if you want one of the other characters.
What if you wanted character number 154, a reversed Z? Well, you could
make it yourself, by reversing a Z, or you could copy the set of reversed
characters from the ROM, or just take the one character you want from ROM
and replace one of the characters you have in RAM that you don't need.
Suppose you decide that you won't need the > sign. Let's replace the
> sign with the reversed Z. Type this:
FOR I=0 TO 7:POKE 12784+I,255-PEEK(I+12496):NEXT
Now type a > sign. It comes up as a reversed Z. No matter how many
times you type the >, it comes out as a reversed Z. (This change is
really an illusion. Though the > sign looks like a reversed Z, it still
acts like a > in a program. Try something that needs a > sign. It will
still work fine, only it will look strange.)
A quick review: You can now copy characters from ROM into RAM. You can
even pick and choose only the ones you want. There's only one step left
in programmable characters (the best step!)... making your own
characters.
Remember how characters are stored in ROM? Each character is stored as
a group of eight bytes. The bit patterns of the bytes directly control
the character. If you arrange 8 bytes, one on top of another, and write
out each byte as eight binary digits, it forms an eight by eight matrix,
looking like the characters. When a bit is a one, there is a dot at that
location. When a bit is a zero, there is a space at that location. When
creating your own characters, you set up the same kind of table in
memory. Type NEW and then type this program:
10 FOR I=12448 TO 12455: READ A:POKE I,A:NEXT
20 DATA 60, 66, 165, 129, 165, 153, 66, 60
PROGRAMMING GRAPHICS 111
~
Now type RUN. The program will replace the letter T with a smile face
character. Type a few T's to see the face. Each of the numbers in the
DATA statement in line 20 is a row in the smile face character. The
matrix for the face looks like this:
76543210 BINARY DECIMAL
+--------+
ROW 0 | **** | 00111100 60
1 | * * | 01000010 66
2 |* * * *| 10100101 165
3 |* *| 10000001 129
4 |* * * *| 10100101 165
5 |* ** *| 10011001 153
6 | * * | 01000010 66
ROW 7 | **** | 00111100 60
+--------+
7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+
0 | | | | | | | | |
+-+-+-+-+-+-+-+-+
1 | | | | | | | | |
+-+-+-+-+-+-+-+-+
2 | | | | | | | | |
+-+-+-+-+-+-+-+-+
3 | | | | | | | | |
+-+-+-+-+-+-+-+-+
4 | | | | | | | | |
+-+-+-+-+-+-+-+-+
5 | | | | | | | | |
+-+-+-+-+-+-+-+-+
6 | | | | | | | | |
+-+-+-+-+-+-+-+-+
7 | | | | | | | | |
+-+-+-+-+-+-+-+-+
Figure 3-1. Programmable Character Worksheet.
112 PROGRAMMING GRAPHICS
~
The Programmable Character Worksheet (Figure 3-1) will help you design
your own characters. There is an 8 by 8 matrix on the sheet, with row
numbers, and numbers at the top of each column. (if you view each row as
a binary word, the numbers are the value of that bit position. Each is a
power of 2. The leftmost bit is equal to 128 or 2 to the 7th power, the
next is equal to 64 or 2 to the 6th, and so on, until you reach the
rightmost bit (bit 0) which is equal to 1 or 2 to the 0 power.)
Place an X on the matrix at every location where you want a dot to be
in your character. When your character is ready you can create the DATA
statement for your character.
Begin with the first row. Wherever you placed an X, take the number at
the top of the column (the power-of-2 number, as explained above) and
write it down. When you have the numbers for every column of the first
row, add them together. \Mite this number down, next to the row. This is
the number that you will put into the DATA statement to draw this row.
Do the same thing with all of the other rows (1-7). When you are
finished you should have 8 numbers between 0 and 255. If any of your
numbers are not within range, recheck your addition. The numbers must be
in this range to be correct! If you have less than 8 numbers, you missed
a row. It's OK if some are 0. The 0 rows are just as important as the
other numbers.
Replace the numbers in the DATA statement in line 20 with the numbers
you just calculated, and RUN the program. Then type a T. Every time you
type it, you'll see your own character!
If you don't like the way the character turned out, just change the
numbers in the DATA statement and re-RUN the program until you are happy
with your character.
That's all there is to it!
+-----------------------------------------------------------------------+
| HINT: For best results, always make any vertical lines in your |
| characters at least 2 dots (bits) wide. This helps prevent CHROMA |
| noise (color distortion) on your characters when they are displayed |
| on a TV screen. |
+-----------------------------------------------------------------------+
PROGRAMMING GRAPHICS 113
~
Here is an example of a program using standard programmable characters:
start tok64 page114.prg
10 rem * example 1 *
20 rem creating programmable characters
31 poke 56334,peek(56334)and254: rem turn off kb
32 poke 1,peek(1)and251: rem turn off i/o
35 for i=0to63: rem character range to be copied
36 for j=0to7: rem copy all 8 bytes per character
37 poke 12288+I*8+j,peek(53248+i*8+j): rem copy a byte
38 next j:next i: rem goto next byte or character
39 poke 1,peek(1)or4:poke 56334,peek(56334)or1: rem turn on i/O and kb
40 poke 53272,(peek(53272)and240)+12: rem set char pointer to mem. 12288
60 for char=60to63: rem program characters 60 thru 63
80 for byte=0to7: rem do all 8 bytes of a character
100 read number: rem read in 1/8th of character data
120 poke 12288+(8*char)+byte,number: rem store the data in memory
140 next byte:next char: rem also could be next byte, char
150 print chr$(147)tab(255)chr$(60);
155 print chr$(61)tab(55)chr$(62)chr$(63)
160 rem line 150 puts the newly defined characters on the screen
170 get a$: rem wait for user to press a key
180 if a$=""then goto170: rem if no keys were pressed, try again!
190 poke 53272,21: rem return to normal characters
200 data 4,6,7,5,7,7,3,3: rem data for character 60
210 data 32,96,224,160,224,224,192,192: rem data for character 61
220 data 7,7,7,31,31,95,143,127: rem data for character 62
230 data 224,224,224,248,248,248,240,224: rem data for character 63
240 end
stop tok64
114 PROGRAMMING GRAPHICS
~
MULTI-COLOR MODE GRAPHICS
Standard high-resolution graphics give you control of very small dots
on the screen. Each dot in character memory can have 2 possible values,
1 for on and 0 for off. When a dot is off, the color of the screen is
used in the space reserved for that dot. If the dot is on, the dot is
colored with the character color you have chosen for that screen posi-
tion. When you're using standard high-resolution graphics, all the dots
within each 8X8 character can either have background color or foreground
color. In some ways this limits the color resolution within that space.
For example, problems may occur when two different colored lines cross.
Multi-color mode gives you a solution to this problem. Each dot in
multi-color mode can be one of 4 colors: screen color (background color
register #0), the color in background register #1, the color in back-
ground color register #2, or character color. The only sacrifice is in
the horizontal resolution, because each multi-color mode dot is twice as
wide as a high-resolution dot. This minimal loss of resolution is more
than compensated for by the extra abilities of multi-color mode.
MULTI-COLOR MODE BIT
To turn on multi-color character mode, set bit 4 of the VIC-II control
register at 53270 ($D016) to a 1 by using the following POKE:
POKE 53270,PEEK(53270)OR 16
To turn off multi-color character mode, set bit 4 of location 53270 to
a 0 by the following POKE:
POKE 53270,PEEK(53270)AND 239
Multi-color mode is set on or off for each space on the screen, so that
multi-color graphics can be mixed with high-resolution (hi-res) graphics.
This is controlled by bit 3 in color memory. Color memory begins at
location 55296 ($D800 in HEX). If the number in color memory is less than
8 (0-7) the corresponding space on the video screen will be standard
hi-res, in the color (0-7) you've chosen. If the number located in color
memory is greater or equal to 8 (from 8 to 15), then that space will be
displayed in multi-color mode.
PROGRAMMING GRAPHICS 115
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By POKEing a number into color memory, you can change the color of the
character in that position on the screen. POKEing a number from 0 to 7
gives the normal character colors. POKEing a number between 8 and 15 puts
the space into multi-color mode. In other words, turning BIT 3 ON in
color memory, sets MULTI-COLOR MODE. Turning BIT 3 OFF in color memory,
sets the normal, HIGH-RESOLUTION mode.
Once multi-color mode is set in a space, the bits in the character
determine which colors are displayed for the dots. For example, here is
a picture of the letter A, and its bit pattern:
IMAGE BIT PATTERN
** 00011000
**** 00111100
** ** 01100110
****** 01111110
** ** 01100110
** ** 01100110
** ** 01100110
00000000
In normal or high-resolution mode, the screen color is displayed
everywhere there is a 0 bit, and the character color is displayed where
the bit is a 1. Multi-color mode uses the bits in pairs, like so:
IMAGE BIT PATTERN
AABB 00011000
CCCC 00111100
AABBAABB 01100110
AACCCCBB 01111110
AABBAABB 01100110
AABBAABB 01100110
AABBAABB 01100110
00000000
In the image area above, the spaces marked AA are drawn in the
background #1 color, the spaces marked BB use the background #2 color,
and the spaces marked CC use the character color. The bit pairs determine
this, according to the following chart:
116 PROGRAMMING GRAPHICS
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+----------+--------------------------------------+---------------------+
| BIT PAIR | COLOR REGISTER | LOCATION |
+----------+--------------------------------------+---------------------+
| 00 | Background #0 color (screen color) | 53281 ($D021) |
| 01 | Background #l color | 53282 ($D022) |
| 10 | Background #2 color | 53283 ($D023) |
| 11 | Color specified by the | color RAM |
| | lower 3 bits in color memory | |
+----------+--------------------------------------+---------------------+
Type NEW and then type this demonstration program:
start tok64 page117.prg
100 poke 53281,1: rem set background color #0 to white
110 poke 53282,3: rem set background color #1 to cyan
120 poke 53282,8: rem set background color #2 to orange
130 poke 53270,peek(53270)or16: rem turn on multicolor mode
140 c=13*4096+8*256: rem set c to point to color memory
150 printchr$(147)"aaaaaaaaaa"
160 forl=0to9
170 pokec+l,8: rem use multi black
180 next
stop tok64
The screen color is white, the character color is black, one color
register is cyan (greenish blue), the other is orange. You're not really
putting color codes in the space for character color, you're actually
using references to the registers associated with those colors. This
conserves memory, since 2 bits can be used to pick 16 colors (background)
or 8 colors (character). This also makes some neat tricks possible.
Simply changing one of the indirect registers will change every dot drawn
in that color. Therefore everything drawn in the screen and background
PROGRAMMING GRAPHICS 117
~
colors can be changed on the whole screen instantly. Here is an example
of changing background color register #1:
start tok64 page118.prg
100 poke53270,peek(53270)or16: rem turn on multicolor mode
110 print chr$(147)chr$(18);
120 print"{orange*2}";: rem type c= & 1 for orange or multicolor black bg
130 forl=1to22:printchr$(65);:next
135 fort=1to500:next
140 print"{blue*2}";: rem type ctrl & 7 for blue color change
145 fort=1to500:next
150 print"{black}hit a key"
160 get a$:if a$=""then160
170 x=int(rnd(1)*16)
180 poke 53282,x
190 goto 160
stop tok64
By using the <C=> key and the COLOR keys the characters can be changed
to any color, including multi-color characters. For example, type this
command:
POKE 53270,PEEK(53270)OR 16:PRINT"<CTRL+3>";: rem lt.red/ multi-color
red
The word READY and anything else you type will be displayed in multi-
color mode. Another color control can set you back to regular text.
118 PROGRAMMING GRAPHICS
~
Here is an example of a program using multi-color programmable
characters:
start tok64 page119.prg
10 rem * example 2 *
20 rem creating multi color programmable characters
31 poke 56334,peek(56334)and254:poke1,peek(1)and251
35 fori=0to63:rem character range to be copied from rom
36 forj=0to7:rem copy all 8 bytes per character
37 poke 12288+i*8+j,peek(53248+i*8+j):rem copy a byte
38 next j,i:rem goto next byte or character
39 poke 1,peek(1)or4:poke 56334,peek(56334)or1:rem turn on i/o and kb
40 poke 53272,(peek(53272)and240)+12:rem set char pointer to mem. 12288
50 poke 53270,peek(53270)or16
51 poke 53281,0:rem set background color #0 to black
52 poke 53282,2:rem set background color #1 to red
53 poke 53283,7:rem set background color #2 to yellow
60 for char=60to63:rem program characters 60 thru 63
80 for byte=0to7:rem do all 8 bytes of a character
100 read number:rem read 1/8th of the character data
120 poke 12288+(8*char)+byte,number:rem store the data in memory
140 next byte,char
150 print"{clear}"tab(255)chr$(60)chr$(61)tab(55)chr$(62)chr$(63)
160 rem line 150 puts the newly defined characters on the screen
170 get a$:rem wait for user to press a key
180 if a$=""then170:rem if no keys were pressed, try again
190 poke53272,21:poke53270,peek(53270)and239:rem return to normal chars
200 data129,37,21,29,93,85,85,85: rem data for character 60
210 data66,72,84,116,117,85,85,85: rem data for character 61
220 data87,87,85,21,8,8,40,0: rem data for character 62
230 data213,213,85,84,32,32,40,0: rem data for character 63
240 end
stop tok64
PROGRAMMING GRAPHICS 119
~
EXTENDED BACKGROUND COLOR MODE
Extended background color mode gives you control over the background
color of each individual character, as well as over the foreground color.
For example, in this mode you could display a blue character with a
yellow background on a white screen.
There are 4 registers available for extended background color mode.
Each of the registers can be set to any of the 16 colors.
Color memory is used to hold the foreground color in extended back-
ground mode. It is used the same as in standard character mode.
Extended character mode places a limit on the number of different
characters you can display, however. When extended color mode is on, only
the first 64 characters in the character ROM (or the first 64 characters
in your programmable character set) can be used. This is because two of
the bits of the character code are used to select the background color.
It might work something like this:
The character code (the number you would POKE to the screen) of the
letter "A" is a 1. When extended color mode is on, if you POKED a 1 to
the screen, an "A" would appear. If you POKED a 65 to the screen
normally, you would expect the character with character code (CHR$) 129
to appear, which is a reversed "A." This does NOT happen in extended
color mode. Instead you get the same unreversed "A" as before, but on a
different background color. The following chart gives the codes:
+------------------------+---------------------------+
| CHARACTER CODE | BACKGROUND COLOR REGISTER |
+------------------------+---------------------------+
| RANGE BIT 7 BIT 6 | NUMBER ADDRESS |
+------------------------+---------------------------+
| 0- 63 0 0 | 0 53281 ($D021) |
| 64-127 0 1 | 1 53282 ($D022) |
| 128-191 1 0 | 2 53283 ($D023) |
| 192-255 1 1 | 3 53284 ($D024) |
+------------------------+---------------------------+
Extended color mode is turned ON by setting bit 6 of the VIC-II regis-
ter to a 1 at location 53265 ($D011 in HEX). The following POKE does it:
POKE 53265,PEEK(53265)OR 64
120 PROGRAMMING GRAPHICS
~
Extended color mode is turned OFF by setting bit 6 of the VIC-II regis-
ter to a 0 at location 53265 ($D011). The following statement will do
this:
POKE 53265,PEEK(53265)AND 191
BIT MAPPED GRAPHICS
When writing games, plotting charts for business applications, or other
types of programs, sooner or later you get to the point where you want
high-resolution displays.
The Commodore 64 has been designed to do just that: high resolution is
available through bit mapping of the screen. Bit mapping is the method in
which each possible dot (pixel) of resolution on the screen is assigned
its own bit (location) in memory. If that memory bit is a one, the dot it
is assigned to is on. If the bit is set to zero, the dot is off.
High-resolution graphic design has a couple of drawbacks, which is why
it is not used all the time. First of all, it takes lots of memory to bit
map the entire screen. This is because every pixel must have a memory bit
to control it. You are going to need one bit of memory for each pixel
(or one byte for 8 pixels). Since each character is 8 by 8, and there are
40 lines with 25 characters in each line, the resolution is 320 pixels
(dots) by 200 pixels for the whole screen. That gives you 64000 separate
dots, each of which requires a bit in memory. In other words, 8000 bytes
of memory are needed to map the whole screen.
Generally, high-resolution operations are made of many short, simple,
repetitive routines. Unfortunately, this kind of thing is usually rather
slow if you are trying to write high-resolution routines in BASIC. How-
ever, short, simple, repetitive routines are exactly what machine lan-
guage does best. The solution is to either write your programs entirely
in machine language, or call machine language, high-resolution sub-
routines from your BASIC program using the SYS command from BASIC. That
way you get both the ease of writing in BASIC, and the speed of machine
language for graphics. The VSP cartridge is also available to add high-
resolution commands to COMMODORE 64 BASIC.
All of the examples given in this section will be in BASIC to make them
clear. Now to the technical details.
BIT MAPPING is one of the most popular graphics techniques in the
computer world. It is used to create highly detailed pictures. Basically,
when the Commodore 64 goes into bit map mode, it directly displays an
PROGRAMMING GRAPHICS 121
~
8K section of memory on the TV screen. When in bit map mode, you can
directly control whether an individual dot on the screen is on or off.
There are two types of bit mapping available on the Commodore 64.
They are:
1) Standard (high-resolution) bit mapped mode (320-dot by 200-dot
resolution)
2) Multi-color bit mapped mode (160-dot by 200-dot resolution)
Each is very similar to the character type it is named for: standard
has greater resolution, but fewer color selections. On the other hand,
multi-color bit mapping trades horizontal resolution for a greater number
of colors in an 8-dot by 8-dot square.
STANDARD HIGH-RESOLUTION BIT MAP MODE
Standard bit map mode gives you a 320 horizontal dot by 200 vertical
dot resolution, with a choice of 2 colors in each 8-dot by 8-dot section.
Bit map mode is selected (turned ON) by setting bit 5 of the VIC-II
control register to a 1 at location 53265 ($D011 in HEX). The following
POKE will do this:
POKE 53265,PEEK(53265)OR 32
Bit map mode is turned OFF by setting bit 5 of the VIC-II control
register to 0 at location 53265 ($D011), like this:
POKE 53265,PEEK(53265)AND 223
Before we get into the details of the bit map mode, there is one more
issue to tackle, and that is where to locate the bit map area.
HOW IT WORKS
If you remember the PROGRAMMABLE CHARACTERS section you will recall
that you were able to set the bit pattern of a character stored in RAM to
almost anything you wanted. If at the same time you change the character
that is displayed on the screen, you would be able to change a single
dot, and watch it happen. This is the basis of bit-mapping. The entire
122 PROGRAMMING GRAPHICS
~
screen is filled with programmable characters, and you make your changes
directly into the memory that the programmable characters get their
patterns from.
Each of the locations in screen memory that were used to control what
character was displayed, are now used for color information. For example,
instead of POKEing a I in location 1024 to make an "A" appear in the top
left hand corner of the screen, location 1024 now controls the colors of
the bits in that top left space.
Colors of squares in bit map mode do not come from color memory, as
they do in the character modes. Instead, colors are taken from screen
memory. The upper 4 bits of screen memory become the color of any bit
that is set to 1 in the 8 by 8 area controlled by that screen memory
location. The lower 4 bits become the color of any bit that is set to
a 0.
EXAMPLE: Type the following:
5 BASE=2*4096:POKE53272,PEEK(53272)OR8:REM PUT BIT MAP AT 8192
10 POKE53265,PEEK(53265)OR32:REM ENTER BIT MAP MODE
Now RUN the program.
Garbage appears on the screen, right? Just like the normal screen mode,
you have to clear the HIGH-RESOLUTION (HI-RES) screen before you use it.
Unfortunately, printing a CLR won't work in this case. Instead you have
to clear out the section of memory that you're using for your
programmable characters. Hit the <RUN/STOP> and <RESTORE> keys, then add
the following lines to your program to clear the HI-RES screen:
20 FORI=BASETOBASE+7999:POKEI,0:NEXT:REM CLEAR BIT
30 FORI=1024TO2023:POKEI,3:NEXT:REM SET COLOR TO CYAN AND BLACK
Now RUN the program again. You should see the screen clearing, then the
greenish blue color, cyan, should cover the whole screen. What we want to
do now is to turn the dots on and off on the HI-RES screen.
PROGRAMMING GRAPHICS 123
~
To SET a dot (turn a dot ON) or UNSET a dot (turn a dot OFF) you must
know how to find the correct bit in the character memory that you have to
set to a 1. In other words, you have to find the character you need to
change, the row of the character, and which bit of the row that you
have to change. You need a formula to calculate this.
We will use X and Y to stand for the horizontal and vertical positions
of a dot, The dot where X=0 and Y=0 is at the upper-left of the display.
Dots to the right have higher X values, and the dots toward the bottom
have higher Y values. The best way to use bit mapping is to arrange the
bit map display something like this:
0. . . . . . . . . . . . . . . . . .X. . . . . . . . . . . . . . . . .319
. .
. .
. .
. .
Y .
. .
. .
. .
. .
199. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Each dot will have an X and a Y coordinate. With this format it is easy
to control any dot on the screen.
124 PROGRAMMING GRAPHICS
~
However, what you actually have is something like this:
----- BYTE 0 BYTE 8 BYTE 16 BYTE 24 ..................... BYTE 312
BYTE 1 BYTE 9 . . BYTE 313
BYTE 2 BYTE 10 . . BYTE 314
BYTE 3 BYTE 11 . . BYTE 315
BYTE 4 BYTE 12 . . BYTE 316
BYTE 5 BYTE 13 . . BYTE 317
BYTE 6 BYTE 14 . . BYTE 318
----- BYTE 7 BYTE 15 . . BYTE 319
----- BYTE 320 BYTE 328 BYTE 336 BYTE 344....................... BYTE 632
BYTE 321 BYTE 329 . . BYTE 633
BYTE 322 BYTE 330 . . BYTE 634
BYTE 323 BYTE 331 . . BYTE 635
BYTE 324 BYTE 332 . . BYTE 636
BYTE 325 BYTE 333 . . BYTE 637
BYTE 326 BYTE 334 . . BYTE 638
----- BYTE 327 BYTE 335 . . BYTE 639
The programmable characters which make up the bit map are arranged in
25 rows of 40 columns each. While this is a good method of organization
for text, it makes bit mapping somewhat difficult. (There is a good
reason for this method. See the section on MIXED MODES.)
The following formula will make it easier to control a dot on the bit
map screen:
The start of the display memory area is known as the BASE, The row
number (from 0 to 24) of your dot is:
ROW = INT(Y/8) (There are 320 bytes per line.)
The character position on that line (from 0 to 39) is:
CHAR = INT(X/8) (There are 8 bytes per character.)
The line of that character position (from 0 to 7) is:
LINE = Y AND 7
PROGRAMMING GRAPHICS 125
~
The bit of that byte is:
BIT = 7-(X AND 7)
Now we put these formulas together. The byte in which character memory
dot (X,Y) is located is calculated by:
BYTE = BASE + ROW*320+ CHAR*8 + LINE
To turn on any bit on the grid with coordinates (X,Y), use this line:
POKE BYTE, PEEK(BYTE) OR 2^BIT
Let's add these calculations to the program. In the following example,
the COMMODORE 64 will plot a sine curve:
50 FORX=0TO319STEP.5:REM WAVE WILL FILL THE SCREEN
60 Y=INT(90+80*SIN(X/10))
70 CH=INT(X/8)
80 RO=INT(Y/8)
85 LN=YAND7
90 BY=BASE+RO*320+8*CH+LN
100 BI=7-(XAND7)
110 POKEBY,PEEK(BY)OR(2^BI)
120 NEXTX
125 POKE1024,16
130 GOTO130
The calculation in line 60 will change the values for the sine function
from a range of +1 to -1 to a range of 10 to 170. Lines 70 to 100
calculate the character, row, byte, and bit being affected, using the
formulae as shown above. Line 125 signals the program is finished by
changing the color of the top left corner of the screen. Line 130 freezes
the program by putting it into an infinite loop. When you have finished
looking at the display, just hold down <RUN/STOP> and hit <RESTORE>.
126 PROGRAMMING GRAPHICS
~
As a further example, you can modify the sine curve program to display
a semicircle. Here are the lines to type to make the changes:
50 FORX=0TO160:REM DO HALF THE SCREEN
55 Y1=100+SQR(160*X-X*X)
56 Y2=100-SQR(160*X-X*X)
60 FORY=Y1TOY2STEPY1-Y2
70 CH=INT(X/()
80 RO=INT(Y/X)
85 LNYAND7
90 BY=BASE+RO*320+8*CH+LN
100 BI=7-(XAND7)
110 POKEBY,PEEK(BY)OR(2^BI)
114 NEXT
This will create a semicircle in the HI-RES area of the screen.
+-----------------------------------------------------------------------+
| WARNING: BASIC variables can overlay your high-resolution screen. If |
| you need more memory space you must move the bottom of BASIC above the|
| high-resolution screen area. Or, you must move your high-resolution |
| screen area. This problem will NOT occur in machine language. It ONLY |
| happens when you're writing programs in BASIC. |
+-----------------------------------------------------------------------+
MULTI-COLOR BET MAP MODE
Like multi-color mode characters, multi-color bit map mode allows you
to display up to four different colors in each 8 by 8 section of bit map.
And as in multi-character mode, there is a sacrifice of horizontal
resolution (from 320 dots to 160 dots).
Multi-color bit map mode uses an 8K section of memory for the bit map.
You select your colors for multi-color bit map mode from (1) the
background color register 0, (the screen background color), (2) the video
matrix (the upper 4 bits give one possible color, the lower 4 bits an-
other), and (3) color memory.
Multi-color bit mapped mode is turned ON by setting bit 5 of 53265
($D011) and bit 4 at location 53270 ($D016) to a 1. The following POKE
does this:
POKE 53265,PEEK(53625)OR 32: POKE 53270,PEEK(53270)OR 16
PROGRAMMING GRAPHICS 127
~
Multi-color bit mapped mode is turned OFF by setting bit 5 of 53265
($D011) and bit 4 at location 53270 ($D016) to a 0. The following POKE
does this:
POKE 53265,PEEK(53265)AND 223: POKE 53270,PEEK(53270)AND 239
As in standard (HI-RES) bit mapped mode, there is a one to one cor-
respondence between the 8K section of memory being used for the display,
and what is shown on the screen. However, the horizontal dots are two
bits wide. Each 2 bits in the display memory area form a dot, which can
have one of 4 colors.
BITS COLOR INFORMATION COMES FROM
00 Background color #0 (screen color)
01 Upper 4 bits of screen memory
10 Lower 4 bits of screen memory
11 Color nybble (nybble = 1/2 byte = 4 bits)
SMOOTH SCROLLING
The VIC-II chip supports smooth scrolling in both the horizontal and
vertical directions. Smooth scrolling is a one pixel movement of the
entire screen in one direction. It can move either UP, or down, or left,
or right. It is used to move new information smoothly onto the screen,
while smoothly removing characters from the other side.
While the VIC-II chip does much of the task for you, the actual scroll-
ing must be done by a machine language program. The VIC-II chip features
the ability to place the video screen in any of 8 horizontal positions,
and 8 vertical positions. Positioning is controlled by the VIC-II
scrolling registers. The VIC-II chip also has a 38 column mode, and a 24
row mode. the smaller screen sizes are used to give you a place for your
new data to scroll on from.
The following are the steps for SMOOTH SCROLLING:
128 PROGRAMMING GRAPHICS
~
1) Shrink the screen (the border will expand).
2) Set the scrolling register to maximum (or minimum value depending upon
the direction of your scroll).
3) Place the new data on the proper (covered) portion of the screen.
4) Increment (or decrement) the scrolling register until it reaches the
maximum (or minimum) value.
5) At this point, use your machine language routine to shift the entire
screen one entire character in the direction of the scroll.
6) Go back to step 2.
To go into 38 column mode, bit 3 of location 53270 ($D016) must be set
to a 0. The following POKE does this:
POKE 53270,PEEK(53270)AND 247
To return to 40 column mode, set bit 3 of location 53270 ($D016) to a
1.The following POKE does this:
POKE 53270,PEEK(53270)OR 8
To go into 24 row mode, bit 3 of location 53265 ($D011) must be set to
a 0. The following POKE will do this:
POKE 53265,PEEK(53265)AND 247
To return to 25 row mode, set bit 3 of location 53265 ($D011) to a 1.
The following POKE does this:
POKE 53265,PEEK(53265)OR 8
When scrolling in the X direction, it is necessary to place the VIC-II
chip into 38 column mode. This gives new data a place to scroll from.
When scrolling LEFT, the new data should be placed on the right. When
scrolling RIGHT the new data should be placed on the left. Please note
that there are still 40 columns to screen memory, but only 38 are
visible.
When scrolling in the Y direction, it is necessary to place the VIC-II
chip into 24 row mode. When scrolling UP, place the new data in the LAST
row. When scrolling DOWN, place the new data on the FIRST row. Unlike X
scrolling, where there are covered areas on each side of the screen,
there is only one covered area in Y scrolling. When the Y scrolling
PROGRAMMING GRAPHICS 129
~
register is set to 0, the first line is covered, ready for new data. When
the Y scrolling register is set to 7 the last row is covered.
For scrolling in the X direction, the scroll register is located in
bits 2 to 0 of the VIC-II control register at location 53270 ($D016 in
HEX). As always, it is important to affect only those bits. The following
POKE does this:
POKE 53270,(PEEK(53270)AND 248)+X
where X is the X position of the screen from 0 to 7.
For scrolling in the Y direction, the scroll register is located in
bits 2 to 0 of the VIC-II control register at location 53265 ($D011 in
HEX). As always, it is important to affect only those bits. The following
POKE does this:
POKE 53265,(PEEK(53265)AND 248)+Y
where Y is the Y position of the screen from 0 to 7.
To scroll text onto the screen from the bottom, you would step the low-
order 3 bits of location 53265 from 0-7, put more data on the covered
line at the bottom of the screen, and then repeat the process. To scroll
characters onto the screen from left to right, you would step the low-
order 3 bits of location 53270 from 0 to 7, print or POKE another column
of new data into column 0 of the screen, then repeat the process.
If you step the scroll bits by -1, your text will move in the opposite
direction.
EXAMPLE: Text scrolling onto the bottom of the screen:
start tok64 page130.prg
10 poke53265,peek(53265)and247 :rem go into 24 row mode
20 printchr$(147) :rem clear the screen
30 forx=1to24:printchr$(17);:next :rem move the cursor to the bottom
40 poke53265,(peek(53265)and248)+7:print :rem position for 1st scroll
50 print" hello";
60 forp=6to0step-1
70 poke53265,(peek(53265)and248)+p
80 forx=1to50:next :rem delay loop
90 next:goto40
stop tok64
130 PROGRAMMING GRAPHICS
~
SPRITES
A SPRITE is a special type of user definable character which can be
displayed anywhere on the screen. Sprites are maintained directly by the
VIC-II chip. And all you have to do is tell a sprite "what to look like,"
"what color to be," and "where to appear." The VIC-II chip will do the
rest! Sprites can be any of the 16 colors available.
Sprites can be used with ANY of the other graphics modes, bit mapped,
character, multi-color, etc., and they'll keep their shape in all of
them. The sprite carries its own color definition, its own mode (HI-RES
or multi-colored), and its own shape.
Up to 8 sprites at a time can be maintained by the VIC-II chip auto-
matically. More sprites can be displayed using RASTER INTERRUPT
techniques.
The features of SPRITES include:
1) 24 horizontal dot by 21 vertical dot size.
2) Individual color control for each sprite.
3) Sprite multi-color mode.
4) Magnification (2x) in horizontal, vertical, or both directions.
5) Selectable sprite to background priority.
6) Fixed sprite to sprite priorities.
7) Sprite to sprite collision detection.
8) Sprite to background collision detection.
These special sprite abilities make it simple to program many arcade
style games. Because the sprites are maintained by hardware, it is even
possible to write a good quality game in BASIC!
There are 8 sprites supported directly by the VIC-II chip. They are
numbered from 0 to 7. Each of the sprites has it own definition location,
position registers and color register, and has its own bits for enable
and collision detection.
DEFINING A SPRITE
Sprites are defined like programmable characters are defined. However,
since the size of the sprite is larger, more bytes are needed. A sprite
is 24 by 21 dots, or 504 dots. This works out to 63 bytes (504/8 bits)
PROGRAMMING GRAPHICS 131
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[THE PICTURE IS MISSING!]
Figure 3-2. Sprite Definition Block.
132 PROGRAMMING GRAPHICS
~
needed to define a sprite. The 63 bytes are arranged in 21 rows of 3
bytes each. A sprite definition looks like this.
BYTE 0 BYTE 1 BYTE 2
BYTE 3 BYTE 4 BYTE 5
BYTE 6 BYTE 7 BYTE 8
.. .. ..
.. .. ..
.. .. ..
BYTE 60 BYTE 61 BYTE 62
Another way to view how a sprite is created is to take a look at the
sprite definition block on the bit level. It would look something like
Figure 3-2.
In a standard (HI-RES) sprite, each bit set to I is displayed in that
sprite's foreground color. Each bit set to 0 is transparent and will
display whatever data is behind it. This is similar to a standard
character.
Multi-color sprites are similar to multi-color characters. Horizontal
resolution is traded for extra color resolution. The resolution of the
sprite becomes 12 horizontal dots by 21 vertical dots. Each dot in the
sprite becomes twice as wide, but the number of colors displayable in the
sprite is increased to 4.
SPRITE POINTERS
Even though each sprite takes only 63 bytes to define, one more byte
is needed as a place holder at the end of each sprite. Each sprite, then,
takes up 64 bytes. This makes it easy to calculate where in memory your
sprite definition is, since 64 bytes is an even number and in binary it's
an even power.
Each of the 8 sprites has a byte associated with it called the SPRITE
POINTER. The sprite pointers control where each sprite definition is lo-
cated in memory. These 8 bytes are always located as the lost 8 bytes
of the 1K chunk of screen memory. Normally, on the Commodore 64, this
means they begin at location 2040 ($07F8 in HEX). However, if you move
the screen, the location of your sprite pointers will also move.
Each sprite pointer can hold a number from 0 to 255. This number points
to the definition for that sprite. Since each sprite definition takes
64 bytes, that means that the pointer can "see" anywhere in the 16K
block of memory that the VIC-II chip can access (since 256*64=16K).
PROGRAMMING GRAPHICS 133
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If sprite pointer #0, at location 2040, contains the number 14, for
example, this means that sprite 0 will be displayed using the 64 bytes
beginning at location 14*64 = 896 which is in the cassette buffer. The
following formula makes this clear:
LOCATION = (BANK * 16384) + (SPRITE POINTER VALUE * 64)
Where BANK is the 16K segment of memory that the VIC-II chip is looking
at and is from 0 to 3.
The above formula gives the start of the 64 bytes of the sprite
definition block.
When the VIC-II chip is looking at BANK 0 or BANK 2, there is a ROM
IMAGE of the character set present in certain locations, as mentioned
before. Sprite definitions can NOT be placed there. If for some reason
you need more than 128 different sprite definitions, you should use one
of the banks without the ROM IMAGE, 1 or 3.
TURNING SPRITES ON
The VIC-II control register at location 53269 ($D015 in HEX) is known
as the SPRITE ENABLE register. Each of the sprites has a bit in this
register which controls whether that sprite is ON or OFF. The register
looks like this:
$D015 7 6 5 4 3 2 1 0
To turn on sprite 1, for example, it is necessary to turn that bit to
a 1. The following POKE does this:
POKE 53269.PEEK(53269)OR 2
A more general statement would be the following:
POKE 53269,PEEK(53269)OR (2^SN)
where SN is the sprite number, from 0 to 7.
+-----------------------------------------------------------------------+
| NOTE: A sprite must be turned ON before it can be seen. |
+-----------------------------------------------------------------------+
134 PROGRAMMING GRAPHICS
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TURNING SPRITES OFF
A sprite is turned off by setting its bit in the VIC-II control
register at 53269 ($D015 in HEX) to a 0. The following POKE will do this:
POKE 53269,PEEK(53269)AND(255-2^SN)
where SN is the sprite number from 0 to 7.
COLORS
A sprite can be any of the 16 colors generated by the VIC-II chip. Each
of the sprites has its own sprite color register. These are the memory
locations of the color registers:
ADDRESS | DESCRIPTION
--------------------------+----------------------------------------------
53287 ($D027) | SPRITE 0 COLOR REGISTER
53288 ($D028) | SPRITE 1 COLOR REGISTER
53289 ($D029) | SPRITE 2 COLOR REGISTER
53290 ($D02A) | SPRITE 3 COLOR REGISTER
53291 ($D02B) | SPRITE 4 COLOR REGISTER
53292 ($D02C) | SPRITE 5 COLOR REGISTER
53293 ($D02D) | SPRITE 6 COLOR REGISTER
53294 ($D02E) | SPRITE 7 COLOR REGISTER
All dots in the sprite will be displayed in the color contained in the
sprite color register. The rest of the sprite will be transparent, and
will show whatever is behind the sprite.
MULTI-COLOR MODE
Multi-color mode allows you to have up to 4 different colors in each
sprite. However, just like other multi-color modes, horizontal resolution
is cut in half. In other words, when you're working with sprite multi-
color mode (like in multi-color character mode), instead of 24 dots
across the sprite, there are 12 pairs of dots. Each pair of dots is
called a BIT PAIR. Think of each bit pair (pair of dots) as a single dot
in your overall sprite when it comes to choosing colors for the dots in
your sprites. The table below gives you the bit pair values needed to
PROGRAMMING GRAPHICS 135
~
turn ON each of the four colors you've chosen for your sprite:
BIT PAIR DESCRIPTION
-------------------------------------------------------------------------
00 TRANSPARENT, SCREEN COLOR
01 SPRITE MULTI-COLOR REGISTER #0 (53285) ($D025)
10 SPRITE COLOR REGISTER
11 SPRITE MULTI-COLOR REGISTER #I (53286) ($D026)
+-----------------------------------------------------------------------+
| NOTE: The sprite foreground color is a 10. The character foreground |
| is a 11. |
+-----------------------------------------------------------------------+
SETTING A SPRITE TO MULTI-COLOR MODE
To switch a sprite into multi-color mode you must turn ON the VIC-II
control register at location 53276 ($D01C). The following POKE does this:
POKE 53276,PEEK(53276)OR(2^SN)
where SN is the sprite number (0 to 7).
To switch a sprite out of multi-color mode you must turn OFF the VIC-II
control register at location 53276 ($D01C). The following POKE does this:
POKE 53276,PEEK(53276)AND(255-2^SN)
where SN is the sprite number (0 to 7).
EXPANDED SPRITES
The VIC-II chip has the ability to expand a sprite in the vertical
direction, the horizontal direction, or both at once. When expanded, each
dot in the sprite is twice as wide or twice as tall. Resolution doesn't
actually increase... the sprite just gets bigger.
To expand a sprite in the horizontal direction, the corresponding bit
in the VIC-II control register at location 53277 ($D01D in HEX) must be
turned ON (set to a 1). The following POKE expands a sprite in the X
direction:
POKE 53277,PEEK(53277)OR(2^SN)
where SN is the sprite number from 0 to 7.
136 PROGRAMMING GRAPHICS
~
To unexpand a sprite in the horizontal direction, the corresponding bit
in the VIC-II control register at location 53277 ($D01D in HEX) must be
turned OFF (set to a 0). The following POKE "unexpands" a sprite in the
X direction:
POKE 53277,PEEK(53277)AND (255-2^SN)
where SN is the sprite number from 0 to 7.
To expand a sprite in the vertical direction, the corresponding bit in
the VIC-II control register at location 53271 ($D017 in HEX) must be
turned ON (set to a 1). The following POKE expands a sprite in the Y
direction:
POKE 53271,PEEK(53271)OR(2^SN)
where SN is the sprite number from 0 to 7.
To unexpand a sprite in the vertical direction, the corresponding bit
in the VIC-II control register at location 53271 ($D017 in HEX) must be
turned OFF (set to a 0). The following POKE "unexpands" a sprite in the
Y direction:
POKE 53271,PEEK(53271)AND (255-2^SN)
where SN is the sprite number from 0 to 7.
SPRITE POSITIONING
Once you've made a sprite you want to be able to move it around the
screen. To do this, your Commodore 64 uses three positioning registers:
1) SPRITE X POSITION REGISTER
2) SPRITE Y POSITION REGISTER
3) MOST SIGNIFICANT BIT X POSITION REGISTER
Each sprite has an X position register, a Y position register, and a
bit in the X most significant bit register. This lets you position your
sprites very accurately. You can place your sprite in 512 possible X
positions and 256 possible Y positions.
The X and Y position registers work together, in pairs, as a team. The
locations of the X and Y registers appear in the memory map as follows:
First is the X register for sprite 0, then the Y register for sprite 0.
PROGRAMMING GRAPHICS 137
~
Next comes the X register for sprite 1, the Y register for sprite 1, and
so on. After all 16 X and Y registers comes the most significant bit in
the X position (X MSB) located in its own register.
The chart below lists the locations of each sprite position register.
You use the locations at their appropriate time through POKE statements:
+-------------------+---------------------------------------------------+
| LOCATION | |
+---------+---------+ DESCRIPTION |
| DECIMAL | HEX | |
+---------+---------+---------------------------------------------------+
| 53248 | ($D000) | SPRITE 0 X POSITION REGISTER |
| 53249 | ($D001) | SPRITE 0 Y POSITION REGISTER |
| 53250 | ($D002) | SPRITE 1 X POSITION REGISTER |
| 53251 | ($D003) | SPRITE 1 Y POSITION REGISTER |
| 53252 | ($D004) | SPRITE 2 X POSITION REGISTER |
| 53253 | ($D005) | SPRITE 2 Y POSITION REGISTER |
| 53254 | ($D006) | SPRITE 3 X POSITION REGISTER |
| 53255 | ($D007) | SPRITE 3 Y POSITION REGISTER |
| 53256 | ($D008) | SPRITE 4 X POSITION REGISTER |
| 53257 | ($D009) | SPRITE 4 Y POSITION REGISTER |
| 53258 | ($D00A) | SPRITE 5 X POSITION REGISTER |
| 53259 | ($D00B) | SPRITE 5 Y POSITION REGISTER |
| 53260 | ($D00C) | SPRITE 6 X POSITION REGISTER |
| 53261 | ($D00D) | SPRITE 6 Y POSITION REGISTER |
| 53262 | ($D00E) | SPRITE 7 X POSITION REGISTER |
| 53263 | ($D00F) | SPRITE 7 Y POSITION REGISTER |
| 53264 | ($D010) | SPRITE X MSB REGISTER |
+---------+---------+---------------------------------------------------+
The position of a sprite is calculated from the TOP LEFT corner of the
24 dot by 21 dot area that your sprite can be designed in. It does NOT
matter how many or how few dots you use to make up a sprite. Even if only
one dot is used as a sprite, and you happen to want it in the middle of
the screen, you must still calculate the exact positioning by starting at
the top left corner location.
VERTICAL POSITIONING
Setting up positions in the horizontal direction is a little more
difficult than vertical positioning, so we'll discuss vertical (Y)
positioning first.
138 PROGRAMMING GRAPHICS
~
There are 200 different dot positions that can be individually pro-
grammed onto your TV screen in the Y direction. The sprite Y position
registers can handle numbers up to 255. This means that you have more
than enough register locations to handle moving a sprite up and down. You
also want to be able to smoothly move a sprite on and off the screen.
More than 200 values are needed for this.
The first on-screen value from the top of the screen, and in the Y
direction for an unexpanded sprite is 30. For a sprite expanded in the Y
direction it would be 9. (Since each dot is twice as tall, this makes a
certain amount of sense, as the initial position is STILL calculated from
the top left corner of the sprite.)
The first Y value in which a sprite (expanded or not) is fully on the
screen (all 21 possible lines displayed) is 50.
The last Y value in which an unexpanded sprite is fully on the screen
is 229. The last Y value in which an expanded sprite is fully on the
screen is 208.
The first Y value in which a sprite is fully off the screen is 250.
EXAMPLE:
start tok64 page139.prg
10 print"{clear}" :rem clear screen
20 poke 2040,13 :rem get sprite 0 data from block 13
30 fori=0to62:poke832+i,129:next :rem poke sprite data into block 13
40 v=53248 :rem set beginning of video chip
50 pokev+21,1 :rem enable sprite 0
60 pokev+39,1 :rem set sprite 0 color
70 pokev+1,100 :rem set sprite 0 y position
80 pokev+16,0:pokev,100 :rem set sprite 0 x position
stop tok64
HORIZONTAL POSITIONING
Positioning in the horizontal direction is more complicated because
there are more than, 256 positions. This means that an extra bit, or 9th
bit is used to control the X position. By adding the extra bit when
necessary a sprite now has 512 possible positions in the left/right, X,
direction. This makes more possible combinations than can be seen on the
visible part of the screen. Each sprite can have a position from 0 to
511. However, only those values between 24 and 343 are visible on the
screen. If the X position of a sprite is greater than 255 (on the right
side of the screen), the bit in the X MOST SIGNIFICANT BIT POSITION
PROGRAMMING GRAPHICS 139
~
0 ($00) 24 ($18) 296 ($128) 344 ($158)
| |
| |
| | +----+ 8 ($08)
| | |
29 ($1D) | +--+ | |
| | | | |
| | | |
50 ($32) +--+-------------------------------------+----+----+ 50 ($32)
| | | | | |
| | | | | |
+--+--+ | | |
| | | |
| +----+----+
| |
| VISIBLE VIEWING AREA |
| |
| |
| |
| |
| |
| |
| |
| NTSC* |
| 40 COLUMNS |
| 25 ROWS |
208 ($D0) +----+----+ |
| | | |
| | | +--+--+ 299 ($E5)
| | | | | |
| | | | | |
250 ($FA) +----+----+----------------------------------+--+--+ 250 ($FA)
| | | |
| | | | |
| | | +--+
| | |
+----+ | |
488 ($1E8)
| 320 ($140) 344 ($158)
24 ($18)
*North American television transmission standards for your home TV.
140 PROGRAMMING GRAPHICS
~
7 ($07) 31 ($1F) 287 ($11F) 335 ($14F)
| |
| |
| | +----+ 12 ($0C)
| | |
33 ($21) | +--+ | |
| | | | |
| | | |
54 ($36) +--+-------------------------------------+----+----+ 54 ($36)
| | | | | |
| | | | | |
+--+--+ | | |
| | | |
| +----+----+
| |
| VISIBLE VIEWING AREA |
| |
| |
| |
| |
| |
| |
| |
| NTSC* |
| 38 COLUMNS |
| 24 ROWS |
204 ($CC) +----+----+ |
| | | |
| | | +--+--+ 225 ($E1)
| | | | | |
| | | | | |
246 ($F6) +----+----+----------------------------------+--+--+ 246 ($F6)
| | | |
| | | | |
| | | +--+
| | |
+----+ | |
480 ($1E0)
| 311 ($137) 335 ($14F)
31 ($1F)
*North American television transmission standards for your home TV.
PROGRAMMING GRAPHICS 141
~
register must be set to a 1 (turned ON). If the X position of a sprite is
less than 256 (on the left side of the screen), then the X MSB of that
sprite must be 0 (turned OFF). Bits 0 to 7 of the X MSB register
correspond to sprites 0 to 7, respectively.
The following program moves a sprite across the screen:
EXAMPLE:
start tok64 p142_1.prg
10 print"{clear}"
20 poke2040,13
30 fori=0to62:poke832+i,129:next
40 v=53248
50 pokev+21,1
60 pokev+39,1
70 pokev+1,100
80 forj=0to347
90 hx=int(j/256):lx=j-256*hx
100 pokev,lx:pokev+16,hx:next
stop tok64
When moving expanded sprites onto the left side of the screen in the
X direction, you have to start the sprite OFF SCREEN on the RIGHT SIDE.
This is because an expanded sprite is larger than the amount of space
available on the left side of the screen.
EXAMPLE:
start tok64 p142_2.prg
10 print"{clear}"
20 poke2040,13
30 fori=0to62:poke832+i,129:next
40 v=53248
50 pokev+21,1
60 pokev+39,1:pokev+23,1:pokev+29,1
70 pokev+1,100
80 j=488
90 hx=int(j/256):lx=j-256*hx
100 pokev,lx:pokev+16,hx
110 j=j+1:ifj>511thenj=0
120 ifj>488orj<348goto90
stop tok64
142 PROGRAMMING GRAPHICS
~
The charts in Figure 3-3 explain sprite positioning.
By using these values, you can position each sprite anywhere. By moving
the sprite a single dot position at a time, very smooth movement is easy
to achieve.
SPRITE POSITIONING SUMMARY
Unexpanded sprites are at least partially visible in the 40 column, by
25 row mode within the following parameters:
1 < X < 343
30 < Y < 249
In the 38 column mode, the X parameters change to she following:
8 <= X <= 334
In the 24 row mode, the Y parameters change to the following:
34 <= Y <= 245
Expanded sprites are at least partially visible in the 40 column, by 25
row mode within the following parameters:
489 >= X <= 343
9 >= Y <= 249
In the 38 column mode, the X parameters change to the following:
496 >= X <= 334
In the 24 row mode, the Y parameters change to the following:
13 <= Y <= 245
PROGRAMMING GRAPHICS 143
~
SPRITE DISPLAY PRIORITIES
Sprites have the ability to cross each other's paths, as well as cross
in front of, or behind other objects on the screen. This can give you a
truly three dimensional effect for games.
Sprite to sprite priority is fixed. That means that sprite 0 has the
highest priority, sprite 1 has the next priority, and so on, until we get
to sprite 7, which has the lowest priority. In other words, if sprite 1
and sprite 6 are positioned so that they cross each other, sprite 1 will
be in front of sprite 6.
So when you're planning which sprites will appear to be in the fore-
ground of the picture, they must be assigned lower sprite numbers than
those sprites you want to put towards the back of the scene. Those
sprites will be given higher sprite numbers,
+-----------------------------------------------------------------------+
| NOTE: A "window" effect is possible. If a sprite with higher priority |
| has "holes" in it (areas where the dots are not set to 1 and thus |
| turned ON), the sprite with the lower priority will show through. This|
| also happens with sprite and background data. |
+-----------------------------------------------------------------------+
Sprite to background priority is controllable by the SPRITE-BACK-
GROUND priority register located at 53275 ($D01B). Each sprite has a bit
in this register. If that bit is 0, that sprite has a higher priority
than the background on the screen. In other words, the sprite appears in
front of background data. If that bit is a 1, that sprite has a lower
priority than the background. Then the sprite appears behind the back-
ground data.
COLLISION DETECTS
One of the more interesting aspects of the VIC-II chip is its collision
detection abilities. Collisions can be detected between sprites, or be-
tween sprites and background data. A collision occurs when a non-zero
part of a sprite overlaps a non-zero portion of another sprite or char-
acters on the screen.
144 PROGRAMMING GRAPHICS
~
SPRITE TO SPRITE COLLISIONS
Sprite to sprite collisions are recognized by the computer, or flagged,
in the sprite to sprite collision register at location 53278 ($D01E in
HEX) in the VIC-II chip control register. Each sprite has a bit in this
register. If that bit is a 1, then that sprite is involved in a
collision. The bits in this register will remain set until read (PEEKed).
Once read, the register is automatically cleared, so it is a good idea to
save the value in a variable until you are finished with it.
+-----------------------------------------------------------------------+
| NOTE: Collisions can take place even when the sprites are off screen. |
+-----------------------------------------------------------------------+
SPRITE TO DATA COLLISIONS
Sprite to data collisions are detected in the sprite to data collision
register at location 53279 ($D01F in HEX) of the VIC-II chip control
register.
Each sprite has a bit in this register. If that bit is a 1 , then that
sprite is involved in a collision. The bits in this register remain set
until read (PEEKed). Once read, the register is automatically cleared, so
it is a good idea to save the value in a variable until you are finished
with it.
+-----------------------------------------------------------------------+
| NOTE: MULTI-COLOR data 01 is considered transparent for collisions, |
| even though it shows up on the screen. When setting up a background |
| screen, it is a good idea to make everything that should not cause a |
| collision 01 in multi-color mode. |
+-----------------------------------------------------------------------+
PROGRAMMING GRAPHICS 145
~
start tok64 page146.prg
10 rem sprite example 1... the hot air balloon
30 vic=13*4096:rem this is where the vic registers begin
35 pokevic+21,1:rem enable sprite 0
36 pokevic+33,14:rem set background color to light blue
37 pokevic+23,1:rem expand sprite 0 in y
38 pokevic+29,1:rem expand sprite 0 in x
40 poke2040,192:rem set sprite 0's pointer
180 pokevic+0,100:rem set sprite 0's x position
190 pokevic+1,100:rem set sprite 0's y position
220 pokevic+39,1:rem set sprite 0's color
250 fory=0to63:rem byte counter with sprite loop
300 reada:rem read in a byte
310 poke192*64+y,a:rem store the data in sprite area
320 nexty:rem close loop
330 dx=1:dy=1
340 x=peek(vic):rem look at sprite 0's x position
350 y=peek(vic+1):rem look at sprite 0's y position
360 ify=50ory=208thendy=-dy:rem if y is on the edge of the...
370 rem screen, then reverse delta y
380 ifx=24and(peek(vic+16)and1)=0thendx=-dx:rem if sprite is touching...
390 rem the left edge(x=24 and the msb for sprite 0 is 0), reverse it
400 ifx=40and(peek(vic+16)and1)=1thendx=-dx:rem if sprite is touching...
410 rem the right edge (x=40 and the msb for sprite 0 is 1), reverse it
420 ifx=255anddx=1thenx=-1:side=1
430 rem switch to other side of the screen
440 ifx=0anddx=-1thenx=256:side=0
450 rem switch to other side of the screen
460 x=x+dx:rem add delta x to x
470 x=xand255:rem make sure x is in allowed range
480 y=y+dy:rem add delta y to y
485 pokevic+16,side
490 pokevic,x:rem put new x value into sprite 0's x position
510 pokevic+1,y:rem put new y value into sprite 0's y position
530 goto340
600 rem ***** sprite data *****
610 data0,127,0,1,255,192,3,255,224,3,231,224
620 data7,217,240,7,223,240,7,217,240,3,231,224
630 data3,255,224,3,255,224,2,255,160,1,127,64
640 data1,62,64,0,156,128,0,156,128,0,73,0,0,73,0
650 data0,62,0,0,62,0,0,62,0,0,28,0,0
stop tok64
146 PROGRAMMING GRAPHICS
~
start tok64 page147.prg
10 rem sprite example 2...
20 rem the hot air balloon again
30 vic=13*4096:rem this is where the vic registers begin
35 pokevic+21,63:rem enable sprites 0 thru 5
36 pokevic+33,14:rem set background color to light blue
37 pokevic+23,3:rem expand sprites 0 and 1 in y
38 pokevic+29,3:rem expand sprites 0 and 1 in x
40 poke2040,192:rem set sprite 0's pointer
50 poke2041,193:rem set sprite 1's pointer
60 poke2042,192:rem set sprite 2's pointer
70 poke2043,193:rem set sprite 3's pointer
80 poke2044,192:rem set sprite 4's pointer
90 poke2045,193:rem set sprite 5's pointer
100 pokevic+4,30:rem set sprite 2's x position
110 pokevic+5,58:rem set sprite 2's y position
120 pokevic+6,65:rem set sprite 3's x position
130 pokevic+7,58:rem set sprite 3's y position
140 pokevic+8,100:rem set sprite 4's x position
150 pokevic+9,58:rem set sprite 4's y position
160 pokevic+10,100:rem set sprite 5's x position
170 pokevic+11,58:rem set sprite 5's y position
175 print"{white}{clear}"tab(15)"this is two hires sprites";
176 printtab(55)"on top of each other"
180 pokevic+0,100:rem set sprite 0's x position
190 pokevic+1,100:rem set sprite 0's y position
200 pokevic+2,100:rem set sprite 1's x position
210 pokevic+3,100:rem set sprite 1's y position
220 pokevic+39,1:rem set sprite 0's color
230 pokevic+41,1:rem set sprite 2's color
240 pokevic+43,1:rem set sprite 4's color
250 pokevic+40,6:rem set sprite 1's color
260 pokevic+42,6:rem set sprite 3's color
270 pokevic+44,6:rem set sprite 5's color
280 forx=192to193:rem the start of the loop that defines the sprites
290 fory=0to63:rem byte counter with sprite loop
300 reada:rem read in a byte
310 pokex*64+y,a:rem store the data in sprite area
320 nexty,x:rem close loops
330 dx=1:dy=1
340 x=peek(vic):rem look at sprite 0's x position
350 ify=50ory=208thendy=-dy:rem if y is on the edge of the...
370 rem screen, then reverse delta y
380 ifx=24and(peek(vic+16)and1)=0thendx=-dx:rem if sprite is...
390 rem touching the left edge, then reverse it
400 ifx=40and(peek(vic+16)and1)=1thendx=-dx:rem if sprite is...
410 rem touching the right edge, then reverse it
420 ifx=255anddx=1thenx=-1:side=3
430 rem switch to other side of the screen
440 ifx=0anddx=-1thenx=256:side=0
450 rem switch to other side of the screen
460 x=x+dx:rem add delta x to x
470 x=xand255:rem make sure x is in allowed range
480 y=y+dy:rem add delta y to y
485 pokevic+16,side
490 pokevic,x:rem put new x value into sprite 0's x position
500 pokevic+2,x:rem put new x value into sprite 1's x position
510 pokevic+1,y:rem put new y value into sprite 0's y position
520 pokevic+3,y:rem put new y value into sprite 1's y position
530 goto340
600 rem ***** sprite data *****
610 data0,255,0,3,153,192,7,24,224,7,56,224,14,126,112,14,126,112,14,126
620 data112,6,126,96,7,56,224,7,56,224,1,56,128,0,153,0,0,90,0,0,56,0
630 data0,56,0,0,0,0,0,0,0,0,126,0,0,42,0,0,84,0,0,40,0,0
640 data0,0,0,0,102,0,0,231,0,0,195,0,1,129,128,1,129,128,1,129,128
650 data1,129,128,0,195,0,0,195,0,4,195,32,2,102,64,2,36,64,1,0,128
660 data1,0,128,0,153,0,0,153,0,0,0,0,0,84,0,0,42,0,0,20,0,0
stop tok64
start tok64 page148.prg
10 rem sprite example 3...
20 rem the hot air gorf
30 vic=53248:rem this is where the vic registers begin
35 pokevic+21,1:rem enable sprite 0
36 pokevic+33,14:rem set background color to light blue
37 pokevic+23,1:rem expand sprite 0 in y
38 pokevic+29,1:rem expand sprite 0 in x
40 poke2040,192:rem set sprite 0's pointer
50 pokevic+28,1:rem turn on multicolor
60 pokevic+37,7:rem set multicolor 0
70 pokevic+38,4:rem set multicolor 1
180 pokevic+0,100:rem set sprite 0's x position
190 pokevic+1,100:rem set sprite 0's y position
220 pokevic+39,2:rem set sprite 0's color
290 fory=0to63:rem byte counter with sprite loop
300 reada:rem read in a byte
310 poke12288+y,a:rem store the data in sprite area
320 next y:rem close loop
330 dx=1:dy=1
340 x=peek(vic):rem look at sprite 0's x position
350 y=peek(vic+1):rem look at sprite 0's y position
360 ify=50ory=208then dy=-dy:rem if y is on the edge of the...
370 rem screen, then reverse delta y
380 ifx=24and(peek(vic+16)and1)=0thendx=-dx:rem if sprite is...
390 rem touching the left edge, then reverse it
400 ifx=40and(peek(vic+16)and1)=1thendx=-dx:rem if sprite is...
410 rem touching the right edge, then reverse it
420 ifx=255anddx=1thenx=-1:side=1
430 rem switch to other side of the screen
440 ifx=0anddx=-1thenx=256:side=0
450 rem switch to other side of the screen
460 x=x+dx:rem add delta x to x
470 x=xand255:rem make sure that x is in allowed range
480 y=y+dy:rem add delta y to y
485 pokevic+16,side
490 pokevic,x:rem put new x value into sprite 0's x position
510 pokevic+1,y:rem put new y value into sprite 0's y position
520 geta$:rem get a key from the keyboard
521 ifa$="m"thenpokevic+28,1:rem user selected multicolor
522 ifa$="h"thenpokevic+28,0:rem user selected high resolution
530 goto340
600 rem ***** sprite data *****
610 data64,0,1,16,170,4,6,170,144,10,170,160,42,170,168,41,105,104,169
620 data235,106,169,235,106,169,235,106,170,170,170,170,170,170,170,170
630 data170,170,170,170,166,170,154,169,85,106,170,85,170,42,170,168,10
640 data170,160,1,0,64,1,0,64,5,0,80,0
stop tok64
PROGRAMMING GRAPHICS 149
~
OTHER GRAPHICS FEATURES
SCREEN BLANKING
Bit 4 of the VIC-II control register controls the screen blanking func-
tion. It is found in the control register at location 53265 ($D011). When
it is turned ON (in other words, set to a 1) the screen is normal. When
bit 4 is set to 0 (turned OFF), the entire screen changes to border
color.
The following POKE blanks the screen. No data is lost, it just isn't
displayed.
POKE 53265,PEEK(53265)AND 239
To bring back the screen. use the POKE shown below:
POKE 53265,PEEK(53265)OR 16
+-----------------------------------------------------------------------+
| NOTE: Turning off the screen will speed up the processor slightly. |
| This means that program RUNning is also sped up. |
+-----------------------------------------------------------------------+
RASTER REGISTER
The raster register is found in the VIC-II chip at location 53266
($D012). The raster register is a dual purpose register. When you read
this register it returns the lower 8 bits of the current raster position.
The raster position of the most significant bit is in register location
53265 ($D011). You use the raster register to set up timing changes in
your display so that you can get rid of screen flicker. The changes on
your screen should be mode when the raster is not in the visible display
area, which is when your dot positions fall between 51 and 251.
When the raster register is written to (including the MSB) the number
written to is saved for use with the raster compare function. When the
actual raster value becomes the same as the number written to the raster
register, a bit in the VIC-II chip interrupt register 53273 ($D019) is
turned ON by setting it to 1.
+-----------------------------------------------------------------------+
| NOTE: If the proper interrupt bit is enabled (turned on), an interrupt|
| (IRQ) will occur. |
+-----------------------------------------------------------------------+
150 PROGRAMMING GRAPHICS
~
INTERRUPT STATUS REGISTER
The interrupt status register shows the current status of any interrupt
source. The current status of bit 2 of the interrupt register will be a 1
when two sprites hit each other. The same is true, in a corresponding 1
to 1 relationship, for bits 0-3 listed in the chart below. Bit 7 is also
set with a 1, whenever an interrupt occurs.
The interrupt status register is located at 53273 ($D019) and is as
follows:
LATCH BIT# DESCRIPTION
-------------------------------------------------------------------------
IRST 0 Set when current raster count = stored raster count
IMDC 1 Set by SPRITE-DATA collision (1st one only, until reset)
IMMC 2 Set by SPRITE-SPRITE collision (1st one only, until reset)
ILP 3 Set by negative transition of light pen (1 per frame)
IRQ 7 Set by latch set and enabled
-------------------------------------------------------------------------
Once an interrupt bit has been set, it's "latched" in and must be
cleared by writing a 1 to that bit in the interrupt register when you're
ready to handle it. This allows selective interrupt handling, without
having to store the other interrupt bits.
The INTERRUPT ENABLE REGISTER is located at 53274 ($D01A). It has the
same format as the interrupt status register. Unless the corresponding
bit in the interrupt enable register is set to a 1, no interrupt from
that source will take place. The interrupt status register can still be
polled for information, but no interrupts will be generated.
To enable an interrupt request the corresponding interrupt enable bit
(as shown in the chart above) must be set to a 1.
This powerful interrupt structure lets you use split screen modes. For
instance you can have half of the screen bit mapped, half text, more than
8 sprites at a time, etc. The secret is to use interrupts properly. For
example, if you want the top half of the screen to be bit mapped and the
bottom to be text, just set the raster compare register (as explained
previously) for halfway down the screen. When the interrupt occurs, tell
the VIC-II chip to get characters from ROM, then set the raster compare
register to interrupt at the top of the screen. When the interrupt occurs
at the top of the screen, tell the VIC-II chip to get characters from RAM
(bit map mode).
You can also display more than 8 sprites in the same way. Unfortunately
BASIC isn't fast enough to do this very well. So if you want to start
using display interrupts, you should work in machine language.
PROGRAMMING GRAPHICS 151
~
SUGGESTED SCREEN AND CHARACTER COLOR COMBINATIONS
Color TV sets are limited in their ability to place certain colors next
to each other on the same line. Certain combinations of screen and char-
acter colors produce blurred images. This chart shows which color com-
binations to avoid, and which work especially well together.
CHARACTER COLOR
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
0| x| o| x| o| o| /| x| o| o| x| o| o| o| o| o| o|
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
1| o| x| o| x| o| o| o| x| /| o| /| o| o| x| o| o|
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
2| x| o| x| x| /| x| x| o| o| x| o| x| x| x| x| /|
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
3| o| x| x| x| x| /| o| x| x| x| x| /| x| x| /| x|
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
4| o| /| x| x| x| x| x| x| x| x| x| x| x| x| x| /|
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
5| o| /| x| /| x| x| x| x| x| x| x| /| x| o| x| /|
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
SCREEN 6| /| o| x| o| x| x| x| x| x| x| x| x| x| /| o| o|
COLOR +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
7| o| x| o| x| x| x| /| x| /| o| /| o| o| x| x| x|
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
8| /| o| o| x| x| x| x| o| x| o| x| x| x| x| x| /|
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
9| x| o| x| x| x| x| x| o| o| x| o| x| x| x| x| o|
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
10| /| /| o| x| x| x| x| /| x| o| x| x| x| x| x| /| o = EXCELLENT
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
11| o| o| x| /| x| x| x| o| x| x| x| x| o| o| /| o| / = FAIR
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
12| o| o| /| x| x| x| /| x| x| /| x| o| x| x| x| o| x = POOR
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
13| o| x| x| x| x| o| /| x| x| x| x| o| x| x| x| x|
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
14| o| o| x| o| x| x| o| x| x| x| x| /| x| x| x| /|
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
15| o| o| o| x| /| /| o| x| x| /| /| o| o| x| /| x|
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
152 PROGRAMMING GRAPHICS
~
PROGRAMMING SPRITES - ANOTHER LOOK
For those of you having trouble with graphics, this section has been
designed as a more elementary tutorial approach to sprites.
MAKING SPRITES IN BASIC - A SHORT PROGRAM
There are at least three different BASIC programming techniques which
let you create graphic images and cartoon animations on the Commodore 64.
You can use the computer's built-in graphics character set (see Page
376). You can program your own characters (see Page 108) or... best of
all... you can use the computer's built-in "sprite graphics. To
illustrate how easy it is, here's one of the shortest spritemaking
programs you can write in BASIC:
start tok64 page153.prg
10 print"{clear}"
20 poke2040,13
30 fors=832to832+62:pokes,255:next
40 v=53248
50 pokev+21,1
60 pokev+39,1
70 pokev,24
80 pokev+1,100
stop tok64
This program includes the key "ingredients" you need to create any
sprite. The POKE numbers come from the SPRITEMAKING CHART on Page 176.
This program defines the first sprite... sprite 0... as a solid white
square on the screen. Here's a line-by-line explanation of the program:
LINE 10 clears the screen.
LINE 20 sets the "sprite pointer" to where the Commodore 64 will read
its sprite data from. Sprite 0 is set at 2040, sprite 1 at 2041, sprite
2 at 2042, and so on up to sprite 7 at 2047. You can set all 8 sprite
pointers to 13 by using this line in place of line 20:
20 FOR SP=2040TO2047:POKE SP,13:NEXT SP
LINE 30 puts the first sprite (sprite 0) into 63 bytes of the Commodore
64's RAM memory starting at location 832 (each sprite requires 63 bytes
PROGRAMMING GRAPHICS 153
~
of memory). The first sprite (sprite 0) is "addressed" at memory
locations 832 to 894.
LINE 40 sets the variable "V" equal to 53248, the starting address of
the VIDEO CHIP. This entry lets us use the form (V+number) for sprite
settings. 're using the form (V+number) when POKEing sprite settings
because this format conserves memory and lets us work with smaller
numbers. For example, in line 50 we typed POKE V+21. This is the same as
typing POKE 53248+21 or POKE 53269... but V+21 requires less space than
53269, and is easier to remember.
LINE 50 enables or "turns on" sprite 0. There are 8 sprites, numbered
from 0 to 7. To turn on an individual sprite, or a combination of
sprites, all you have to do is POKE V+21 followed by a number from 0
(turn all sprites off) to 255 (turn all 8 sprites on). You can turn on
one or more sprites by POKEing the following numbers:
+------+------+------+------+------+------+------+------+------+-------+
|ALL ON|SPRT 0|SPRT 1|SPRT 2|SPRT 3|SPRT 4|SPRT 5|SPRT 6|SPRT 7|ALL OFF|
| 255 | 1 | 2 | 4 | 8 | 16 | 32 | 64 | 128 | 0 |
+------+------+------+------+------+------+------+------+------+-------+
POKE V+21,1 turns on sprite 0. POKE V+21,128 turns on sprite 7. You
can also turn on combinations of sprites. For example, POKE V+21,129
turns on both sprite 0 and sprite 7 by adding the two "turn on" numbers
(1+128) together. (See SPRITEMAKING CHART, Page 176.)
LINE 60 sets the COLOR of sprite 0. There are 16 possible sprite
colors, numbered from 0 (black) to 15 (grey). Each sprite requires a
different POKE to set its color, from V+39 to V+46. POKE V+39,1 colors
sprite 0 white. POKE V+46,15 colors sprite 7 grey. (See the SPRITEMAKING
CHART for more information.)
When you create a sprite, as you just did, the sprite will STAY IN
MEMORY until you POKE it off, redefine it, or turn off your computer.
This lets you change the color, position and even shape of the sprite in
DIRECT or IMMEDIATE mode, which is useful for editing purposes. As an
example, RUN the program above, then type this line in DIRECT mode
(without a line number) and hit the <RETURN> key:
POKE V+39,8
The sprite on the screen is now ORANGE. Try POKEing some other numbers
from 0 to 15 to see the other sprite colors. Because you did this in
154 PROGRAMMING GRAPHICS
~
DIRECT mode, if you RUN your program the sprite will return to its origi-
nal color (white).
LINE 70, determines the HORIZONTAL or "X" POSITION of the sprite on the
screen. This number represents the location of the UPPER LEFT CORNER of
the sprite. The farthest left horizontal (X) position which you can see
on your television screen is position number 24, although you can move
the sprite OFF THE SCREEN to position number 0.
LINE 80 determines the VERTICAL or "Y" POSITION of the sprite. In this
program, we placed the sprite at X (horizontal) position 24, and Y
(vertical) position 100. To try another location, type this POKE in
DIRECT mode and hit <RETURN>:
POKE V,24:POKE V+1,50
This places the sprite at the upper left corner of the screen. To move
the sprite to the lower left corner, type this:
POKE V,24:POKE V+1,229
Each number from 832 to 895 in our sprite 0 address represents one
block of 8 pixels, with three 8-pixel blocks in each horizontal row of
the sprite. The loop in line 80 tells the computer to POKE 832,255 which
makes the first 8 pixels solid . . . then POKE 833,255 to make the second
8 pixels solid, and so on to location 894 which is the last group of 8
pixels in the bottom right corner of the sprite. To better see how this
works, try typing the following in DIRECT r-node, and notice that the
second group of 8 pixels is erased:
POKE 833,0 (to put it back type POKE 833,255 or RUN your program)
The following line, which you can add to your program. erases the
blocks in the MIDDLE of the sprite you created:
90 FOR A=836 TO 891 STEP 3:POKE A,O:NEXT A
Remember, the pixels that make up the sprite are grouped in blocks of
eight. This line erases the 5th group of eight pixels (block 836) and
every third block up to block 890. Try POKEing any of the other numbers
from 832 to 894 with either a 255 to make them solid or 0 to make them
blank.
PROGRAMMING GRAPHICS 155
~
+-----------------------------------------------------------------------+
| CRUNCHING YOUR SPRITE PROGRAMS |
| |
| Here's a helpful "crunching" tip: The program described above is |
| already short, but it can be made even shorter by "crunching" it |
| smaller. In our example we list the key sprite settings on separate |
| program lines so you can see what's happening in the program. In |
| actual practice, a good programmer would probably write this program |
| as a TWO LINE PROGRAM... by "crunching" it as follows: |
| |
| 10 PRINTCHR$(147):V=53248:POKEV+21,1:POKE2040.13:POKEV+39,1 |
| 20 FORS=832TO894:POKES,255:NEXT:POKEV,24:POKEV+1,100 |
| |
| For more tips on how to crunch your programs so they fit in less |
| memory and run more efficiently, see the "crunching guide" on Page 24.|
+-----------------------------------------------------------------------+
TV SCREEN
+---------------------------------------------------+
| ^ |
| | |
|<-------+---- X POSITION = HORIZONTAL ------------>|
| | |
| | |
| | |
| | |
| | |
| | +-+ |
| | | | |
| | +-+ |
| | / |
| | / |
| | / |
| | / |
+-------------------------------/-------------------+
/
A sprite located here must have both its X-position (horizontal) and
Y-position (vertical) set so it can be displayed on the screen.
Figure 3-4. The display screen is divided into a grid of X and Y coor-
dinates.
156 PROGRAMMING GRAPHICS
~
POSITIONING SPRITES ON THE SCREEN
The entire display screen is divided into a grid of X and Y coordi-
nates, like a graph. The X COORDINATE is the HORIZONTAL position across
the screen and the Y COORDINATE is the VERTICAL position up and down (see
Figure 3-4).
To position any sprite on the screen, you must POKE TWO SETTINGS...
the X position and the Y position... these tell the computer where to
display the UPPER LEFT HAND CORNER of the sprite. Remember that a sprite
consists of 504 individual pixels, 24 across by 21 down... so if you POKE
a sprite onto the upper left corner of your screen, the sprite will be
displayed as a graphic image 24 pixels ACROSS and 21 pixels DOWN starting
at the X-Y position you defined. The sprite will be displayed based on
the upper left corner of the entire sprite, even if you define the sprite
using only a small part of the 24X21-pixel sprite area.
To understand how X-Y positioning works, study the following diagram
(Figure 3-5), which shows the X and Y numbers in relation to your display
screen. Note that the GREY AREA in the diagram shows your television
viewing area... the white area represents positions which are OFF your
viewing screen...
[THE PICTURE IS MISSING!]
PROGRAMMING GRAPHICS 157
~
To display a sprite in a given location, You must POKE the X and Y
settings for each SPRITE... remembering that every sprite has its own
unique X POKE and Y POKE. The X and Y settings for ail 8 sprites are
shown here:
POKE THESE VALUES TO SET X-Y SPRITE POSITIONS
+------+-------+-------+-------+-------+-------+-------+-------+--------+
| |SPRT 0 |SPRT 1 |SPRT 2 |SPRT 3 |SPRT 4 |SPRT 5 |SPRT 6 |SPRT 7 |
+------+-------+-------+-------+-------+-------+-------+-------+--------+
|SET X |V,X |V+2,X |V+4,X |V+6,X |V+8,X |V+10,X |V+12,X |V+14,X |
|SET Y |V+1,Y |V+3,Y |V+5,Y |V+7,Y |V+9,Y |V+11,Y |V+13,Y |V+15,Y |
|RIGHTX|V+16,1 |V+16,2 |V+16,4 |V+16,8 |V+16,16|V+16,32|V+16,64|V+16,128|
+------+-------+-------+-------+-------+-------+-------+-------+--------+
POKEING AN X POSITION: The possible values of X are 0 to 255, counting
from left to right. Values 0 to 23 place all or part of the sprite OUT OF
THE VIEWING AREA off the left side of the screen... values 24 to 255
place the sprite IN THE VIEWING AREA up to the 255th position (see next
paragraph for settings beyond the 255th X position). To place the sprite
at one of these positions, just type the X-POSITION POKE for the sprite
you're using. For example, to POKE sprite I at the farthest left X
position IN THE VIEWING AREA, type: POKE V+2,24.
X VALUES BEYOND THE 255TH POSITION: To get beyond the 255th position
across the screen, you need to make a SECOND POKE using the numbers in
the "RIGHT X" row of the chart (Figure 3-5). Normally, the horizontal (X)
numbering would continue past the 255th position to 256, 257, etc., but
because registers only contain 8 bits we must use a "second register" to
access the RIGHT SIDE of the screen and start our X numbering over again
at 0. So to get beyond X position 255, you must POKE V+16 and a number
(depending on the sprite). This gives you 65 additional X positions
(renumbered from 0 to 65) in the viewing area on the RIGHT side of the
viewing screen. (You can actually POKE the right side X value as high as
255, which takes you off the right edge of the viewing screen.)
POKEING A Y POSITION: The possible values of Y are 0 to 255, counting
from top to bottom. Values 0 to 49 place all or part of the sprite OUT
OF THE VIEWING AREA off the TOP of the screen. Values 50 to 229 place the
sprite IN THE VIEWING AREA. Values 230 to 255 place all or part of the
sprite OUT OF THE VIEWING AREA off the BOTTOM of the screen.
158 PROGRAMMING GRAPHICS
~
Let's see how this X-Y positioning works, using sprite 1. Type this
program:
start tok64 page159.prg
10 print"{clear}":v=53248:pokev+21,2:poke2041,13
20 fors=832to895:pokes,255:next:pokev+40,7
30 pokev+2,24
40 pokev+3,50
stop tok64
This simple program establishes sprite 1 as a solid box and positions it
at the upper left corner of the screen. Now change line 40 to read:
40 POKE V+3,229
This moves the sprite to the bottom left corner of the screen. Now let's
test the RIGHT X LIMIT of the sprite. Change line 30 as shown:
30 POKE V+2,255
This moves the sprite to the RIGHT but reaches the RIGHT X LIMIT, which
is 255. At this point, the "most significant bit" in register 16 must be
SET. In other words, you must type POKE V+ 16 and the number shown in the
"RIGHT X" column in the X-Y POKE CHART above to RESTART the X position
counter at the 256th pixel/position on the screen. Change line 30 as
follows:
30 POKE V+16,PEEK(V+16)OR 2:POKE V+2,0
POKE V+16,2 sets the most significant bit of the X position for sprite 1
and restarts it at the 256th pixel/position on the screen. POKE V+2,0
displays the sprite at the NEW POSITION ZERO, which is now reset to the
256th pixel.
To get back to the left side of the screen, you must reset the most
significant bit of the X position counter to 0 by typing (for sprite 1):
POKE V+16, PEEK(V+16)AND 253
TO SUMMARIZE how the X positioning works... POKE the X POSITION for any
sprite with a number from 0 to 255. To access a position beyond the 255th
position/pixel across the screen, you must use an additional POKE (V+16)
which sets the most significant bit of the X position and start counting
from 0 again at the 256th pixel across the screen.
PROGRAMMING GRAPHICS 159
~
This POKE starts the X numbering over again from 0 at the 256th position
(Example: POKE V+16,PEEK(V+16)OR 1 and POKE V,1 must be included to place
sprite 0 at the 257th pixel across the screen.) To get back to the left
side X positions you have to TURN OFF the control setting by typing
POKE V+16,PEEK(V+16)AND 254.
POSITIONING MULTIPLE SPRITES ON THE SCREEN
Here's a program which defines THREE DIFFERENT SPRITES (0, 1 and 2) in
different colors and places them in different positions on the screen:
start tok64 page160.prg
10 print"{clear}":v=53248:fors=832to895:pokes,255:next
20 form=2040to2042:pokem,13:next
30 pokev+21,7
40 pokev+39,1:pokev+40,7:pokev+41,8
50 pokev,24:pokev+1,50
60 pokev+2,12:pokev+3,229
70 pokev+4,255:pokev+5,50
stop tok64
For convenience, all 3 sprites have been defined as solid squares,
getting their data from the same place. The important lesson here is how
the 3 sprites are positioned. The white sprite 0 is at the top lefthand
corner. The yellow sprite 1 is at the bottom lefthand corner but HALF the
sprite is OFF THE SCREEN (remember, 24 is the leftmost X position in the
viewing area... an X position less than 24 puts all or part of the sprite
off the screen and we used an X position 12 here which put the sprite
halfway off the screen). Finally, the orange sprite 2 is at the RIGHT X
LIMIT (position 255)... but what if you want to display a sprite in the
area to the RIGHT of X position 255?
DISPLAYING A SPRITE BEYOND THE 255TH X-POSITION
Displaying a sprite beyond the 255th X position requires a special POKE
which SETS the most significant bit of the X position and starts over at
the 256th pixel position across the screen. Here's how it works...
First, you POKE V+16 with the number for the sprite you're using (check
the "RIGHT X" row in the X-Y chart... we'll use sprite 0). Now we assign
an X position, keeping in mind that the X counter starts over from 0 at
the 256th position on the screen. Change line 50 to read as follows:
50 POKE V+16,1:POKE V,24:POKE V+1,75
160 PROGRAMMING GRAPHICS
~
This line POKEs V+ 16 with the number required to "open up" the right
side of the screen... the new X position 24 for sprite 0 now begins 24
pixels to the RIGHT of position 255. To check the right edge of the
screen, change line 60 to:
60 POKE V+16,1:POKE V,65:POKE V+1,75
Some experimentation with the settings in the sprite chart will give
you the settings you need to position and move sprites on the left and
right sides of the screen. The section on "moving sprites" will also
increase your understanding of how sprite positioning works.
SPRITE PRIORITIES
You can actually make different sprites seem to move IN FRONT OF or
BEHIND each other on the screen. This incredible three dimensional illu-
sion is achieved by the built-in SPRITE PRIORITIES which determine which
sprites have priority over the others when 2 or more sprites OVERLAP on
the screen.
The rule is "first come, first served" which means lower-numbered
sprites AUTOMATICALLY have priority over higher-numbered sprites. For
example, if you display sprite 0 and sprite 1 so they overlap on the
screen, sprite 0 will appear to be IN FRONT OF sprite 1. Actually, sprite
0 always supersedes all the other sprites because it's the lowest num-
bered sprite. In comparison, sprite 1 has priority over sprites 2-7;
sprite 2 has priority over sprites 3-7, etc. Sprite 7 (the last sprite)
has LESS PRIORITY than any of the other sprites, and will always appear
to be displayed "BEHIND" any other sprites which overlap its position.
To illustrate how priorities work, change lines 50, 60, and 70 in the
program above to the following:
50 POKEV,24:POKEV+1,50:POKEV+16,0
60 POKEV+2,34:POKEV+3,60
70 POKEV+4,44:POKEV+5,70
You should see a white sprite on top of a yellow sprite on top of an
orange sprite. Of course, now that you see how priorities work, you can
also MOVE SPRITES and take advantage of these priorities in your ani-
mation.
PROGRAMMING GRAPHICS 161
~
DRAWING A SPRITE
Drawing a Commodore sprite is like coloring the empty spaces in a
coloring book. Every sprite consists of tiny dots called pixels. To draw
a sprite, all you have to do is "color in" some of the pixels.
Look at the spritemaking grid in Figure 3-6. This is what a blank
sprite looks like:
[THE PICTURE IS MISSING!]
Figure 3-6. Spritemaking grid.
Each little "square" represents one pixel in the sprite. There are 24
pixels across and 21 pixels up and down, or 504 pixels in the entire
sprite. To make the sprite look like something, you have to color in
these pixels using a special PROGRAM... but how can you control over 500
individual pixels? That's where computer programming can help you. In-
stead of typing 504 separate numbers, you only have to type 63 numbers
for each sprite. Here's how it works...
162 PROGRAMMING GRAPHICS
~
CREATING A SPRITE... STEP BY STEP
To make this as easy as possible for you, we've put together this
simple step by step guide to help you draw your own sprites.
STEP 1:
Write the spritemaking program shown here ON A PIECE OF PAPER... note
that line 100 starts a special DATA section of your program which will
contain the 63 numbers you need to create your sprite.
[THE PICTURE IS MISSING!]
STEP 2:
Color in the pixels on the spritemaking grid on Page 162 (or use a piece
of graph paper... remember, a sprite has 24 squares across and 21 squares
down). We suggest you use a pencil and draw lightly so you can reuse this
grid. You can create any image you like, but for our example we'll draw
a simple box.
STEP 3:
Look at the first EIGHT pixels. Each column of pixels has a number (128,
64, 32, 16, 8, 4, 2, 1). The special type of addition we are going to
show you is a type of BINARY ARITHMETIC which is used by most computers
PROGRAMMING GRAPHICS 163
~
as a special way of counting. Here's a close-up view of the first eight
pixels in the top left hand corner of the sprite:
|128| 64| 32| 16| 8| 4| 2| 1|
+---+---+---+---+---+---+---+---+
|@@@|@@@|@@@|@@@|@@@|@@@|@@@|@@@|
|@@@|@@@|@@@|@@@|@@@|@@@|@@@|@@@|
+---+---+---+---+---+---+---+---+
STEP 4:
Add up the numbers of the SOLID pixels. This first group of eight pixels
is completely solid, so the total number is 255.
STEP 5:
Enter that number as the FIRST DATA STATEMENT in line 100 of the
Spritemaking Program below. Enter 255 for the second and third groups
of eight.
STEP 6:
Look at the FIRST EIGHT PIXELS IN THE SECOND ROW of the sprite. Add up
the values of the solid pixels. Since only one of these pixels is solid,
the total value is 128. Enter this as the first DATA number in line 101.
|128| 64| 32| 16| 8| 4| 2| 1|
+---+---+---+---+---+---+---+---+
|@@@| | | | | | | |
|@@@| | | | | | | |
+---+---+---+---+---+---+---+---+
STEP 7:
Add up the values of the next group of eight pixels (which is 0 because
they're all BLANK) and enter in line 101. Now move to the next group of
pixels and repeat the process for each GROUP OF EIGHT PIXELS (there are
3 groups across each row, and 21 rows). This will give you a total of 63
numbers. Each number represents ONE group of 8 pixels, and 63 groups of
eight equals 504 total individual pixels. Perhaps a better way of looking
at the program is like this... each line in the program represents ONE
ROW in the sprite. Each of the 3 numbers in each row represents ONE GROUP
OF EIGHT PIXELS. And each number tells the computer which pixels to make
SOLID and which pixels to leave blank.
164 PROGRAMMING GRAPHICS
~
STEP 8:
CRUNCH YOUR PROGRAM INTO A SMALLER SPACE BY RUNNING TOGETHER ALL THE DATA
STATEMENTS, AS SHOWN IN THE SAMPLE PROGRAM BELOW. Note that we asked you
to write your sprite program on a piece of paper. We did this for a good
reason. The DATA STATEMENT LINES 100-120 in the program in STEP 1 are
only there to help you see which numbers relate to which groups of pixels
in your sprite. Your final program should be "crunched" like this:
start tok64 page165.prg
10 print"{clear}":poke53280,5:poke53281,6
20 v=53248:pokev+34,3
30 poke 53269,4:poke2042,13
40 forn=0to62:readq:poke832+n,q:next
100 data255,255,255,128,0,1,128,0,1,128,0,1,144,0,1,144,0,1,144,0,1,144,0
101 data1,144,0,1,144,0,1,144,0,1,144,0,1,144,0,1,144,0,1,128,0,1,128,0,1
102 data128,0,1,128,0,1,128,0,1,128,0,1,255,255,255
200 x=200:y=100:poke53252,x:poke53253,y
stop tok64
MOVING YOUR SPRITE ON THE SCREEN
Now that you've created your sprite, let's do some interesting things
with it. To move your sprite smoothly across the screen, add these two
lines to your program:
50 POKE V+5,100:FOR X=24TO255:POKE V+4,X:NEXT:POKE V+16,4
55 FOR X=0TO65:POKE V+4,X:NEXT X:POKE V+16,0:GOTO 50
LINE 50 POKEs the Y POSITION at 100 (try 50 or 229 instead for
variety). Then it sets up a FOR... NEXT loop which POKEs the sprite into
X position 0 to X position 255, in order. When it reaches the 255th
position, it POKEs the RIGHT X POSITION (POKE V+16,4) which is required
to cross to the right side of the screen.
LINE 55 has a FOR... NEXT loop which continues to POKE the sprite in
the last 65 positions on the screen. Note that the X value was reset to
zero but because you used the RIGHT X setting (POKE V+16,2) X starts over
on the right side of the screen.
This line keeps going back to itself (GOTO 50). If you just want the
sprite to move ONCE across the screen and disappear, then take out
GOTO50.
PROGRAMMING GRAPHICS 165
~
Here's a line which moves the sprite BACK AND FORTH:
50 POKE V+5,100:FOR X=24TO255:POKE V+4,X:NEXT:POKE V+16,4:
FOR X=0TO65: POKE V+4,X: NEXT X
55 FOR X=65TO0 STEP-1:POKE V+4,X:NEXT:POKE V+16,0: FOR
X=255TO24 STEP-1: POKE V+4,X:NEXT
60 GOTO 50
Do you see how these programs work? This program is the same as the
previous one, except when it reaches the end of the right side of the
screen, it REVERSES ITSELF and goes back in the other direction. That is
what the STEP-1 accomplishes... it tells the program to POKE the sprite
into X values from 65 to 0 on the right side of the screen, then from 255
to 0 on the left side of the screen, STEPping backwards minus-1 position
at a time.
VERTICAL SCROLLING
This type of sprite movement is called "scrolling." To scroll your
sprite up or down in the Y position, you only have to use ONE LINE. ERASE
LINES 50 and 55 by typing the line numbers by themselves and hitting
<RETURN> like this:
50 <RETURN>
60 <RETURN>
Now enter LINE 50 again as follows:
50 POKE V+4,24:FOR Y=0TO255:POKE V+5,Y:NEXT
THE DANCING MOUSE-A SPRITE PROGRAM EXAMPLE
Sometimes the techniques described in a programmer's reference manual
are difficult to understand, so we've put together a fun sprite program
called "Michael's Dancing Mouse." This program uses three different
sprites in a cute animation with sound effects-and to help you understand
how it works we've included an explanation of EACH COMMAND so you can see
exactly how the program is constructed:
166 PROGRAMMING GRAPHICS
~
start tok64 page167.prg
5 s=54272:pokes+24,15:pokes,220:pokes+1,68:pokes+5,15:pokes+6,215
10 pokes+7,120:pokes+8,100:pokes+12,15:pokes+13,215
15 print"{clear}":v=53248:pokev+21,1
20 fors1=12288to12350:readq1:pokes1,q1:next
25 fors2=12352to12414:readq2:pokes2,q2:next
30 fors3=12416to12478:readq3:pokes3,q3:next
35 pokev+39,15:pokev+1,68
40 printtab(160)"{white}i am the dancing mouse!{light blue}"
45 p=192
50 forx=0to347step3
55 rx=int(x/256):lx=x-rx*256
60 pokev,lx:pokev+16,rx
70 ifp=192thengosub200
75 ifp=193thengosub300
80 poke2040,p:fort=1to60:next
85 p=p+1:ifp>194thenp=192
90 next
95 end
100 data30,0,120,63,0,252,127,129,254,127,129,254,127,189,254,127,255,254
101 data63,255,252,31,187,248,3,187,192,1,255,128,3,189,192,1,231,128,1,
102 data255,0,31,255,0,0,124,0,0,254,0,1,199,32,3,131,224,7,1,192,1,192,0
103 data3,192,0,30,0,120,63,0,252,127,129,254,127,129,254,127,189,254,127
104 data255,254,63,255,252,31,221,248,3,221,192,1,255,128,3,255,192,1,195
105 data128,1,231,3,31,255,255,0,124,0,0,254,0,1,199,0,7,1,128,7,0,204,1
106 data128,124,7,128,5630,0,120,63,0,252,127,129,254,127,129,254,127,189
107 data254,127,255,25463,255,252,31,221,248,3,221,192,1,255,134,3,189
108 data204,1,199,152,1,255,48,1,255,224,1,252,0,3,254,0
109 data7,14,0,204,14,0,248,56,0,112,112,0,0,60,0,-1
200 pokes+4,129:pokes+4,128:return
300 pokes+11,129:pokes+11,128:return
stop tok64
PROGRAMMING GRAPHICS 167
~
LINE 5:
S=54272 Sets the variable 5 equal to 54272, which is the
beginning memory location of the SOUND CHIP.
From now on, instead of poking a direct memory
location, we will POKE S plus a value.
POKES+24,15 Same as POKE 54296,15 which sets VOLUME to
highest level.
POKES,220 Same as POKE 54272,220 which sets Low Fre-
quency in Voice 1 for a note which approximates
high C in Octave 6.
POKES+1,68 Same as POKE 54273,68 which sets High Fre-
quency in Voice I for a note which approximates
high C in Octave 6.
POKES+5,15 Same as POKE 54277,15 which sets Attack/Decay
for Voice 1 and in this case consists of the
maximum DECAY level with no attack, which pro-
duces the "echo" effect.
POKES+6,215 Same as POKE 54278,215 which sets Sustain/Re-
lease for Voice 1 (215 represents a combination
of sustain and release values).
LINE 10:
POKES+7,120 Same as POKE 54279,120 which sets the Low Fre-
quency for Voice 2.
POKES+8,100 Same as POKE 54280,100 which sets the High
Frequency for Voice 2.
POKES+12,15 Same as POKE 54284,15 which sets Attack/Decay
for Voice 2 to same level as Voice 1 above.
POKES+13,215 Same as POKE 54285,215 which sets Sustain/Re-
lease for Voice 2 to same level as Voice 1 above.
LINE 15:
PRINT"<SHIFT+CLR/HOME>" Clears the screen when the program begins.
V=53248 Defines the variable "V" as the starting location
of the VIC chip which controls sprites. From now
on we will define sprite locations as V plus a
value.
POKEV+21,1 Turns on (enables) sprite number 1.
168 PROGRAMMING GRAPHICS
~
LINE 20:
FORS1=12288 We are going to use ONE SPRITE (sprite 0) in this
TO 12350 animation, but we are going to use THREE sets of
sprite data to define three separate shapes. To
get our animation, we will switch the POINTERS
for sprite 0 to the three places in memory where
we have stored the data which defines our three
different shapes. The same sprite will be rede-
fined rapidly over and over again as 3 different
shapes to produce the dancing mouse animation.
You can define dozens of sprite shapes in DATA
STATEMENTS, and rotate those shapes through
one or more sprites. So you see, you don't have to
limit one sprite to one shape or vice-versa. One
sprite can have many different shapes, simply by
changing the POINTER SETTING FOR THAT SPRITE to
different places in memory where the sprite data
for different shapes is stored. This line means we
have put the DATA for "sprite shape 1" at memory
locations 12288 to 12350.
READ Q1 Reads 63 numbers in order from the DATA state-
ments which begin at line 100. Q1 is an arbitrary
variable name. It could just as easily be A, Z1 or
another numeric variable.
POKES1,Q1 Pokes the first number from the DATA statements
(the first "Q1" is 30) into the first memory
location (the first memory location is 12288). This
is the same as POKE12288,30.
NEXT This tells the computer to look BETWEEN the FOR and
NEXT parts of the loop and perform those in-between
commands (READQ1 and POKES1,Q1 using the NEXT
numbers in order). In other words, the NEXT
statement makes the computer READ the NEXT Q1 from
the DATA STATEMENTS, which is 0, and also
increments S1 by 1 to the next value, which is
12289. The result is POKE12289,0... the NEXT
command makes the loop keep going back until the
last values in the series, which are POKE 12350,0.
PROGRAMMING GRAPHICS 169
~
LINE 25:
FORS2=12352 The second shape of sprite zero is defined by the
TO 12414 DATA which is located at locations 12352 to 12414.
NOTE that location 12351 is SKIPPED... this is the
64th location which is used in the definition of
the first sprite group but does not contain any of
the sprite data numbers. Just remember when
defining sprites in consecutive locations that you
will use 64 locations, but only POKE sprite data
into the first 63 locations.
READQ2 Reads the 63 numbers which follow the numbers we
used for the first sprite shape. This READ simply
looks for the very next number in the DATA area and
starts reading 63 numbers, one at a time.
POKES2,Q2 Pokes the data (Q2) into the memory locations (S2)
for our second sprite shape, which begins at
location 12352.
NEXT Same use as line 20 above.
LINE 30:
FORS3=12416 The third shape of sprite zero is defined by the
TO 12478 DATA to be located at locations 12416 to 12478.
READQ3 Reads last 63 numbers in order as Q3.
POKES3,Q3 Pokes those numbers into locations 12416 to 12478.
NEXT Same as lines 20 and 25.
LINE 35:
POKEV+39,15 Sets color for sprite 0 to light grey.
POKEV+1,68 Sets the upper right hand corner of the sprite
square to vertical (Y) position 68. For the sake of
comparison, position 50 is the top lefthand corner
Y position on the viewing screen.
170 PROGRAMMING GRAPHICS
~
LINE 40:
PRINTTAB(160) Tabs 160 spaces from the top lefthand CHARACTER
SPACE on the screen, which is the same as 4 rows
beneath the clear command... this starts your PRINT
message on the 6th line down on the screen.
"{white} Hold down the <CTRL> key and press the key marked
<WHT> at the same time. If you do this inside
quotation marks, a "reversed E" will appear. This
sets the color to everything PRINTed from then on
to WHITE.
I AM THE This is a simple PRINT statement.
DANCING
MOUSE!
{light blue} This sets the color back to light blue when the
PRINT statement ends. Holding down <C=> and <7>
a at the same time inside quotation marks
causes a "reversed diamond symbol" to appear.
LINE 45:
P=192 Sets the variable P equal to 192. This number 192
is the pointer you must use, in this case to
"point" sprite 0 to the memory locations that begin
at location 12288. Changing this pointer to the
locations of the other two sprite shapes is the
secret of using one sprite to create an animation
that is actually three different shapes.
LINE 50:
FORX=0TO347 Steps the movement of your sprite 3 X positions at
STEP3 a time (to provide fast movement) from position 0
to position 347.
PROGRAMMING GRAPHICS 171
~
LINE 55:
RX=INT(X/256) RX is the integer of X/256 which means that RX is
rounded off to 0 when X is less than 256, and RX
becomes 1 when X reaches position 256. We will
use RX in a moment to POKE V+16 with a 0 or 1
to turn on the "RIGHT SIDE" of the screen.
LX=X-RX*256 When the sprite is at X position 0, the formula
looks like this: LX = 0 - (0 times 256) or 0. When
the sprite is at X position 1 the formula looks
like this: LX = 1 - (0 times 256) or 1. When the
sprite is at X position 256 the formula looks like
this: LX = 256 - (1 times 256) or 0 which resets X
back to 0 which must be done when you start over on
the RIGHT SIDE of the screen (POKEV+16,1).
LINE 60:
POKEV,LX You POKE V by itself with a value to set the Hori-
zontal (X) Position of sprite 0 on the screen. (See
SPRITEMAKING CHART on Page 176). As shown above,
the value of LX, which is the horizontal position
of the sprite, changes from 0 to 255 and when it
reaches 255 it automatically resets back to zero
because of the LX equation set up in line 55.
POKEV+16,RX POKEV+16 always turns on the "right side" of the
screen beyond position 256, and resets the
horizontal positioning coordinates to zero. RX is
either a 0 or a 1 based on the position of the
sprite as determined by the RX formula in line 55.
LINE 70:
IFP=192THEN If the sprite pointer is set to 192 (the first
GOSUB200 sprite shape) the waveform control for the first
sound effect is set to 129 and 128 per line 200.
172 PROGRAMMING GRAPHICS
~
LINE 75:
IFP=193THEN If the sprite pointer is set to 193 (the second
GOSUB300 sprite shape) the waveform control for the second
sound effect (Voice 2) is set to 129 and 128 per
line 300.
LINE 80:
POKE2040,P Sets the SPRITE POINTER to location 192 (remember
P=192 in line 45? Here's where we use the P).
FORT=1TO60: A simple time delay loop which sets the speed at
NEXT which the mouse dances. (Try a faster or slower
speed by increasing/decreasing the number 60.)
LINE 85:
P=P+1 Now we increase the value of the pointer by adding
1 to the original value of P.
IFP>194THEN We only want to point the sprite to 3 memory lo-
P=192 cations. 192 points to locations 12288 to 12350,
193 points to locations 12352 to 12414, and 194
points to locations 12416 to 12478. This line tells
the computer to reset P back to 192 as soon as P
becomes 195 so P never really becomes 195. P is
192, 193, 194 and then resets back to 192 and the
pointer winds up pointing consecutively to the
three sprite shapes in the three 64-byte groups of
memory locations containing the DATA.
PROGRAMMING GRAPHICS 173
~
LINE 90:
NEXTX After the sprite has become one of the 3 different
shapes defined by the DATA, only then is it allowed
to move across the screen. It will jump 3 X
positions at a time (instead of scrolling smoothly
one position at a time, which is also possible).
STEPping 3 positions at a time makes the mouse
"dance" faster across the screen. NEXT X matches
the FOR... X position loop in line 50.
LINE 95
END ENDs the program, which occurs when the sprite
moves off the screen.
LINES 100-109
DATA The sprite shapes are read from the data numbers,
in order. First the 63 numbers which comprise
sprite shape 1 are read, then the 63 numbers for
sprite shape 2, and then sprite shape 3. This data
is permanently read into the 3 memory locations and
after it is read into these locations, all the
program has to do is point sprite 0 at the 3 memory
locations and the sprite automatically takes the
shape of the data in those locations. We are
pointing the sprite at 3 locations one at a time
which produces the "animation" effect. If you want
to see how these numbers affect each sprite, try
changing the first 3 numbers in LINE 100 to 255,
255, 255. See the section on defining sprite shapes
for more information.
174 PROGRAMMING GRAPHICS
~
LINE 200:
POKES+4,129 Waveform control set to 129 turns on the sound
effect.
POKES+4,128 Waveform control set to 128 turns off the sound
effect.
RETURN Sends program back to end of line 70 after
waveform control settings are changed, to resume
program.
LINE 300:
POKES+11,129 Waveform control set to 129 turns on the sound
effect.
POKES+11,128 Waveform control set to 128 turns off the sound
effect.
RETURN Sends program back to end of line 75 to resume.
PROGRAMMING GRAPHICS 175
~
EASY SPRITEMAKING CHART
+----------+------+------+------+------+-------+-------+-------+--------+
| |SPRT 0|SPRT 1|SPRT 2|SPRT 3|SPRT 4 |SPRT 5 |SPRT 6 | SPRT 7 |
+----------+------+------+------+------+-------+-------+-------+--------+
|Turn on |V+21,1|V+21,2|V+21,4|V+21,8|V+21,16|V+21,32|V+21,64|V+21,128|
+----------+------+------+------+------+-------+-------+-------+--------+
|Put in mem| 2040,| 2041,| 2042,| 2043,| 2044, | 2045, | 2046, | 2047, |
|set point.| 192 | 193 | 194 | 195 | 196 | 197 | 198 | 199 |
+----------+------+------+------+------+-------+-------+-------+--------+
|Locations | 12288| 12352| 12416| 12480| 12544 | 12608 | 12672 | 12736 |
|for Sprite| to | to | to | to | to | to | to | to |
|Pixel | 12350| 12414| 12478| 12542| 12606 | 12670 | 12734 | 12798 |
+----------+------+------+------+------+-------+-------+-------+--------+
|Color |V+39,C|V+40,C|V+41,C|V+42,C|V+43,C |V+44,C |V+45,C |V+46,C |
+----------+------+------+------+------+-------+-------+-------+--------+
|Set LEFT X| V+0,X| V+2,X| V+4,X| V+6,X| V+8,X |V+10,X |V+12,X |V+14,X |
+----------+------+------+------+------+-------+-------+-------+--------+
|Set RIGHT |V+16,1|V+16,2|V+16,4|V+16,8|V+16,16|V+16,32|V+16,64|V+16,128|
|X position| V+0,X| V+2,X| V+4,X| V+6,X| V+8,X |V+10,X |V+12,X |V+14,X |
+----------+------+------+------+------+-------+-------+-------+--------+
|Set Y pos.| V+1,Y| V+3,Y| V+5,Y| V+7,Y| V+9,Y |V+11,Y |V+13,Y |V+15,Y |
+----------+------+------+------+------+-------+-------+-------+--------+
|Exp. Horiz|V+29,1|V+29,2|V+29,4|V+29,8|V+29,16|V+29,32|V+29,64|V+29,128|
+----------+------+------+------+------+-------+-------+-------+--------+
|Exp. Vert.|V+23,1|V+23,2|V+23,4|V+23,8|V+23,16|V+23,32|V+23,64|V+23,128|
+----------+------+------+------+------+-------+-------+-------+--------+
|Multi-Col.|V+28,1|V+28,2|V+28,4|V+28,8|V+28,16|V+28,32|V+28,64|V+28,128|
+----------+------+------+------+------+-------+-------+-------+--------+
|M-Color 1 |V+37,C|V+37,C|V+37,C|V+37,C|V+37,C |V+37,C |V+37,C |V+37,C |
+----------+------+------+------+------+-------+-------+-------+--------+
|M-Color 2 |V+38,C|V+38,C|V+38,C|V+38,C|V+38,C |V+38,C |V+38,C |V+38,C |
+----------+------+------+------+------+-------+-------+-------+--------+
|Priority | The rule is that lower numbered sprites always have display|
|of sprites| priority over higher numbered sprites. For example, sprite |
| | 0 has priority over ALL other sprites, sprite 7 has last |
| | priority. This means lower numbered sprites always appear |
| | to move IN FRONT OF or ON TOP OF higher numbered sprites. |
+----------+------------------------------------------------------------+
|S-S Collis| V+30 IF PEEK(V+30)ANDX=X THEN [action] |
+----------+------------------------------------------------------------+
|S-B Collis| V+31 IF PEEK(V+31)ANDX=X THEN [action] |
+----------+------------------------------------------------------------+
176 PROGRAMMING GRAPHICS
~
SPRITEMAKING NOTES
Alternative Sprite Memory Pointers and Memory Locations
Using Cassette Buffer
+---------------+-------+-------+-------+-------------------------------+
| Put in Memory |SPRT 0 |SPRT 1 |SPRT 2 | If you're using 1 to 3 sprites|
| (Set pointers)|2040,13|2041,14|2042,15| you can use these memory |
+---------------+-------+-------+-------+ locations in the cassette |
| Sprite Pixel | 832 | 896 | 960 | buffer (832 to 1023) but for |
| Locations for | to 894| to 958|to 1022| more than 3 sprites we suggest|
| Blocks 13-15 | | | | using locations from 12288 to |
+---------------+-------+-------+-------+ 12798 (see chart). |
TURNING ON SPRITES: +-------------------------------+
You can turn on any individual sprite by using POKE V+21 and the number
from the chart... BUT... turning on just ONE sprite will turn OFF any
others. To turn on TWO OR MORE sprites, ADD TOGETHER the numbers of the
sprites you want to turn on (Example: POKE V+21, 6 turns on sprites 1 and
2). Here is a method you can use to turn one sprite off and on without
affecting any of the others (useful for animation).
EXAMPLE:
To turn off just sprite 0 type: POKE V+21,PEEK V+21AND(255-1). Change
the number 1 in (255-1) to 1,2,4,8,16,32,64, or 128 (for sprites 0-7). To
re-enable the sprite and not affect the other sprites currently turned
on, POKE V+21, PEEK(V+21)OR 1 and change the OR 1 to OR 2 (sprite 2), OR
4 (sprite 3), etc.
X POSITION VALUES BEYOND 255:
X positions run from 0 to 255... and then START OVER from 0 to 255. To
put a sprite beyond X position 255 on the far right side of the screen,
you must first POKE V+ 16 as shown, THEN POKE a new X valve from 0 to 63,
which will place the sprite in one of the X positions at the right side
of the screen. To get back to positions 0-255, POKE V+16,0 and POKE in an
X value from 0 to 255.
Y POSITION VALUES:
Y positions run from 0 to 255, including 0 to 49 off the TOP of the
viewing area, 50 to 229 IN the,viewing area, and 230 to 255 off the
BOTTOM of the viewing area.
PROGRAMMING GRAPHICS 177
~
SPRITE COLORS:
To make sprite 0 WHITE, type: POKE V+39,1 (use COLOR POKE SETTING shown
in chart, and INDIVIDUAL COLOR CODES shown below):
0-BLACK 4-PURPLE 8-ORANGE 12-MED. GREY
1-WHITE 5-GREEN 9-BROWN 13-LT. GREEN
2-RED 6-BLUE 10-LT. RED 14-LT. BLUE
3-CYAN 7-YELLOW 11-DARK GREY 15-LT. GREY
MEMORY LOCATION:
You must "reserve" a separate 64-BYTE BLOCK of numbers in the
computer's memory for each sprite of which 63 BYTES will be used for
sprite data. The memory settings shown below are recommended for the
"sprite pointer" settings in the chart above. Each sprite will be unique
and you'll have to define it as you wish. To make all sprites exactly the
same, point the sprites you want to look the same to the same register
for sprites.
DIFFERENT SPRITE POINTER SETTINGS:
These sprite pointer settings are RECOMMENDATIONS ONLY.
Caution: you can set your sprite pointers anywhere in RAM memory but if
you set them too "low" in memory a long BASIC program may overwrite your
sprite data, or vice versa. To protect an especially LONG BASIC PROGRAM
from overwriting sprite data, you may want to set the sprites at a higher
area of memory (for example, 2040,192 for sprite 0 at locations 12288 to
12350... 2041,193 at locations 12352 to 12414 for sprite 1 and so on...
by adjusting the memory locations from which sprites get their "data,"
you can define as many as 64 different sprites plus a sizable BASIC
program. To do this, define several sprite "shapes" in your DATA
statements and then redefine a particular sprite by changing the
"pointer" so the sprite you are using is "pointed" at different areas of
memory containing different sprite picture data. See the "Dancing Mouse"
to see how this works. If you want two or more sprites to have THE SAME
SHAPE (you can still change position and color of each sprite), use the
same sprite pointer and memory location for the sprites you want to match
(for example, you can point sprites 0 and 1 to the same location by using
POKE 2040,192 and POKE 2041, 192).
178 PROGRAMMING GRAPHICS
~
PRIORITY:
Priority means one sprite will appear to move "in front of" or "behind"
another sprite on the display screen. Sprites with more priority always
appear to move "in front of" or "on top of" sprites with less priority.
The rule is that lower numbered sprites have priority over higher
numbered sprites. Sprite 0 has priority over all other sprites. Sprite 7
has no priority in relation to the other sprites. Sprite 1 has priority
over sprites 2-7, etc. If you put two sprites in the some position, the
sprite with the higher priority will appear IN FRONT OF the sprite with
the lower priority. The sprite with lower priority will either be
obscured, or will "show through" (from "behind") the sprite with higher
priority.
USING MULTI-COLOR:
You can create multi-colored sprites although using multi-color mode
requires that you use PAIRS of pixels instead of individual pixels in
your sprite picture (in other words each colored "dot" or "block" in the
sprite will consist of two pixels side by side). You have 4 colors to
choose from: Sprite Color (chart,above), Multi-Color 1, Multi-Color 2 and
"Background Color" (background is achieved by using zero settings which
let the background color "show through"). Consider one horizontal 8-pixel
block in a sprite picture. The color of each PAIR of pixels is determined
according to whether the left, right, or both pixels are solid, like
this:
+-+-+
| | | BACKGROUND (Making BOTH PIXELS BLANK (zero) lets the
+-+-+ INNER SCREEN COLOR (background)show through.)
+-+-+
| |@| MULTI-COLOR 1 (Making the RIGHT PIXEL SOLID in a pair of pixels
+-+-+ sets BOTH PIXELS to Multi-Color 1.)
+-+-+
|@| | SPRITE COLOR (Making the LEFT PIXEL SOLID in a pair of pixels
+-+-+ sets BOTH PIXELS to Sprite Color.)
+-+-+
|@|@| MULTI-COLOR 2 (Making BOTH PIXELS SOLID in a pair of pixels
+-+-+ sets BOTH PIXELS to Multi-Color 2.)
PROGRAMMING GRAPHICS 179
~
Look at the horizontal 8-pixel row shown below. This block sets the first
two pixels to background color, the second two pixels to Multi-Color 1,
the third two pixels to Sprite Color and the fourth two pixels to Multi-
Color 2. The color of each PAIR of pixels depends on which bits in each
pair are solid and which are blank, according to the illustration above.
After you determine which colors you want in each pair of pixels, the
next step is to add the values of the solid pixels in the 8-pixel block,
and POKE that number into the proper memory location. For example, if the
8-pixel row shown below is the first block in a sprite which begins at
memory location 832, the value of the solid pixels is 16+8+2+1 27, so you
would POKE 832,27.
|128| 64| 32| 16| 8| 4| 2| 1| 16+8+2+1 = 27
+---+---+---+---+---+---+---+---+
| | | |@@@|@@@| |@@@|@@@|
| | | |@@@|@@@| |@@@|@@@|
+---+---+---+---+---+---+---+---+
LOOKS LIKE THIS IN SPRITE
+-------+-------+-------+-------+
|BACKGR.|MULTI- |SPRITE |MULTI- |
| COLOR |COLOR 1| COLOR |COLOR 2|
+-------+-------+-------+-------+
COLLISION:
You can detect whether a sprite has collided with another sprite by
using this line: IF PEEK(V+30)ANDX=XTHEN [insert action here]. This line
checks to see if a particular sprite has collided with ANY OTHER SPRITE,
where X equals 1 for sprite 0, 2 for sprite 1, 4 for sprite 2, 8 for
sprite 3, 16 for sprite 4, 32 for sprite 5, 64 for sprite 6, and 128 for
sprite 7. To check to see if the sprite has collided with a "BACKGROUND
CHARACTER" use this line: IF PEEK(V+31)ANDX=XTHEN [insert action here].
180 PROGRAMMING GRAPHICS
~
USING GRAPHIC CHARACTERS IN DATA STATEMENTS
The following program allows you to create a sprite using blanks and
solid circles <SHIFT+Q> in DATA statements. The sprite and the numbers
POKED into the sprite data registers are displayed.
start tok64 page181.prg
10 print"{clear}":fori=0to63:poke832+i,0:next
20 gosub60000
999 end
60000 data" QQQQQQQ "
60001 data" QQQQQQQQQQQ "
60002 data" QQQQQQQQQQQQQ "
60003 data" QQQQQ QQQQQ "
60004 data" QQQQQ QQQ QQQQ "
60005 data" QQQQQ QQQ QQQQQ "
60006 data" QQQQQ QQQ QQQQ "
60007 data" QQQQQ QQQQQ "
60008 data" QQQQQQQQQQQQQ "
60009 data" QQQQQQQQQQQQQ "
60010 data" Q QQQQQQQQQ Q "
60011 data" Q QQQQQQQ Q "
60012 data" Q QQQQQ Q "
60013 data" Q QQQ Q "
60014 data" Q QQQ Q "
60015 data" Q Q Q "
60016 data" Q Q Q "
60017 data" QQQQQ "
60018 data" QQQQQ "
60019 data" QQQQQ "
60020 data" QQQ "
60100 v=53248:pokev,200:pokev+1,100:pokev+21,1:pokev+39,14:poke2040,13
60105 pokev+23,1:pokev+29,1
60110 fori=0to20:reada$:fork=0to2:t=0:forj=0to7:b=0
60140 ifmid$(a$,j+k*8+1,1)="Q"thenb=1
60150 t=t+b*2^(7-j):next:printt;:poke832+i*3+k,t:next:print:next
60200 return
stop tok64
PROGRAMMING GRAPHICS 181
~~
CHAPTER 4
PROGRAMMING
SOUND AND
MUSIC ON YOUR
COMMODORE 64
o Introduction
Volume Control
Frequencies of Sound Waves
o Using Multiple Voices
o Changing Waveforms
o The Envelope Generator
o Filtering
o Advanced Techniques
o Synchronization and Ring
Modulation
183
~
INTRODUCTION
Your Commodore computer is equipped with one of the most sophisticated
electronic music synthesizers available on any computer. It comes
complete with three voices, totally addressable, ATTACK/DECAY/SUSTAIN/
RELEASE (ADSR), filtering, modulation, and "white noise." All of these
capabilities are directly available for you through a few easy to use
BASIC and/or assembly language statements and functions. This means that
you can make very complex sounds and songs using programs that are
relatively simple to design.
This section of your Programmer's Reference Guide has been created to
help you explore all the capabilities of the 6581 "SID" chip, the sound
and music synthesizer inside your Commodore computer. We'll explain both
the theory behind musical ideas and the practical aspects of turning
those ideas into real finished songs on your Commodore computer.
You need not be an experienced programmer nor a music expert to achieve
exciting results from the music synthesizer. This section is full of
programming examples with complete explanations to get you started.
You get to the sound generator by POKEing into specified memory
locations. A full list of the locations used is provided in Appendix O.
We will go through each concept, step by step. By the end you should be
able to create an almost infinite variety of sounds, and be ready to
perform experiments with sound on your own.
Each section of this chapter begins by giving you an example and a full
line-by-line description of each program, which will show you how to use
the characteristic being discussed. The technical explanation is for you
to read whenever you are curious about what is actually going on. The
workhorse of your sound programs is the POKE statement. POKE sets the
indicated memory location (MEM) equal to a specified value (NUM).
POKE MEM,NUM
The memory locations (MEM) used for music synthesis start at 54272
($D400) in the Commodore 64. The memory locations 54272 to 54296
inclusive are the POKE locations you need to remember when you're using
the 6581 (SID) chip register map. Another way to use the locations above
is to remember only location 54272 and then add a number from 0 through
24 to it. By doing this you can POKE all the locations from 54272 to
54296 that you need from the SID chip. The numbers (NUM) that you use in
your POKE statement must be between 0 and 255, inclusive.
184 PROGRAMMING SOUND AND MUSIC
~
When you've had a little more practice with making music, then you can
get a little more involved, by using the PEEK function. PEEK is a
function that is equal to the value currently in the indicated memory
location.
X=PEEK(MEM)
The value of the variable X is set equal to the current contents of
memory location MEM.
Of course, your programs include other BASIC commands, but for a full
explanation of them, refer to the BASIC Statements section of this
manual.
Let's jump right in and try a simple program using only one of the
three voices. Computer ready? Type NEW, then type in this program, and
save it on your Commodore DATASSETTE(TM) or disk. Then, RUN it.
EXAMPLE PROGRAM 1:
start tok64 page185.prg
5 s=54272
10 forl=stos+24:pokel,0:next:rem clear sound chip
20 pokes+5,9:pokes+6,0
30 pokes+24,15 :rem set volume to maximum
40 readhf,lf,dr
50 ifhf<0thenend
60 pokes+1,hf:pokes,lf
70 pokes+4,33
80 fort=1todr:next
90 pokes+4,32:fort=1to50:next
100 goto40
110 data25,177,250,28,214,250
120 data25,177,250,25,177,250
130 data25,177,125,28,214,125
140 data32,94,750,25,177,250
150 data28,214,250,19,63,250
160 data19,63,250,19,63,250
170 data21,154,63,24,63,63
180 data25,177,250,24,63,125
190 data19,63,250,-1,-1,-1
stop tok64
Here's a line-by-line description of the program you've just typed in.
Refer to it whenever you feel the need to investigate parts of the pro-
gram that you don't understand completely.
PROGRAMMING SOUND AND MUSIC 185
~
LINE-BY-LINE EXPLANATION OF EXAMPLE PROGRAM 1:
+--------+--------------------------------------------------------------+
| Line(s)| Description |
+--------+--------------------------------------------------------------+
| 5 | Set S to start of sound chip. |
| 10 | Clear all sound chip registers. |
| 20 | Set Attack/Decay for voice 1 (A=O,D=9). |
| | Set Sustain/Release for voice 1 (S=O,R=O), |
| 30 | Set volume at maximum. |
| 40 | Read high frequency, low frequency, duration of note. |
| 50 | When high frequency less than zero, song is over. |
| 60 | Poke high and low frequency of voice 1. |
| 70 | Gate sawtooth waveform for voice 1. |
| 80 | Timing loop for duration of note. |
| 90 | Release sawtooth waveform for voice 1. |
| 100 | Return for next note. |
| 110-180| Data for song: high frequency, low frequency, duration |
| | (number of counts) for each note. |
| 190 | Last note of song and negative Is signaling end of song. |
+--------+--------------------------------------------------------------+
VOLUME CONTROL
Chip register 24 contains the overall volume control. The volume can be
set anywhere between 0 and 15. The other four bits are used for purposes
we'll get into later. For now it is enough to know volume is 0 to 15.
Look at line 30 to see how it's set in Example Program 1.
FREQUENCIES OF SOUND WAVES
Sound is created by the movement of air in waves. Think of throwing a
stone into a pool and seeing the waves radiate outward. When similar
waves are created in air, we hear it. If we measure the time between one
peak of a wave and the next, we find the number of seconds for one cycle
of the wave (n = number of seconds). The reciprocal of this number (1/n)
gives you the cycles per second. Cycles per second are more commonly
known as the frequency. The highness or lowness of a sound (pitch) is
determined by the frequency of the sound waves produced.
The sound generator in your Commodore computer uses two locations to
determine the frequency. Appendix E gives you the frequency values you
need to reproduce a full eight octaves of musical notes. To create a
186 PROGRAMMING SOUND AND MUSIC
~
frequency other than the ones listed in the note table use "Fout" (fre-
quency output) and the following formula to represent the frequency (Fn)
of the sound you want to create. Remember that each note requires both a
high and a low frequency number.
Fn = Fout/.06097
Once you've figured out what Fn is for your "new" note the next step is
to create the high and low frequency values for that note. To do this you
must first round off Fn so that any numbers to the right of the decimal
point are left off. You are now left with an integer value. Now you can
set the high frequency location (Fhi) by using the formula
Fhi=INT(Fn/256) and the low frequency location (Flo) should be
Flo=Fn-(256*Fhi).
At this point you have already played with one voice of your computer.
If you wanted to stop here you could find a copy of your favorite tune
and become the maestro conducting your own computer orchestra in your "at
home" concert hall.
USING MULTIPLE VOICES
Your Commodore computer has three independently controlled voices
(oscillators). Our first example program used only one of them. later on,
you'll learn how to change the quality of the sound made by the voices.
But right now, let's get all three voices singing.
This example program shows you one way to translate sheet music for
your computer orchestra. Try typing it in, and then SAVE it on your
DATASSETTE(TM) or disk. Don't forget to type NEW before typing in this
program.
EXAMPLE PROGRAM 2:
start tok64 page187.prg
10 s=54272:forl=stos+24:pokel,0:next
20 dimh(2,200),l(2,200),c(2,200)
30 dimfq(11)
40 v(0)=17:v(1)=65:v(2)=33
50 pokes+10,8:pokes+22,128:pokes+23,244
60 fori=0to11:readfq(i):next
100 fork=0to2
110 i=0
120 readnm
130 ifnm=0then250
140 wa=v(k):wb=wa-1:ifnm<0thennm=-nm:wa=0:wb=0
150 dr%nm/128:oc%=(nm-128*dr%)/16
160 nt=nm-128*dr%-16*oc%
170 fr=fq(nt)
180 ifoc%=7then200
190 forj=6tooc%step-1:fr=fr/2:next
200 hf%=fr/256:lf%=fr-256*hf%
210 ifdr%=1thenh(k,i)=hf%:l(k,i)=lf%:c(k,i)=wa:i=i+1:goto120
220 forj=1todr%-1:h(k,i)=hf%:l(k,i)=lf%:c(k,i)=wa:i=i+1:next
230 h(k,i)=hf%:l(k,i)=lf%:c(k,i)=wb
240 i=i+1:goto120
250 ifi>imthenim=i
260 next
500 pokes+5,0:pokes+6,240
510 pokes+12,85:pokes+13,133
520 pokes+19,10:pokes+20,197
530 pokes+24,31
540 fori=0toim
550 pokes,l(0,i):pokes+7,l(1,i):pokes+14,l(2,i)
560 pokes+1,h(0,i):pokes+8,h(1,i):pokes+15,h(2,i)
570 pokes+4,c(0,i):pokes+11,c(1,i):pokes+18,c(2,i)
580 fort=1to80:next:next
590 fort=1to200:next:pokes+24,0
600 data34334,36376,38539,40830
610 data43258,45830,48556,51443
620 data54502,57743,61176,64814
1000 data594,594,594,596,596,1618,587,592,587.585,331,336
1010 data1097,583,585,585,585,587,587,1609,585,331,337,594,594,593
1020 data1618,594,596,594,592,587,1616,587,585,331,336,841,327
1999 data1607,0
2000 data583,585,583,583,327,329,1611,583,585,578,578,578
2010 data196,198,583,326,578,326,327,329,327,329,326,578,583
2020 data1606,582,322,324,582,587,329,327,1606,583,327,329,587,331,329
2999 data329,328,1609,578,834,324,322,327,585,1602,0
3000 data567,566,567,304,306,308,310,1591,567,311,310,567
3010 data306,304,299,308,304,171,176,306,291,551,306,308
3020 data310,308,310,306,295,297,299,304,1586,562,567,310,315,311
3030 data308,313,297,1586,567,560,311,309,308,309,306,308
3999 data1577,299,295,306,310,311,304,562,546,1575,0
stop tok64
188 PROGRAMMING SOUND AND MUSIC
~
Here is a line,-by-line explanation of Example Program 2. For now, we
are interested in how the three voices are controlled.
LINE-BY-LINE EXPLANATION OF EXAMPLE PROGRAM 2:
+---------+-------------------------------------------------------------+
| Line(s) | Description |
+---------+-------------------------------------------------------------+
| 10 | Set S equal to start of sound chip and clear all sound |
| | chip registers. |
| 20 | Dimension arrays to contain activity of song, 1/16th of a |
| | measure per location. |
| 30 | Dimension array to contain base frequency for each note. |
| 40 | Store waveform control byte for each voice. |
| 50 | Set high pulse width for voice 2. |
| | Set high frequency for filter cutoff. |
| | Set resonance for filter and filter voice 3. |
| 60 | Read in base frequency for each note. |
| 100 | Begin decoding loop for each voice. |
| 110 | Initialize pointer to activity array. |
| 120 | Read coded note. |
| 130 | If coded note is zero, then next voice. |
| 140 | Set waveform controls to proper voice. |
| | If silence, set waveform controls to 0. |
| 150 | Decode duration and octave. |
| 160 | Decode note. |
| 170 | Get base frequency for this note. |
| 180 | If highest octave, skip division loop. |
| 190 | Divide base frequency by 2 appropriate number of times. |
| 200 | Get high and low frequency bytes. |
| 210 | If sixteenth note, set activity array: high frequency, low |
| | frequency, and waveform control (voice on). |
| 220 | For all but last beat of note, set activity array: high |
| | frequency, low frequency, waveform control (voice on). |
| 230 | For last beat of note, set activity array: high frequency, |
| | low frequency, waveform control (voice off). |
| 240 | Increment pointer to activity array. Get next note. |
| 250 | If longer than before, reset number of activities. |
| 260 | Go back for next voice. |
| 500 | Set Attack/Decay for voice 1 (A=0, D=0). |
| | Set Sustain/Release for voice 1 (S=15, R=0). |
PROGRAMMING SOUND AND MUSIC 189
~
+---------+-------------------------------------------------------------+
| Line(s) | Description |
+---------+-------------------------------------------------------------+
| 510 | Set Attack/Decay for voice 2 (A=5, D=5). |
| | Set Sustain/Release for voice 2 (S=8, R=5). |
| 520 | Set Attack/Decay for voice 3 (A=O, D=10). |
| | Set Sustain/Release for voice 3 (S=12, R=5). |
| 530 | Set volume 15, low-pass filtering. |
| 540 | Start loop for every 1/16th of a measure. |
| 550 | POKE low frequency from activity array for all voices. |
| 560 | POKE high frequency from activity array for all voices. |
| 570 | POKE waveform control from activity array for all voices. |
| 580 | Timing loop for 1/16th of a measure and back for next |
| | 1/16th measure. |
| 590 | Pause, then turn off volume. |
| 600-620 | Base frequency data. |
|1000-1999| Voice 1 data. |
|2000-2999| Voice 2 data. |
|3000-3999| Voice 3 data. |
+-----------------------------------------------------------------------+
The values used in the data statements were found by using the note
table in Appendix E and the chart below:
+-----------------+------------+
| NOTE TYPE | DURATION |
+-----------------+------------+
| 1/16 | 128 |
| 1/8 | 256 |
| DOTTED 1/8 | 384 |
| 1/4 | 512 |
| 1/4+1/16 | 640 |
| DOTTED 1/4 | 768 |
| 1/2 | 1024 |
| 1/2+1/16 | 1152 |
| 1/2+1/8 | 1280 |
| DOTTED 1/2 | 1536 |
| WHOLE | 2048 |
+-----------------+------------+
190 PROGRAMMING SOUND AND MUSIC
~
The note number from the note table is added to the duration above.
Then each note can be entered using only one number which is decoded by
your program. This is only one method of coding note values. You may be
able to come up with one with which you are more comfortable. The formula
used here for encoding a note is as follows:
1) The duration (number of 1/16ths of a measure) is multiplied by 8.
2) The result of step 1 is added to the octave you've chosen (0-7).
3) The result of step 2 is then multiplied by 16.
4) Add your note choice (0-11) to the result of the operation in step
3.
In other words:
((((D*8)+O)*16)+N)
Where D = duration, O = octave, and N = note
A silence is obtained by using the negative of the duration number
(number of 1/16ths of a measure * 128).
CONTROLLING MULTIPLE VOICES
Once you have gotten used to using more than one voice, you will find
that the timing of the three voices needs to be coordinated. This is ac-
complished in this program by:
1) Divide each musical measure into 16 parts.
2) Store the events that occur in each 1/16th measure interval in three
separate arrays.
The high and low frequency bytes are calculated by dividing the fre-
quencies of the highest octave by two (lines 180 and 190). The waveform
control byte is a start signal for beginning a note or continuing a note
that is already playing. It is a stop signal to end a note. The waveform
choice is made once for each voice in line 40.
Again, this is only one way to control multiple voices. You may come
up with your own methods. However, you should now be able to take any
piece of sheet music and figure out the notes for all three voices.
PROGRAMMING SOUND AND MUSIC 191
~
CHANGING WAVEFORMS
The tonal quality of a sound is called the timbre. The timbre of a
sound is determined primarily by its "waveform." If you remember the
example of throwing a pebble into the water you know that the waves
ripple evenly across the pond. These waves almost look like the first
sound wave we're going to talk about, the sinusoidal wave, or sine wave
for short (shown below).
+ +
+ + + +
/ \ / \
./.......\......./.......\.
\ /
+ +
+
To make what we're talking about a bit more practical, let's go back to
the first example program to investigate different waveforms. The reason
for this is that you can hear the changes more easily using only one
voice. LOAD the first music program that you typed in earlier, from your
DATASSETTE(TM) or disk, and RUN it again. That program is using the
sawtooth waveform (shown here)
+ + +
/| /| /|
/ | / | / |
/ | / | / |
./...|.../...|.../...|.....
| / | / | /
| / | / | /
|/ |/ |/
+ + +
from the 6581 SID chip's sound generating device. Try changing the note
start number in line 70 from 33 to 17 and the note stop number in line 90
from 32 to 16. Your program should now look like this:
192 PROGRAMMING SOUND AND MUSIC
~
EXAMPLE PROGRAM 3 (EXAMPLE 1 MODIFIED):
start tok64 page193.prg
5 s=54272
10 forl=stos+24:pokel,0:next
20 pokes+5,9:pokes+6,0
30 pokes+24,15
40 readhf,lf,dr
50 ifhf<0thenend
60 pokes+1,hf:pokes,lf
70 pokes+4,17
80 fort=1todr:next
90 pokes+4,16:fort=1to50:next
100 goto40
110 data25,177,250,28,214,250
120 data25,177,250,25,177,250
130 data25,177,125,28,214,125
140 data32,94,750,25,177,250
150 data28,214,250,19,63,250
160 data19,63,250,19,63,250
170 data21,154,63,24,63,63
180 data25,177,250,24,63,125
190 data19,63,250,-1,-1,-1
stop tok64
Now RUN the program.
Notice how the sound quality is different, less twangy, more hollow.
That's because we changed the sawtooth waveform into a triangular
waveform (shown left). The third musical waveform is called a variable
pulse wave (shown right).
+ + +----+ +----+ +----+ |
/ \ / \ | | | | | | |
/ \ / \ | | | | | | |
/ \ / \ | | | | | | |
./.......\......./.......\. .|....|..|....|..|....|..|.
\ / | | | | | | |
\ / | | | | | | |
\ / | | | | | | |
+ | +--+ +--+ +--+
<-->
PULSE WIDTH
PROGRAMMING SOUND AND MUSIC 193
~
It is a rectangular wave and you determine the length of the pulse
cycle by defining the proportion of the wave which will be high. This is
accomplished for voice 1 by using registers 2 and 3: Register 2 is the
low byte of the pulse width (Lpw = 0 through 255). Register 3 is the high
4 bits (Hpw = 0 through 15).
Together these registers specify a 12-bit number for your pulse width,
which you can determine by using the following formula:
PWn = Hpw*256 + Lpw
The pulse width is determined by the following equation:
PWout = (PWn/40.95) %
When PWn has a value of 2048, it will give you a square wave. That
means that register 2 (Lpw) = 0 and register 3 (Hpw) = 8.
Now try adding this line to your program:
15 POKES+3,8:POKES+2,0
Then change the start number in line 70 to 65 and the stop number in fine
90 to 64, and RUN the program. Now change the high pulse width (register
3 in line 15) from an 8 to a 1. Notice how dramatic the difference in
sound quality is?
The last waveform available to you is white noise (shown here).
. . .
. . . . .
. . . .
...........................
. . . .
. . . .
. . .
It is used mostly for sound effects and such. To hear how it sounds, try
changing the start number in line 70 to 129 and the stop number in line
90 to 128.
UNDERSTANDING WAVEFORMS
When a note is played, it consists of a sine wave oscillating at the
fundamental frequency and the harmonics of that wave.
194 PROGRAMMING SOUND AND MUSIC
~
The fundamental frequency defines the overall pitch of the note.
Harmonics are sine waves having frequencies which are integer multiples
of the fundamental frequency. A sound wave is the fundamental frequency
and all of the harmonics it takes to make up that sound.
[THE PICTURE IS MISSING!]
In musical theory let's say that the fundamental frequency is harmonic
number 1. The second harmonic has a frequency twice the fundamental
frequency, the third harmonic is three times the fundamental frequency,
and so on. The amounts of each harmonic present in a note give it its
timbre.
An acoustic instrument, like a guitar or a violin, has a very compli-
cated harmonic structure. In fact, the harmonic structure may vary as a
single note is played. You have already played with the waveforms
available in your Commodore music synthesizer. Now let's talk about how
the harmonics work with the triangular, sawtooth, and rectangular waves.
A triangular wave contains only odd harmonics. The amount of each
harmonic present is proportional to the reciprocal of the square of the
harmonic number. In other words harmonic number 3 is 1/9 quieter than
harmonic number 1, because the harmonic 3 squared is 9 (3 X 3) and the
reciprocal of 9 is 1/9.
As you can see, there is a similarity in shape of a triangular wave to
a sine wave oscillating at the fundamental frequency.
Sawtooth waves contain all the harmonics. The amount of each harmonic
present is proportional to the reciprocal of the harmonic number. For
example, harmonic number 2 is 1/2 as loud as harmonic number 1.
The square wave contains odd harmonics in proportion to the reciprocal
of the harmonic number. Other rectangular waves have varying harmonic
content. By changing the pulse width, the timbre of the sound of a
rectangular wave can be varied tremendously.
PROGRAMMING SOUND AND MUSIC 195
~
By choosing carefully the waveform used, you can start with a harmonic
structure that looks somewhat like the sound you want. To refine the
sound, you can add another aspect of sound quality available on your
Commodore 64 called filtering, which we'll discuss later in this section.
THE ENVELOPE GENERATOR
The volume of a musical tone changes from the moment you first hear it,
all the way through until it dies out and you can't hear it anymore. When
a note is first struck, it rises from zero volume to its peak volume. The
rate at which this happens is called the ATTACK. Then, it fails from the
peak to some middle-ranged volume. The rate at which the fall of the note
occurs is called the DECAY. The mid-ranged volume itself is called the
SUSTAIN level. And finally, when the note stops playing, it fails from
the SUSTAIN level to zero volume. The rate at which it fails is called
the RELEASE. Here is a sketch of the four phases of a note:
+
/ \
/ \
/ \
SUSTAIN LEVEL . ./. . . .+--------+
/ \
/ \
/ \
| | | | |
| A | D | S | R |
Each of the items mentioned above give certain qualities and restric-
tions to a note. The bounds are called parameters.
The parameters ATTACK/DECAY/SUSTAIN/RELEASE and collectively called
ADSR, can be controlled by your use of another set of locations in the
sound generator chip. LOAD your first example program again. RUN it again
and remember how it sounds. Then, changing line 20 so the program is like
this:
196 PROGRAMMING SOUND AND MUSIC
~
EXAMPLE PRO6RAM 4 (EXAMPLE 1 MODIFIED):
start tok64 page197.prg
5 s=54272
10 forl=stos+24:pokel,0:next
20 pokes+5,88:pokes+6,195
30 pokes+24,15
40 readhf,lf,dr
50 ifhf<0thenend
60 pokes+1,hf:pokes,lf
70 pokes+4,33
80 fort=1todr:next
90 pokes+4,32:fort=1to50:next
100 goto40
110 data25,177,250,28,214,250
120 data25,177,250,25,177,250
130 data25,177,125,28,214,125
140 data32,94,750,25,177,250
150 data28,214,250,19,63,250
160 data19,63,250,19,63,250
170 data21,154,63,24,63,63
180 data25,177,250,24,63,125
190 data19,63,250,-1,-1,-1
stop tok64
Registers 5 and 6 define the ADSR for voice 1. The ATTACK is the high
nybble of register 5. Nybble is half a byte, in other words the lower 4
or higher 4 on/off locations (bits) in each register. DECAY is the low
nybble. You can pick any number 0 through 15 for ATTACK, multiply it by
16 and add to any number 0 through 15 for DECAY. The values that
correspond to these numbers are listed below.
SUSTAIN level is the high nybble of register 6. It can be 0 through 15.
It defines the proportion of the peak volume that the SUSTAIN level will
be. RELEASE rate is the low nybble of register 6.
PROGRAMMING SOUND AND MUSIC 197
~
Here are the meanings of the values for ATTACK, DECAY, and RELEASE:
+-----+------------------------+--------------------------------+
|VALUE|ATTACK RATE (TIME/CYCLE)| DECAY/RELEASE RATE (TIME/CYCLE)|
+-----+------------------------+--------------------------------+
| 0 | 2 ms | 6 ms |
| 1 | 8 ms | 24 ms |
| 2 | 16 ms | 48 ms |
| 3 | 24 ms | 72 ms |
| 4 | 38 ms | 114 ms |
| 5 | 56 ms | 168 ms |
| 6 | 68 ms | 204 ms |
| 7 | 80 ms | 240 ms |
| 8 | 100 ms | 300 ms |
| 9 | 250 ms | 750 ms |
| 10 | 500 ms | 1.5 s |
| 11 | 800 ms | 2.4 s |
| 12 | 1 s | 3 s |
| 13 | 3 s | 9 s |
| 14 | 5 s | 15 s |
| 15 | 8 s | 24 s |
+-----+------------------------+--------------------------------+
Here are a few sample settings to try in your example program. Try
these and a few of your own. The variety of sounds you can produce is
astounding! For a violin type sound, try changing line 20 to read:
20 POKES+5,88:POKES+6,89:REM A=5;D=8;S=5;R=9
Change the waveform to triangle and get a xylophone type sound by using
these lines:
20 POKES+5,9:POKES+6,9:REM A=0;D=9;S=O;R=9
70 POKES+4,17
90 POKES+4,16:FORT=1TO50:NEXT
198 PROGRAMMING SOUND AND MUSIC
~
Change the waveform to square and try a piano type sound with these
lines:
15 POKES+3,8:POKES+2,0
20 POKES+5,9:POKES+6,0: REM A=0;D=9;S=0;R=0
70 POKES+4,65
90 POKES+4,64:FORT=1TO50:NEXT
The most exciting sounds are those unique to the music synthesizer
itself, ones that do not attempt to mimic acoustic instruments. For
example try:
20 POKES+5,144:POKES+6,243:REM A=9;D=O; S=15;R=3
FILTERING
The harmonic content of a waveform can be changed by using a filter.
The SID chip is equipped with three types of filtering. They can be used
separately or in combination with one another. Let's go back to the
sample program you've been using to play with a simple example that uses
a filter. There are several filter controls to set.
You add line 15 in the program to set the cutoff frequency of the
filter. The cutoff frequency is the reference point for the filter. You
SET the high and low frequency cutoff points in registers 21 and 22. To
turn ON the filter for voice 1, POKE register 23.
Next change line 30 to show that a high-pass filter will be used (see
the SID register map).
PROGRAMMING SOUND AND MUSIC 199
~
EXAMPLE PROGRAM 5 (EXAMPLE 1 MODIFIED):
start tok64 page200.prg
5 s=54272
10 forl=stos+24:pokel,0:next
15 pokes+22,128:pokes+21,0:pokes+23,1
20 pokes+5,9:pokes+6,0
30 pokes+24,79
40 readhf,lf,dr
50 ifhf<0thenend
60 pokes+1,hf:pokes,lf
70 pokes+4,33
80 fort=1todr:next
90 pokes+4,32:fort=1to50:next
100 goto40
110 data25,177,250,28,214,250
120 data25,177,250,25,177,250
130 data25,177,125,28,214,125
140 data32,94,750,25,177,250
150 data28,214,250,19,63,250
160 data19,63,250,19,63,250
170 data21,154,63,24,63,63
180 data25,177,250,24,63,125
190 data19,63,250,-1,-1,-1
stop tok64
Try RUNning the program now. Notice the lower tones have had their
volume cut down. It makes the overall quality of the note sound tinny.
This is because you are using a high-pass filter which attenuates (cuts
down the level of) frequencies below the specified cutoff frequency.
There are three types of filters in your Commodore computer's SID chip.
We have been using the high-pass filter. It will pass all the frequencies
at or above the cutoff, while attenuating the frequencies below the
cutoff.
|
AMOUNT | +-----
PASSED | /
| /
| /
+------|-------
FREQUENCY
200 PROGRAMMING SOUND AND MUSIC
~
The SID chip also has a low-pass filter. As its name implies, this
filter will pass the frequencies below cutoff and attenuate those above.
|
AMOUNT | -----+
PASSED | \
| \
| \
+------|-------
FREQUENCY
Finally, the chip is equipped with a bandpass filter, which passes a
narrow band of frequencies around the cutoff, and attenuates all others.
|
AMOUNT | +
PASSED | / \
| / \
| / \
+------|-------
FREQUENCY
The high- and low-pass filters can be combined to form a notch reject
filter which passes frequencies away from the cutoff while attenuating
at the cutoff frequency.
|
AMOUNT | --+ +---
PASSED | \ /
| \ /
| +
+------|-------
FREQUENCY
PROGRAMMING SOUND AND MUSIC 201
~
Register 24 determines which type filter you want to use. This is in
addition to register 24's function as the overall volume control. Bit 6
controls the high-pass filter (0 = off, 1 = on), bit 5 is the bandpass
filter, and bit 4 is the low-pass filter. The low 3 bits of the cutoff
frequency are determined by register 21 (Lcf) (Lcf = 0 through 7). While
the 8 bits of the high cutoff frequency are determined by register 22
(Hcf) (Hcf = 0 through 255).
Through careful use of filtering, you can change the harmonic structure
of any waveform to get just the sound you want. In addition, changing the
filtering of a sound as it goes through the ADSR phases of its life can
produce interesting effects.
ADVANCED TECHNIQUES
The SID chip's parameters can be changed dynamically during a note or
sound to create many interesting and fun effects. In order to make this
easy to do, digitized outputs from oscillator three and envelope
generator three are available for you in registers 27 and 28, respec-
tively.
The output of oscillator 3 (register 27) is directly related to the
waveform selected. If you choose the sawtooth waveform of oscillator 3,
this register will present a series of numbers incremented (increased
step by step) from 0 to 255 at a rate determined by the frequency of
oscillator 3. If you choose the triangle waveform, the output will incre-
ment from 0 up to 255, then decrement (decrease step by step) back down
to 0. If you choose the pulse wave, the output will jump back-and-forth
between 0 and 255. Finally, choosing the noise waveform will give you a
series of random numbers. When oscillator 3 is used for modulation, you
usually do NOT want to hear its output. Setting bit 7 of register 24
turns the audio output of voice 3 off. Register 27 always reflects the
changing output of the oscillator and is not affected in any way by the
envelope (ADSR) generator.
202 PROGRAMMING SOUND AND MUSIC
~
Register 25 gives you access to the output of the envelope generator
of oscillator 3. It functions in much the same fashion that the output of
oscillator 3 does. The oscillator must be turned on to produce any output
from this register.
Vibrato (a rapid variation in frequency) can be achieved by adding the
output of oscillator 3 to the frequency of another oscillator. Example
Program 6 illustrates this idea.
EXAMPLE PROGRAM 6:
start tok64 page203.prg
10 s=54272
20 forl=0to24:pokes+l,0:next
30 pokes+3,8
40 pokes+5,41:pokes+6,89
50 pokes+14,117
60 pokes+18,16
70 pokes+24,143
80 readfr,dr
90 iffr=0thenend
100 pokes+4,65
110 fort=1todr*2
120 fq=fr+peek(s+27)/2
130 hf=int(fq/256):lf=lqand255
140 pokes+0,lf:pokes+1,hf
150 next
160 pokes+4,64
170 goto80
500 data4817,2,5103,2,5407,2
510 data8583,4,5407,2,8583,4
520 data5407,4,8583,12,9634,2
530 data10207,2,10814,2,8583,2
540 data9634,4,10814,2,8583,2
550 data8583,12
560 data0,0
stop tok64
PROGRAMMING SOUND AND MUSIC 203
~
LINE-BY-LINE EXPLANATION OF EXAMPLE PROGRAM 6:
+----------+------------------------------------------------------------+
| Lines(s) | Description |
+----------+------------------------------------------------------------+
| 10 | Set S to beginning of sound chip. |
| 20 | Clear all sound chip locations. |
| 30 | Set high pulse width for voice 1. |
| 40 | Set Attack/Decay for voice 1 (A=2, D=9). |
| | Set Sustain/Release for voice 1 (S=5, R=9). |
| 50 | Set low frequency for voice 3. |
| 60 | Set triangle waveform for voice 3. |
| 70 | Set volume 15, turn off audio output of voice 3. |
| 80 | Read frequency and duration of note. |
| 90 | If frequency equals zero, stop. |
| 100 | POKE start pulse waveform control voice 1. |
| 110 | Start timing loop for duration. |
| 120 | Get new frequency using oscillator 3 output. |
| 130 | Get high and low frequency. |
| 140 | POKE high and low frequency for voice 1. |
| 150 | End of timing loop. |
| 160 | POKE stop pulse waveform control voice 1. |
| 170 | Go back for next note. |
| 500-550 | Frequencies and durations for song, |
| 560 | Zeros signal end of song. |
+----------+------------------------------------------------------------+
A wide variety of sound effects can also be achieved using dynamic
effects. For example, the following siren program dynamically changes the
frequency output of oscillator 1 when it's based on the output of
oscillator 3's triangular wave:
204 PROGRAMMING SOUND AND MUSIC
~
EXAMPLE PROGRAM 7:
start tok64 page205.prg
10 s=54272
20 forl=0to24:pokes+l,0:next
30 pokes+14,5
40 pokes+18,16
50 pokes+3,1
60 pokes+24,143
70 pokes+6,240
80 pokes+4,65
90 fr=5389
100 fort=1to200
110 fq=fr+peek(s+27)*3.5
120 hf=int(fq/256):lf=fq-hf*256
130 pokes+0,lf:pokes+1,hf
140 next
150 pokes+24,0
stop tok64
LINE-BY-LINE EXPLANATION OF EXAMPLE PROGRAM 7:
+---------+-------------------------------------------------------------+
| Line(s) | Description |
+---------+-------------------------------------------------------------+
| 10 | Set S to start of sound chip. |
| 20 | Clear sound chip registers. |
| 30 | Set low frequency of voice 3. |
| 40 | Set triangular waveform voice 3. |
| 50 | Set high pulse width for voice 1. |
| 60 | Set volume 15, turn off audio output of voice 3. |
| 70 | Set Sustain/Release for voice I (S=15, R=0). |
| 80 | POKE start pulse waveform control voice 1. |
| 90 | Set lowest frequency for siren. |
| 100 | Begin timing loop. |
| 110 | Get new frequency using output of oscillator 3. |
| 120 | Get high and low frequencies. |
| 130 | POKE high.and low frequencies for voice 1. |
| 140 | End timing loop. |
| 150 | Turn off volume. |
+---------+-------------------------------------------------------------+
PROGRAMMING SOUND AND MUSIC 205
~
The noise waveform can be used to provide a wide range of sound
effects. This example mimics a hand clap using a filtered noise waveform:
EXAMPLE PROGRAM 8:
start tok64 page206.prg
10 s=54272
20 forl=0to24:pokes+l,0:next
30 pokes+0,240:pokes+1,33
40 pokes+5,8
50 pokes+22,104
60 pokes+23,1
70 pokes+24,79
80 forn=1to15
90 pokes+4,129
100 fort=1to250:next:pokes+4,128
110 fort=1to30:next:next
120 pokes+24,0
stop tok64
LINE-BY-LINE EXPLANATION OF EXAMPLE PROGRAM 8:
+---------+-------------------------------------------------------------+
| Line(s) | Description |
+---------+-------------------------------------------------------------+
| 10 | Set S to start of sound chip. |
| 20 | Clear all sound chip registers. |
| 30 | Set high and low frequencies for voice 1. |
| 40 | Set Attack/Decay for voice I (A=0, D=8). |
| 50 | Set high cutoff frequency for filter. |
| 60 | Turn on filter for voice 1. |
| 70 | Set volume 15, high-pass filter. |
| 80 | Count 15 claps. |
| 90 | Set start noise waveform control. |
| 100 | Wait, then set stop noise waveform control. |
| 110 | Wait, then start next clap- |
| 120 | Turn off volume. |
+---------+-------------------------------------------------------------+
206 PROGRAMMING SOUND AND MUSIC
~
SYNCHRONIZATION AND RING MODULATION
The 6581 SID chip lets you create more complex harmonic structures
through synchronization or ring modulation of two voices.
The process of synchronization is basically a logical ANDing of two
wave forms. When either is zero, the output is zero. The following
example uses this process to create an imitation of a mosquito:
EXAMPLE PROGRAM 9:
start tok64 page207.prg
10 s=54272
20 forl=0to24:pokes+l,0:next
30 pokes+1,100
40 pokes+5,219
50 pokes+15,28
60 pokes+24,15
70 pokes+4,19
80 fort=1to5000:next
90 pokes+4,18
100 fort=1to1000:next:pokes+24,0
stop tok64
LINE-BY-LINE EXPLANATION OF EXAMPLE PROGRAM 9:
+---------+-------------------------------------------------------------+
| Line(s) | Description |
+---------+-------------------------------------------------------------+
| 10 | Set S to start of sound chip. |
| 20 | Clear sound chip registers. |
| 30 | Set high frequency voice 1. |
| 40 | Set Attack/Decay for voice 1 (A=13, D=11). |
| 50 | Set high frequency voice 3. |
| 60 | Set volume 15. |
| 70 | Set start triangle, sync waveform control for voice 1. |
| 80 | Timing loop. |
| 90 | Set stop triangle, sync waveform control for voice 1. |
| 100 | Wait, then turn off volume. |
+-----------------------------------------------------------------------+
The synchronization feature is enabled (turned on) in line 70, where
bits 0, 1, and 4 of register 4 are set. Bit 1 enables the syncing
function between voice 1 and voice 3. Bits 0 and 4 have their usual
functions of gating voice 1 and setting the triangular waveform.
PROGRAMMING SOUND AND MUSIC 207
~
Ring modulation (accomplished for voice 1 by setting bit 3 of register
4 in line 70 of the program below) replaces the triangular output of
oscillator I with a "ring modulated" combination of oscillators 1 and 3.
This produces non-harmonic overtone structures for use in mimicking bell
or gong sounds. This program produces a clock chime imitation:
EXAMPLE PROGRAM 10:
start tok64 page208.prg
10 s=54272
20 forl=0to24:pokes+l,0:next
30 pokes+1,130
40 pokes+5,9
50 pokes+15,30
60 pokes+24,15
70 forl=1to12:pokes+4,21
80 fort=1to1000:next:pokes+4,20
90 fort=1to1000:next:next
stop tok64
LINE-BY-LINE EXPLANATION OF EXAMPLE PROGRAM 10:
+---------+-------------------------------------------------------------+
| Line(s) | Description |
+---------+-------------------------------------------------------------+
| 10 | Set S to start of sound chip. |
| 20 | Clear sound chip registers. |
| 30 | Set high frequency for voice 1. |
| 40 | Set Attack/Decay for voice 1 (A=0, D=9). |
| 50 | Set high frequency for voice 3. |
| 60 | Set volume 15. |
| 70 | Count number of clings, set start triangle, ring mod |
| | waveform control voice 1. |
| 80 | Timing loop, set stop triangle, ring mod. |
| 90 | Timing loop, next ding. |
+---------+-------------------------------------------------------------+
The effects available through the use of the parameters of your
Commodore 64's SID chip are numerous and varied. Only through ex-
perimentation on your own will you fully appreciate the capabilities of
your machine. The examples in this section of the Programmer's Reference
Guide merely scratch the surface.
Watch for the book MAKING MUSIC ON YOUR COMMODORE COMPUTER for
everything from simple fun and games to professional-type musical
instruction.
208 PROGRAMMING SOUND AND MUSIC
~
CHAPTER 5
BASIC TO
MACHINE
LANGUAGE
o What Is Machine Language?
o How Do You Write Machine
Language Programs?
o Hexadecimal Notation
o Addressing Modes
o Indexing
o Subroutines
o Useful Tips for the Beginner
o Approaching a Large Task
o MCS6510 Microprocessor
Instruction Set
o Memory Management on the
Commodore 64
o The KERNAL
o KERNAL Power-Up Activities
o Using Machine Language From
BASIC
o Commodore 64 Memory Map
209
~
WHAT IS MACHINE LANGUAGE?
At the heart of every microcomputer, is a central microprocessor. It's
a very special microchip which is the "brain" of the computer. The
Commodore 64 is no exception. Every microprocessor understands its own
language of instructions. These instructions are called machine language
instructions. To put it more precisely, machine language is the ONLY
programming language that your Commodore 64 understands. It is the NATIVE
language of the machine.
If machine language is the only language that the Commodore 64
understands, then how does it understand the CBM BASIC programming
language? CBM BASIC is NOT the machine language of the Commodore 64.
What, then, makes the Commodore 64 understand CBM BASIC instructions like
PRINT and GOTO?
To answer this question, you must first see what happens inside your
Commodore 64. Apart from the microprocessor which is the brain of the
Commodore 64, there is a machine language program which is stored in a
special type of memory so that it can't be changed. And, more impor-
tantly, it does not disappear when the Commodore 64 is turned off, unlike
a program that you may have written. This machine language program is
called the OPERATING SYSTEM of the Commodore 64. Your Commodore 64 knows
what to do when it's turned on because its OPERATING SYSTEM (program) is
automatically "RUN."
210 BASIC TO MACHINE LANGUAGE
~
The OPERATING SYSTEM is in charge of "organizing" all the memory in
your machine for various tasks. It also looks at what characters you type
on the keyboard and puts them onto the screen, plus a whole number of
other functions. The OPERATING SYSTEM can be thought of as the
"intelligence and personality" of the Commodore 64 (or any computer for
that matter). So when you turn on your Commodore 64, the OPERATING SYSTEM
takes control of your machine, and after it has done its housework, it
then says:
READY.
The OPERATING SYSTEM of the Commodore 64 then allows you to type on the
keyboard, and use the built-in SCREEN EDITOR on the Commodore 64. The
SCREEN EDITOR allows you to move the cursor, DELete, INSert, etc., and
is, in fact, only one part of the operating system that is built in for
your convenience.
All of the commands that are available in CBM BASIC are simply
recognized by another huge machine language program built into your
Commodore 64. This huge program "RUNS" the appropriate piece of machine
language depending on which CBM BASIC command is being executed. This
program is called the BASIC INTERPRETER, because it interprets each
command, one by one, unless it encounters a command it does not
understand, and then the familiar message appears:
?SYNTAX ERROR
READY.
WHAT DOES MACHINE CODE LOOK LIKE?
You should be familiar with the PEEK and POKE commands in the CBM BASIC
language for changing memory locations. You've probably used them for
graphics on the screen, and for sound effects. Each memory location has
its own number which identifies it. This number is known as the "address"
of a memory location. If you imagine the memory in the Commodore 64 as a
street of buildings, then the number on each door is, of course, the
address. Now let's look at which parts of the street are used for what
purposes.
BASIC TO MACHINE LANGUAGE 211
~
SIMPLE MEMORY MAP OF THE COMMODORE 64
+-------------+---------------------------------------------------------+
| ADDRESS | DESCRIPTION |
+-------------+---------------------------------------------------------+
| | |
| 0 & 1 | -6510 Registers. |
| | |
| 2 | -Start of memory. |
| | |
| 2-1023 | -Memory used by the operating system. |
| | |
| 1024-2039 | -Screen memory. |
| | |
| 2040-2047 | -SPRITE pointers. |
| | |
| 2048-40959 | -This is YOUR memory. This is where your BASIC or |
| | machine language programs, or both, are stored. |
| | |
| 40960-49151 | -8K CBM BASIC Interpreter. |
| | |
| 49152-53247 | -Special programs RAM area. |
| | |
| 53248-53294 | -VIC-II. |
| | |
| 54272-55295 | -SID Registers. |
| | |
| 55296-56296 | -Color RAM. |
| | |
| 56320-57343 | -I/O Registers. (6526's) |
| | |
| 57344-65535 | -8K CBM KERNAL Operating System. |
| | |
+-------------+---------------------------------------------------------+
212 BASIC TO MACHINE LANGUAGE
~
If you don't understand what the description of each part of memory
means right now, this will become clear from other parts of this manual.
Machine language programs consist of instructions which may or may not
have operands (parameters) associated with them. Each instruction takes
up one memory location, and any operand is contained in one or two
locations following the instruction.
In your BASIC programs, words like PRINT and GOTO do, in fact, only
take up one memory location, rather than one for each character of the
word. The contents of the location that represents a particular BASIC
keyword is called a token. In machine language, there are different
tokens for different instructions, which also take up just one byte (mem-
ory location=byte).
Machine language instructions are very simple. Therefore, each indi-
vidual instruction cannot achieve a great deal. Machine language in-
structions either change the contents of a memory location, or change one
of the internal registers (special storage locations) inside the micro-
processor. The internal registers form the very basis of machine lan-
guage.
THE REGISTERS INSIDE THE 6510 MICROPROCESSOR
THE ACCUMULATOR
This is THE most important register in the microprocessor. Various ma-
chine language instructions allow you to copy the contents of a memory
location into the accumulator, copy the contents of the accumulator into
a memory location, modify the contents of the accumulator or some other
register directly, without affecting any memory. And the accumulator is
the only register that has instructions for performing math.
THE X INDEX REGISTER
This is a very important register. There are instructions for nearly
all of the transformations you can make to the accumulator. But there are
other instructions for things that only the X register can do. Various
machine language instructions allow you to copy the contents of a memory
location into the X register, copy the contents of the X register into a
memory location, and modify the contents of the X, or some other register
directly.
BASIC TO MACHINE LANGUAGE 213
~
THE Y INDEX REGISTER
This is a very important register. There are instructions for nearly
all of the transformations you can make to the accumulator, and the X
register. But there are other instructions for things that only the Y
register can do. Various machine language instructions allow you to copy
the contents of a memory location into the Y register, copy the contents
of the Y register into a memory location, and modify the contents of the
Y, or some other register directly.
THE STATUS REGISTER
This register consists of eight "flags" (a flag = something that indi-
cates whether something has, or has not occurred).
THE PROGRAM COUNTER
This contains the address of the current machine language instruction
being executed. Since the operating system is always "RUN"ning in the
Commodore 64 (or, for that matter, any computer), the program counter is
always changing. It could only be stopped by halting the microprocessor
in some way.
THE STACK POINTER
This register contains the location of the first empty place on the
stack. The stack is used for temporary storage by machine language pro-
grams, and by the computer.
THE INPUT/OUTPUT PORT
This register appears at memory locations 0 (for the DATA DIRECTION
REGISTER) and 1 (for the actual PORT). It is an 8-bit input/output port.
On the Commodore 64 this register is used for memory management, to
allow the chip to control more than 64K of RAM and ROM memory.
The details of these registers are not given here. They are explained
as the principles needed to explain them are explained.
HOW DO YOU WRITE MACHINE LANGUAGE PROGRAMS?
Since machine language programs reside in memory, and there is no
facility in your Commodore 64 for writing and editing machine language
214 BASIC TO MACHINE LANGUAGE
~
programs, you must use either a program to do this, or write for yourself
a BASIC program that "allows" you to write machine language.
The most common methods used to write machine language programs are
assembler programs. These packages allow you to write machine language
instructions in a standardized mnemonic format, which makes the machine
language program a lot more readable than a stream of numbers! Let's
review: A program that allows you to write machine language programs in
mnemonic format is called an assembler. Incidentally, a program that
displays a machine language program in mnemonic format is called a
disassembler. Available for your Commodore 64 is a machine language
monitor cartridge (with assembler/disassembler, etc.) made by Commodore:
64MON
The 64MON cartridge available from your local dealer, is a program that
allows you to escape from the world of CBM BASIC, into the land of
machine language. It can display the contents of the internal registers
in the 6510 microprocessor, and it allows you to display portions of mem-
ory, and change them on the screen, using the screen editor. It also has
a built-in assembler and disassembler, as well as many other features
that allow you to write and edit machine language programs easily. You
don't HAVE to use an assembler to write machine language, but the task is
considerably easier with it. If you wish to write machine language
programs, it is strongly suggested that you purchase an assembler of some
sort. Without an assembler you will probably have to "POKE" the machine
language program into memory, which is totally unadvisable. This manual
will give its examples in the format that 64MON uses, from now on. Nearly
all assembler formats are the same, therefore the machine language
examples shown will almost certainly be compatible with any assembler.
But before explaining any of the other features of 64MON, the hexadecimal
numbering system must be explained.
HEXADECIMAL NOTATION
Hexadecimal notation is used by most machine language programmers when
they talk about a number or address in a machine language program.
Some assemblers let you refer to addresses and numbers in decimal
(base 10), binary (base 2), or even octal (base 8) as well as hexadecimal
BASIC TO MACHINE LANGUAGE 215
~
(base 16) (or just "hex" as most people say). These assemblers do the
conversions for you.
Hexadecimal probably seems a little hard to grasp at first, but like
most things, it won't take long to master with practice.
By looking at decimal (base 10) numbers, you can see that each digit
fails somewhere in the range between zero and a number equal to the base
less one (e.g., 9). THIS IS TRUE OF ALL NUMBER BASES. Binary (base 2)
numbers have digits ranging from zero to one (which is one less than the
base). Similarly, hexadecimal numbers should have digits ranging from
zero to fifteen, but we do not have any single digit figures for the
numbers ten to fifteen, so the first six letters of the alphabet are used
instead:
+---------+-------------+----------+
| DECIMAL | HEXADECIMAL | BINARY |
+---------+-------------+----------+
| 0 | 0 | 00000000 |
| 1 | 1 | 00000001 |
| 2 | 2 | 00000010 |
| 3 | 3 | 00000011 |
| 4 | 4 | 00000100 |
| 5 | 5 | 00000101 |
| 6 | 6 | 00000110 |
| 7 | 7 | 00000111 |
| 8 | 8 | 00001000 |
| 9 | 9 | 00001001 |
| 10 | A | 00001010 |
| 11 | B | 00001011 |
| 12 | C | 00001100 |
| 13 | D | 00001101 |
| 14 | E | 00001110 |
| 15 | F | 00001111 |
| 16 | 10 | 00010000 |
+---------+-------------+----------+
216 BASIC TO MACHINE LANGUAGE
~
Let's look at it another way; here's an example of how a base 10
(decimal number) is constructed:
Base raised by
increasing powers:... 10^3 10^2 10^1 10^0
---------------------
Equals:.............. 1000 100 10 1
---------------------
Consider 4569 (base 10) 4 5 6 9 = (4*1000)+(5*100)+(6*10)+9
Now look at an example of how a base 16 (hexadecimal number) is
constructed:
Base raised by
increasing powers:... 16^3 16^2 16^1 16^0
---------------------
Equals:.............. 4096 256 16 1
---------------------
Consider 11D9 (base 16) 1 1 D 9 = 1*4096+1*256+13*16+9
Therefore, 4569 (base 10) = 11D9 (base 16)
The range for addressable memory locations is 0-65535 (as was stated
earlier). This range is therefore 0-FFFF in hexadecimal notation.
Usually hexadecimal numbers are prefixed with a dollar sign ($). This
is to distinguish them from decimal numbers. Let's look at some "hex"
numbers, using 64MON, by displaying the contents of some memory by
typing:
SYS 8*4096 (or SYS 12*4096)
B*
PC SR AC XR YR SP
.;0401 32 04 5E 00 F6 (these may be different)
Then if you type in:
.M 0000 0020 (and press <RETURN>).
you will see rows of 9 hex numbers. The first 4-digit number is the ad-
dress of the first byte of memory being shown in that row, and the other
eight numbers are the actual contents of the memory locations beginning
at that start address.
BASIC TO MACHINE LANGUAGE 217
~
You should really try to learn to "think" in hexadecimal. It's not too
difficult, because you don't have to think about converting it back into
decimal. For example, if you said that a particular value is stored at
$14ED instead of 5357, it shouldn't make any difference.
YOUR FIRST MACHINE LANGUAGE INSTRUCTION
LDA - LOAD THE ACCUMULATOR
In 6510 assembly language, mnemonics are always three characters. LDA
represents "load accumulator with...", and what the accumulator should be
loaded with is decided by the parameter(s) associated with that
instruction. The assembler knows which token is represented by each
mnemonic, and when it "assembles" an instruction, it simply puts into
memory (at whatever address has been specified), the token, and what
parameters, are given. Some assemblers give error messages, or warnings
when you try to assemble something that either the assembler, or the 6510
microprocessor, cannot do.
If you put a "#" symbol in front of the parameter associated with the
instruction, this means that you want the register specified in the
instruction to be loaded with the "value" after the "#". For example:
LDA #$05 <----[ $=HEX ]
This instruction will put $05 (decimal 5) into the accumulator register.
The assembler will put into the specified address for this instruction,
$A9 (which is the token for this particular instruction, in this mode),
and it will put $05 into the next location after the location containing
the instruction ($A9).
If the parameter to be used by an instruction has "#" before it; i.e.,
the parameter is a "value," rather than the contents of a memory loca-
tion, or another register, the instruction is said to be in the
"immediate" mode. To put this into perspective, let's compare this with
another mode:
If you want to put the contents of memory location $102E into the
accumulator, you're using the "absolute" mode of instruction:
LDA $102E
The assembler can distinguish between the two different modes because the
latter does not have a "#" before the parameter. The 6510 microprocessor
218 BASIC TO MACHINE LANGUAGE
~
can distinguish between the immediate mode, and the absolute mode of the
LDA instruction, because they have slightly different tokens. LDA
(immediate) has $A9 as its token, and LDA (absolute), has $AD as its
token.
The mnemonic representing an instruction usually implies what it does.
For instance, if we consider another instruction, LDX, what do you think
this does?
If you said "load the X register with...", go to the top of the class.
If you didn't, then don't worry, learning machine language does take
patience, and cannot be learned in a day.
The various internal registers can be thought of as special memory
locations, because they too can hold one byte of information. It is not
necessary for us to explain the binary numbering system (base 2) since it
follows the same rules as outlined for hexadecimal and decimal outlined
previously, but one "bit" is one binary digit and eight bits make up one
byte! This means that the maximum number that can be contained in a
byte is the largest number that an eight digit binary number can be. This
number is 11111111 (binary), which equals $FF (hexadecimal), which equals
255 (decimal). You have probably wondered why only numbers from zero to
255 could be put into a memory location. If you try POKE 7680,260 (which
is a BASIC statement that "says": "Put the number two hundred and sixty,
into memory location seven thousand, six hundred and eighty", the BASIC
interpreter knows that only numbers 0 - 255 can be put in a memory
location, and your Commodore 64 will reply with:
?ILLEGAL QUANTITY ERROR
READY.
If the limit of one byte is $FF (hex), how is the address parameter in
the absolute instruction "LDA $102E" expressed in memory? It's expressed
in two bytes (it won't fit into one, of course). The lower (rightmost)
two digits of the hexadecimal address form the "low byte" of the address,
and the upper (leftmost) two digits form the "high byte."
The 6510 requires any address to be specified with its low byte first,
and then the high byte. This means that the instruction "LDA $102E" is
represented in memory by the three consecutive values:
$AD, $2E, $10
Now all you need to know is one more instruction and then you can write
your first program. That instruction is BRK. For a full explanation of
BASIC TO MACHINE LANGUAGE 219
~
this I instruction, refer to M.O.S. 6502 Programming Manual. But right
now, you can think of it as the END instruction in machine language.
If we write a program with 64MON and put the BRK instruction at the
end, then when the program is executed, it will return to 64MON when it
is finished. This might not happen if there is a mistake in your program,
or the BRK instruction is never reached (just like an END statement in
BASIC may never get executed). This means that if the Commodore 64 didn't
have a STOP key, you wouldn't be able to abort your BASIC programs!
WRITING YOUR FIRST PROGRAM
If you've used the POKE statement in BASIC to put characters onto the
screen, you're aware that the character codes for POKEing are different
from CBM ASCII character values. For example, if you enter:
PRINT ASC("A") (and press <RETURN> )
the Commodore 64 will respond with:
65
READY.
However, to put an "A" onto the screen by POKEing, the code is 1, enter:
<SHIFT+CLR/HOME> to clear the screen
POKE 1024,1:POKE 55296,14 (and <RETURN> (1024 is the start of screen
memory)
The "P" in the POKE statement should now be an "A."
Now let's try this in machine language. Type the following in 64MON:
(Your cursor should be flashing alongside a "." right now.)
.A 1400 LDA#$01 (and press <RETURN>)
220 BASIC TO MACHINE LANGUAGE
~
The Commodore 64 will prompt you with:
.A 1400 A9 01 LDA #$01
.A 1402
Type:
.A 1402 STA $0400
(The STA instruction stores the contents of the accumulator in a
specified memory location.)
The Commodore 64 will prompt you with:
.A 1405
Now type in:
.A 1405 LDA #$0E
.A 1407 STA $D800
.A 140A BRK
Clear the screen, and type:
G 1400
The G should turn into an "A" if you've done everything correctly. You
have now written your first machine language program. Its purpose is to
store one character ("A") at the first location in the screen memory.
Having achieved this, we must now explore some of the other instructions,
and principles.
ADDRESSING MODES
ZERO PAGE
As shown earlier, absolute addresses are expressed in terms of a high
and a low order byte. The high order byte is often referred to as the
page of memory. For example, the address $1637 is in page $16 (22), and
$0277 is in page $02 (2). There is, however, a special mode of addressing
known as zero page addressing and is, as the name implies, associated
BASIC TO MACHINE LANGUAGE 221
~
with the addressing of memory locations in page zero. These addresses,
therefore, ALWAYS have a high order byte of zero. The zero page mode of
addressing only expects one byte to describe the address, rather than two
when using an absolute address. The zero page addressing mode tells the
microprocessor to assume that the high order address is zero. Therefore
zero page addressing can reference memory locations whose addresses are
between $0000 and $00FF. This may not seem too important at the moment,
but you'll need the principles of zero page addressing soon.
THE STACK
The 6510 microprocessor has what is known as a stack. This is used by
both the programmer and the microprocessor to temporarily remember
things, and to remember, for example, an order of events. The GOSUB
statement in BASIC, which allows the programmer to call a subroutine,
must remember where it is being called from, so that when the RETURN
statement is executed in the subroutine, the BASIC interpreter "knows"
where to go back to continue executing. When a GOSUB statement is
encountered in a program by the BASIC interpreter, the BASIC interpreter
"pushes" its current position onto the stack before going to do the
subroutine, and when a RETURN is executed, the interpreter "pulls" off
the stack the information that tells it where it was before the
subroutine call was made. The interpreter uses instructions like PHA,
which pushes the contents of the accumulator onto the stack, and PLA (the
reverse) which pulls a value off the stack and into the accumulator. The
status register can also be pushed and pulled with the PHP and PLP,
respectively.
The stack is 256 bytes long, and is located in page one of memory. It
is therefore from $01 00 to $01 FF. It is organized backwards in memory.
In other words, the first position in the stack is at $01 FF, and the
last is at $0100. Another register in the 651 0 microprocessor is called
the stack pointer, and it always points to the next available location in
the stack. When something is pushed onto the stack, it is placed where
the stack pointer points to, and the stack pointer is moved down to the
next position (decremented). When something is pulled off the stack, the
stack pointer is incremented, and the byte pointed to by the stack
pointer is placed into the specified register.
222 BASIC TO MACHINE LANGUAGE
~
Up to this point, we have covered immediate, zero page, and absolute
mode instructions. We have also covered, but have not really talked
about, the "implied" mode. The implied mode means that information is
implied by an instruction itself. In other words, what registers, flags,
and memory the instruction is referring to. The examples we have seen are
PHA, PLA, PHP, and PLP, which refer to stack processing and the
accumulator and status registers, respectively.
+-----------------------------------------------------------------------+
| NOTE: The X register will be referred to as X from now on, and |
| similarly A (accumulator), Y (Y index register), S (stack pointer), |
| and P (processor status). |
+-----------------------------------------------------------------------+
INDEXING
Indexing plays an extremely important part in the running of the 6510
microprocessor. It can be defined as "creating an actual address from a
base address plus the contents of either the X or Y index registers."
For example, if X contains $05, and the microprocessor executes an LDA
instruction in the "absolute X indexed mode" with base address (e.g.,
$9000), then the actual location that is loaded into the A register is
$9000 + $05 = $9005. The mnemonic format of an absolute indexed
instruction is the same as an absolute instruction except a ",X" or ",Y"
denoting the index is added to the address.
EXAMPLE:
LDA $9000,X
There are absolute indexed, zero page indexed, indirect indexed, and
indexed indirect modes of addressing available on the 6510
microprocessor.
INDIRECT INDEXED
This only allows usage of the Y register as the index. The actual ad-
dress can only be in zero page, and the mode of instruction is called
indirect because the zero page address specified in the instruction con-
tains the low byte of the actual address, and the next byte to it
contains the high order byte.
BASIC TO MACHINE LANGUAGE 223
~
EXAMPLE:
Let us suppose that location $02 contains $45, and location $03 con-
tains $1E. If the instruction to load the accumulator in the indirect
indexed mode is executed and the specified zero page address is $02, then
the actual address will be:
Low order = contents of $02
High order = contents of $03
Y register = $00
Thus the actual address = $1E45 + Y = $1E45.
The title of this mode does in fact imply an indirect principle,
although this may be difficult to grasp at first sight. Let's look at it
another way:
"I am going to deliver this letter to the post office at address $02,
MEMORY ST., and the address on the letter is $05 houses past $1600,
MEMORY street." This is equivalent to the code:
LDA #$00 - load low order actual base address
STA $02 - set the low byte of the indirect address
LDA #$16 - load high order indirect address
STA $03 - set the high byte of the indirect address
LDY #$05 - set the indirect index (Y)
LDA ($02),Y - load indirectly indexed by Y
INDEXED INDIRECT
Indexed indirect only allows usage of the X register as the index. This
is the some as indirect indexed, except it is the zero page address of
the pointer that is indexed, rather than the actual base address.
Therefore, the actual base address IS the actual address because the
index has already been used for the indirect. Index indirect would also
be used if a table of indirect pointers were located in zero page memory,
and the X register could then specify which indirect pointer to use.
224 BASIC TO MACHINE LANGUAGE
~
EXAMPLE:
Let us suppose that location $02 contains $45, and location $03 con-
tains $10. If the instruction to load the accumulator in the indexed
indirect mode is executed and the specified zero page address is $02,
then the actual address will be:
Low order = contents of ($02+X)
High order = contents of ($03+X)
X register = $00
Thus the actual pointer is in = $02 + X = $02.
Therefore, the actual address is the indirect address contained in $02
which is again $1045.
The title of this mode does in fact imply the principle, although it
may be difficult to grasp at first sight. Look at it this way:
"I am going to deliver this letter to the fourth post office at address
$01,MEMORY ST., and the address on the letter will then be delivered to
$1600, MEMORY street." This is equivalent to the code:
LDA #$00 - load low order actual base address
STA $06 - set the low byte of the indirect address
LDA #$16 - load high order indirect address
STA $07 - set the high byte of the indirect address
LDX #$05 - set the indirect index (X)
LDA ($02,X) - load indirectly indexed by X
+-----------------------------------------------------------------------+
| NOTE: Of the two indirect methods of addressing, the first (indirect |
| indexed) is far more widely used. |
+-----------------------------------------------------------------------+
BASIC TO MACHINE LANGUAGE 225
~
BRANCHES AND TESTING
Another very important principle in machine language is the ability to
test, and detect certain conditions, in a similar fashion to the "IF...
THEN, IF... GOTO" structure in CBM BASIC.
The various flags in the status register are affected by different in-
structions in different ways. For example, there is a flag that is set
when an instruction has caused a zero result, and is reset when a result
is not zero. The instruction:
LDA #$00
will cause the zero result flag to be set, because the instruction has
resulted in the accumulator containing a zero.
There are a set of instructions that will, given a particular
condition, branch to another part of the program. An example of a branch
instruction is BEQ, which means Branch if result EQual to zero. The
branch instructions branch if the condition is true, and if not, the
program continues onto the next instruction, as if nothing had occurred.
The branch instructions branch not by the result of the previous
instructions), but by internally examining the status register. As was
just mentioned, there is a zero result flag in the status register. The
BEQ instruction branches if the zero result flag (known as Z) is set.
Every branch instruction has an opposite branch instruction. The BEQ
instruction has an opposite instruction BNE, which means Branch on result
Not Equal to zero (i.e., Z not set).
The index registers have a number of associated instructions which
modify their contents. For example, the INX instruction INcrements the X
index register. If the X register contained $FF before it was incremented
(the maximum number the X register can contain), it will "wrap around"
back to zero. If you wanted a program to continue to do something until
you had performed the increment of the X index that pushed it around to
zero, you could use the BNE instruction to continue "looping" around,
until X became zero.
The reverse of INX, is DEX, which is DEcrement the X index register. If
the X index register is zero, DEX wraps around to $FF. Similarly, there
are INY and DEY for the Y index register.
226 BASIC TO MACHINE LANGUAGE
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But what if a program didn't want to wait until X or Y had reached (or
not reached) zero? Well there are comparison instructions, CPX and CPY,
which allow the machine language programmer to test the index registers
with specific values, or even the contents of memory locations. If you
wanted to see if the X register contained $40, you would use the
instruction:
CPX #$40 - compare X with the "value" $40.
BEQ - branch to somewhere else in the
(some other program, if this condition is "true."
part of the
program)
The compare, and branch instructions play a major part in any machine
language program.
The operand specified in a branch instruction when using 64MON is the
address of the part of the program that the branch goes to when the
proper conditions are met. However, the operand is only an offset, which
gets you from where the program currently is to the address specified.
This offset is just one byte, and therefore the range that a branch
instruction can branch to is limited. It can branch from 128 bytes back-
ward, to 127 bytes forward.
+-----------------------------------------------------------------------+
| NOTE: This is a total range of 255 bytes which is, of course, the |
| maximum range of values one byte can contain. |
+-----------------------------------------------------------------------+
64MON will tell you if you "branch out of range" by refusing to "as-
semble" that particular instruction. But don't worry about that now be-
cause it's unlikely that you will have such branches for quite a while.
The branch is a "quick" instruction by machine language standards because
of the "offset" principle as opposed to an absolute address. 64MON allows
you to type in an absolute address, and it calculates the correct offset.
This is just one of the "comforts" of using an assembler.
+-----------------------------------------------------------------------+
| NOTE: It is NOT possible to cover every single branch instruction. For|
| further information, refer to the Bibliography section in Appendix F. |
+-----------------------------------------------------------------------+
BASIC TO MACHINE LANGUAGE 227
~
SUBROUTINES
In machine language (in the same way as using BASIC), you can call
subroutines. The instruction to call a subroutine is JSR (Jump to Sub-
Routine), followed by the specified absolute address.
Incorporated in the operating system, there is a machine language
subroutine that will PRINT a character to the screen. The CBM ASCII code
of the character should be in the accumulator before calling the
subroutine. The address of this subroutine is $FFD2.
Therefore, to print "Hi" to the screen, the following program should be
entered:
.A 1400 LDA #$48 - load the CBM ASCII code of "H"
.A 1402 JSR $FFD2 - print it
.A 1405 LDA #$49 - load the CBM ASCII code of "I"
.A 1407 JSR $FFD2 - print that too
.A 140A LDA #$0D - print a carriage return as well
.A 140C JSR $FFD2
.A 140F BRK - return to 64MON
.G 1400 - will print "HI" and return to 64MON
The "PRINT a character" routine we have just used is part of the KERNAL
jump table. The instruction similar to GOTO in BASIC is JMP, which means
JUMP to the specified absolute address. The KERNAL is a long list of
"standardized" subroutines that control ALL input and output of the
Commodore 64. Each entry in the KERNAL JMPs to a subroutine in the
operating system. This "jump table" is found between memory locations
$FF84 to $FFF5 in the operating system. A full explanation of the KERNAL
is available in the "KERNAL Reference Section" of this manual. However,
certain routines are used here to show how easy and effective the KERNAL
is.
Let's now use the new principles you've just learned in another pro-
gram. It will help you to put the instructions into context:
228 BASIC TO MACHINE LANGUAGE
~
This program. will display the alphabet using a KERNAL routine. The
only new instruction introduced here is TXA Transfer the contents of the
X index register, into the Accumulator.
.A 1400 LDX #$41 - X = CBM ASCII of "A"
.A 1402 TXA - A = X
.A 1403 JSR $FFD2 - print character
.A 1406 INX - bump count
.A 1407 CPX #$5B - have we gone past "Z"?
.A 1409 BNE $1402 - no, go back and do more
.A 140B BRK - yes, return to 64MON
To see the Commodore 64 print the alphabet, type the familiar command:
.G 1400
The comments that are beside the program, explain the program flow and
logic. If you are writing a program, write it on paper first, and then
test it in small parts if possible.
USEFUL TIPS FOR THE BEGINNER
One of the best ways to learn machine language is to look at other
peoples' machine language programs. These are published all the time in
magazines and newsletters. Look at them even if the article is for a
different computer, which also uses the 6510 (or 6502) microprocessor.
You should make sure that you thoroughly understand the code that you
look at. This will require perseveres I ce, especially when you see a new
technique that you have never come across before. This can be infuriat-
ing, but if patience prevails, you will be the victor.
Having looked at other machine language programs, you MUST write your
own. These may be utilities for your BASIC programs, or they may be an
all machine language program.
BASIC TO MACHINE LANGUAGE 229
~
You should also use the utilities that are available, either IN your
computer, or in a program, that aid you in writing, editing, or tracking
down errors in a machine language program. An example would be the
KERNAL, which allows you to check the keyboard, print text, control
peripheral devices like disk drives, printers, modems, etc., manage
memory and the screen. It is extremely powerful and it is advised
strongly that it is used (refer to KERNAL section, Page 268).
Advantages of writing programs in machine language:
1. Speed - Machine language is hundreds, and in some cases thousands of
times faster than a high level language such as BASIC.
2. Tightness - A machine language program can be made totally
"watertight," i.e., the user can be made to do ONLY what the program
allows, and no more. With a high level language, you are relying on
the user not "crashing" the BASIC interpreter by entering, for
example, a zero which later causes a:
?DIVISION BY ZERO ERROR IN LINE 830
READY.
In essence, the computer can only be maximized by the machine language
programmer.
APPROACHING A LARGE TASK
When approaching a large task in machine language, a certain amount of
subconscious thought has usually taken place. You think about how certain
processes are carried out in machine language. When the task is started,
it is usually a good idea to write it out on paper. Use block diagrams of
memory usage, functional modules of code required, and a program flow.
Let's say that you wanted to write a roulette game in machine language.
You could outline it something like this:
230 BASIC TO MACHINE LANGUAGE
~
o Display title
o Ask if player requires instructions
o YES - display them-Go to START
o NO - Go to START
o START Initialize everything
o MAIN display roulette table
o Take in bets
o Spin wheel
o Slow wheel to stop
o Check bets with result
o Inform player
o Player any money left?
o YES - Go to MAIN
o NO - Inform user!, and go to START
This is the main outline. As each module is approached, you can break
it down further. If you look at a large indigestable problem as something
that can be broken down into small enough pieces to be eaten, then you'll
be able to approach something that seems impossible, and have it all fall
into place.
This process only improves with practice, so KEEP TRYING.
BASIC TO MACHINE LANGUAGE 231
~
+------------------------------------------------------------------------
|
| MCS6510 MICROPROCESSOR INSTRUCTION SET - ALPHABETIC SEQUENCE
|
+------------------------------------------------------------------------
|
| ADC Add Memory to Accumulator with Carry
| AND "AND" Memory with Accumulator
| ASL Shift Left One Bit (Memory or Accumulator)
|
| BCC Branch on Carry Clear
| BCS Branch on Carry Set
| BEQ Branch on Result Zero
| BIT Test Bits in Memory with Accumulator
| BMI Branch on Result Minus
| BNE Branch on Result not Zero
| BPL Branch on Result Plus
| BRK Force Break
| BVC Branch on Overflow Clear
| BVS Branch on Overflow Set
|
| CLC Clear Carry Flag
| CLD Clear Decimal Mode
| CLI Clear interrupt Disable Bit
| CLV Clear Overflow Flag
| CMP Compare Memory and Accumulator
| CPX Compare Memory and Index X
| CPY Compare Memory and Index Y
|
| DEC Decrement Memory by One
| DEX Decrement Index X by One
| DEY Decrement Index Y by One
|
| EOR "Exclusive-Or" Memory with Accumulator
|
| INC Increment Memory by One
| INX Increment Index X by One
| INY Increment Index Y by One
|
| JMP Jump to New Location
|
+------------------------------------------------------------------------
232 BASIC TO MACHINE LANGUAGE
~
------------------------------------------------------------------------+
|
MCS6510 MICROPROCESSOR INSTRUCTION SET - ALPHABETIC SEQUENCE |
|
------------------------------------------------------------------------+
|
JSR Jump to New Location Saving Return Address |
|
LDA Load Accumulator with Memory |
LDX Load Index X with Memory |
LDY Load Index Y with Memory |
LSR Shift Right One Bit (Memory or Accumulator) |
|
NOP No Operation |
|
ORA "OR" Memory with Accumulator |
|
PHA Push Accumulator on Stack |
PHP Push Processor Status on Stack |
PLA Pull Accumulator from Stack |
PLP Pull Processor Status from Stack |
|
ROL Rotate One Bit Left (Memory or Accumulator) |
ROR Rotate One Bit Right (Memory or Accumulator) |
RTI Return from Interrupt |
RTS Return from Subroutine |
|
SBC Subtract Memory from Accumulator with Borrow |
SEC Set Carry Flag |
SED Set Decimal Mode |
SEI Set Interrupt Disable Status |
STA Store Accumulator in Memory |
STX Store Index X in Memory |
STY Store Index Y in Memory |
|
TAX Transfer Accumulator to Index X |
TAY Transfer Accumulator to Index Y |
TSX Transfer Stack Pointer to Index X |
TXA Transfer Index X to Accumulator |
TXS Transfer Index X to Stack Pointer |
TYA Transfer Index Y to Accumulator |
------------------------------------------------------------------------+
BASIC TO MACHINE LANGUAGE 233
~
The following notation applies to this summary:
A Accumulator EOR Logical Exclusive Or
X, Y Index Registers fromS Transfer from Stack
M Memory toS Transfer to Stack
P Processor Status Register -> Transfer to
S Stack Pointer <- Transfer from
/ Change V Logical OR
_ No Change PC Program Counter
+ Add PCH Program Counter High
/\ Logical AND PCL Program Counter Low
- Subtract OPER OPERAND
# IMMEDIATE ADDRESSING MODE
Note: At the top of each table is located in parentheses a reference
number (Ref: XX) which directs the user to that Section in the
MCS6500 Microcomputer Family Programming Manual in which the
instruction is defined and discussed.
234 BASIC TO MACHINE LANGUAGE
~
ADC Add memory to accumulator with carry ADC
Operation: A + M + C -> A, C N Z C I D V
/ / / _ _ /
(Ref: 2.2.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | ADC #Oper | 69 | 2 | 2 |
| Zero Page | ADC Oper | 65 | 2 | 3 |
| Zero Page,X | ADC Oper,X | 75 | 2 | 4 |
| Absolute | ADC Oper | 60 | 3 | 4 |
| Absolute,X | ADC Oper,X | 70 | 3 | 4* |
| Absolute,Y | ADC Oper,Y | 79 | 3 | 4* |
| (Indirect,X) | ADC (Oper,X) | 61 | 2 | 6 |
| (Indirect),Y | ADC (Oper),Y | 71 | 2 | 5* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if page boundary is crossed.
AND "AND" memory with accumulator AND
Operation: A /\ M -> A N Z C I D V
/ / _ _ _ _
(Ref: 2.2.3.0)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | AND #Oper | 29 | 2 | 2 |
| Zero Page | AND Oper | 25 | 2 | 3 |
| Zero Page,X | AND Oper,X | 35 | 2 | 4 |
| Absolute | AND Oper | 2D | 3 | 4 |
| Absolute,X | AND Oper,X | 3D | 3 | 4* |
| Absolute,Y | AND Oper,Y | 39 | 3 | 4* |
| (Indirect,X) | AND (Oper,X) | 21 | 2 | 6 |
| (Indirect,Y) | AND (Oper),Y | 31 | 2 | 5 |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if page boundary is crossed.
BASIC TO MACHINE LANGUAGE 235
~
ASL ASL Shift Left One Bit (Memory or Accumulator) ASL
+-+-+-+-+-+-+-+-+
Operation: C <- |7|6|5|4|3|2|1|0| <- 0
+-+-+-+-+-+-+-+-+ N Z C I D V
/ / / _ _ _
(Ref: 10.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Accumulator | ASL A | 0A | 1 | 2 |
| Zero Page | ASL Oper | 06 | 2 | 5 |
| Zero Page,X | ASL Oper,X | 16 | 2 | 6 |
| Absolute | ASL Oper | 0E | 3 | 6 |
| Absolute, X | ASL Oper,X | 1E | 3 | 7 |
+----------------+-----------------------+---------+---------+----------+
BCC BCC Branch on Carry Clear BCC
N Z C I D V
Operation: Branch on C = 0 _ _ _ _ _ _
(Ref: 4.1.1.3)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BCC Oper | 90 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 2 if branch occurs to different page.
BCS BCS Branch on carry set BCS
Operation: Branch on C = 1 N Z C I D V
_ _ _ _ _ _
(Ref: 4.1.1.4)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BCS Oper | B0 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 2 if branch occurs to next page.
236 BASIC TO MACHINE LANGUAGE
~
BEQ BEQ Branch on result zero BEQ
N Z C I D V
Operation: Branch on Z = 1 _ _ _ _ _ _
(Ref: 4.1.1.5)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BEQ Oper | F0 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 2 if branch occurs to next page.
BIT BIT Test bits in memory with accumulator BIT
Operation: A /\ M, M7 -> N, M6 -> V
Bit 6 and 7 are transferred to the status register. N Z C I D V
If the result of A /\ M is zero then Z = 1, otherwise M7/ _ _ _ M6
Z = 0
(Ref: 4.2.1.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Zero Page | BIT Oper | 24 | 2 | 3 |
| Absolute | BIT Oper | 2C | 3 | 4 |
+----------------+-----------------------+---------+---------+----------+
BMI BMI Branch on result minus BMI
Operation: Branch on N = 1 N Z C I D V
_ _ _ _ _ _
(Ref: 4.1.1.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BMI Oper | 30 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 1 if branch occurs to different page.
BASIC TO MACHINE LANGUAGE 237
~
BNE BNE Branch on result not zero BNE
Operation: Branch on Z = 0 N Z C I D V
_ _ _ _ _ _
(Ref: 4.1.1.6)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BMI Oper | D0 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 2 if branch occurs to different page.
BPL BPL Branch on result plus BPL
Operation: Branch on N = 0 N Z C I D V
_ _ _ _ _ _
(Ref: 4.1.1.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BPL Oper | 10 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 2 if branch occurs to different page.
BRK BRK Force Break BRK
Operation: Forced Interrupt PC + 2 toS P toS N Z C I D V
_ _ _ 1 _ _
(Ref: 9.11)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | BRK | 00 | 1 | 7 |
+----------------+-----------------------+---------+---------+----------+
1. A BRK command cannot be masked by setting I.
238 BASIC TO MACHINE LANGUAGE
~
BVC BVC Branch on overflow clear BVC
Operation: Branch on V = 0 N Z C I D V
_ _ _ _ _ _
(Ref: 4.1.1.8)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BVC Oper | 50 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 2 if branch occurs to different page.
BVS BVS Branch on overflow set BVS
Operation: Branch on V = 1 N Z C I D V
_ _ _ _ _ _
(Ref: 4.1.1.7)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BVS Oper | 70 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 2 if branch occurs to different page.
CLC CLC Clear carry flag CLC
Operation: 0 -> C N Z C I D V
_ _ 0 _ _ _
(Ref: 3.0.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | CLC | 18 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
BASIC TO MACHINE LANGUAGE 239
~
CLD CLD Clear decimal mode CLD
Operation: 0 -> D N A C I D V
_ _ _ _ 0 _
(Ref: 3.3.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | CLD | D8 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
CLI CLI Clear interrupt disable bit CLI
Operation: 0 -> I N Z C I D V
_ _ _ 0 _ _
(Ref: 3.2.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | CLI | 58 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
CLV CLV Clear overflow flag CLV
Operation: 0 -> V N Z C I D V
_ _ _ _ _ 0
(Ref: 3.6.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | CLV | B8 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
240 BASIC TO MACHINE LANGUAGE
~
CMP CMP Compare memory and accumulator CMP
Operation: A - M N Z C I D V
/ / / _ _ _
(Ref: 4.2.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | CMP #Oper | C9 | 2 | 2 |
| Zero Page | CMP Oper | C5 | 2 | 3 |
| Zero Page,X | CMP Oper,X | D5 | 2 | 4 |
| Absolute | CMP Oper | CD | 3 | 4 |
| Absolute,X | CMP Oper,X | DD | 3 | 4* |
| Absolute,Y | CMP Oper,Y | D9 | 3 | 4* |
| (Indirect,X) | CMP (Oper,X) | C1 | 2 | 6 |
| (Indirect),Y | CMP (Oper),Y | D1 | 2 | 5* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if page boundary is crossed.
CPX CPX Compare Memory and Index X CPX
N Z C I D V
Operation: X - M / / / _ _ _
(Ref: 7.8)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | CPX *Oper | E0 | 2 | 2 |
| Zero Page | CPX Oper | E4 | 2 | 3 |
| Absolute | CPX Oper | EC | 3 | 4 |
+----------------+-----------------------+---------+---------+----------+
CPY CPY Compare memory and index Y CPY
N Z C I D V
Operation: Y - M / / / _ _ _
(Ref: 7.9)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | CPY *Oper | C0 | 2 | 2 |
| Zero Page | CPY Oper | C4 | 2 | 3 |
| Absolute | CPY Oper | CC | 3 | 4 |
+----------------+-----------------------+---------+---------+----------+
BASIC TO MACHINE LANGUAGE 241
~
DEC DEC Decrement memory by one DEC
Operation: M - 1 -> M N Z C I D V
/ / _ _ _ _
(Ref: 10.7)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Zero Page | DEC Oper | C6 | 2 | 5 |
| Zero Page,X | DEC Oper,X | D6 | 2 | 6 |
| Absolute | DEC Oper | CE | 3 | 6 |
| Absolute,X | DEC Oper,X | DE | 3 | 7 |
+----------------+-----------------------+---------+---------+----------+
DEX DEX Decrement index X by one DEX
Operation: X - 1 -> X N Z C I D V
/ / _ _ _ _
(Ref: 7.6)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | DEX | CA | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
DEY DEY Decrement index Y by one DEY
Operation: X - 1 -> Y N Z C I D V
/ / _ _ _ _
(Ref: 7.7)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | DEY | 88 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
242 BASIC TO MACHINE LANGUAGE
~
EOR EOR "Exclusive-Or" memory with accumulator EOR
Operation: A EOR M -> A N Z C I D V
/ / _ _ _ _
(Ref: 2.2.3.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | EOR #Oper | 49 | 2 | 2 |
| Zero Page | EOR Oper | 45 | 2 | 3 |
| Zero Page,X | EOR Oper,X | 55 | 2 | 4 |
| Absolute | EOR Oper | 40 | 3 | 4 |
| Absolute,X | EOR Oper,X | 50 | 3 | 4* |
| Absolute,Y | EOR Oper,Y | 59 | 3 | 4* |
| (Indirect,X) | EOR (Oper,X) | 41 | 2 | 6 |
| (Indirect),Y | EOR (Oper),Y | 51 | 2 | 5* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if page boundary is crossed.
INC INC Increment memory by one INC
N Z C I D V
Operation: M + 1 -> M / / _ _ _ _
(Ref: 10.6)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Zero Page | INC Oper | E6 | 2 | 5 |
| Zero Page,X | INC Oper,X | F6 | 2 | 6 |
| Absolute | INC Oper | EE | 3 | 6 |
| Absolute,X | INC Oper,X | FE | 3 | 7 |
+----------------+-----------------------+---------+---------+----------+
INX INX Increment Index X by one INX
N Z C I D V
Operation: X + 1 -> X / / _ _ _ _
(Ref: 7.4)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | INX | E8 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
BASIC TO MACHINE LANGUAGE 243
~
INY INY Increment Index Y by one INY
Operation: X + 1 -> X N Z C I D V
/ / _ _ _ _
(Ref: 7.5)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | INY | C8 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
JMP JMP Jump to new location JMP
Operation: (PC + 1) -> PCL N Z C I D V
(PC + 2) -> PCH (Ref: 4.0.2) _ _ _ _ _ _
(Ref: 9.8.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Absolute | JMP Oper | 4C | 3 | 3 |
| Indirect | JMP (Oper) | 6C | 3 | 5 |
+----------------+-----------------------+---------+---------+----------+
JSR JSR Jump to new location saving return address JSR
Operation: PC + 2 toS, (PC + 1) -> PCL N Z C I D V
(PC + 2) -> PCH _ _ _ _ _ _
(Ref: 8.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Absolute | JSR Oper | 20 | 3 | 6 |
+----------------+-----------------------+---------+---------+----------+
244 BASIC TO MACHINE LANGUAGE
~
LDA LDA Load accumulator with memory LDA
Operation: M -> A N Z C I D V
/ / _ _ _ _
(Ref: 2.1.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | LDA #Oper | A9 | 2 | 2 |
| Zero Page | LDA Oper | A5 | 2 | 3 |
| Zero Page,X | LDA Oper,X | B5 | 2 | 4 |
| Absolute | LDA Oper | AD | 3 | 4 |
| Absolute,X | LDA Oper,X | BD | 3 | 4* |
| Absolute,Y | LDA Oper,Y | B9 | 3 | 4* |
| (Indirect,X) | LDA (Oper,X) | A1 | 2 | 6 |
| (Indirect),Y | LDA (Oper),Y | B1 | 2 | 5* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if page boundary is crossed.
LDX LDX Load index X with memory LDX
Operation: M -> X N Z C I D V
/ / _ _ _ _
(Ref: 7.0)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | LDX #Oper | A2 | 2 | 2 |
| Zero Page | LDX Oper | A6 | 2 | 3 |
| Zero Page,Y | LDX Oper,Y | B6 | 2 | 4 |
| Absolute | LDX Oper | AE | 3 | 4 |
| Absolute,Y | LDX Oper,Y | BE | 3 | 4* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 when page boundary is crossed.
BASIC TO MACHINE LANGUAGE 245
~
LDY LDY Load index Y with memory LDY
N Z C I D V
Operation: M -> Y / / _ _ _ _
(Ref: 7.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | LDY #Oper | A0 | 2 | 2 |
| Zero Page | LDY Oper | A4 | 2 | 3 |
| Zero Page,X | LDY Oper,X | B4 | 2 | 4 |
| Absolute | LDY Oper | AC | 3 | 4 |
| Absolute,X | LDY Oper,X | BC | 3 | 4* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 when page boundary is crossed.
LSR LSR Shift right one bit (memory or accumulator) LSR
+-+-+-+-+-+-+-+-+
Operation: 0 -> |7|6|5|4|3|2|1|0| -> C N Z C I D V
+-+-+-+-+-+-+-+-+ 0 / / _ _ _
(Ref: 10.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Accumulator | LSR A | 4A | 1 | 2 |
| Zero Page | LSR Oper | 46 | 2 | 5 |
| Zero Page,X | LSR Oper,X | 56 | 2 | 6 |
| Absolute | LSR Oper | 4E | 3 | 6 |
| Absolute,X | LSR Oper,X | 5E | 3 | 7 |
+----------------+-----------------------+---------+---------+----------+
NOP NOP No operation NOP
N Z C I D V
Operation: No Operation (2 cycles) _ _ _ _ _ _
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | NOP | EA | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
246 BASIC TO MACHINE LANGUAGE
~
ORA ORA "OR" memory with accumulator ORA
Operation: A V M -> A N Z C I D V
/ / _ _ _ _
(Ref: 2.2.3.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | ORA #Oper | 09 | 2 | 2 |
| Zero Page | ORA Oper | 05 | 2 | 3 |
| Zero Page,X | ORA Oper,X | 15 | 2 | 4 |
| Absolute | ORA Oper | 0D | 3 | 4 |
| Absolute,X | ORA Oper,X | 10 | 3 | 4* |
| Absolute,Y | ORA Oper,Y | 19 | 3 | 4* |
| (Indirect,X) | ORA (Oper,X) | 01 | 2 | 6 |
| (Indirect),Y | ORA (Oper),Y | 11 | 2 | 5 |
+----------------+-----------------------+---------+---------+----------+
* Add 1 on page crossing
PHA PHA Push accumulator on stack PHA
Operation: A toS N Z C I D V
_ _ _ _ _ _
(Ref: 8.5)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | PHA | 48 | 1 | 3 |
+----------------+-----------------------+---------+---------+----------+
PHP PHP Push processor status on stack PHP
Operation: P toS N Z C I D V
_ _ _ _ _ _
(Ref: 8.11)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | PHP | 08 | 1 | 3 |
+----------------+-----------------------+---------+---------+----------+
BASIC TO MACHINE LANGUAGE 247
~
PLA PLA Pull accumulator from stack PLA
Operation: A fromS N Z C I D V
_ _ _ _ _ _
(Ref: 8.6)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | PLA | 68 | 1 | 4 |
+----------------+-----------------------+---------+---------+----------+
PLP PLP Pull processor status from stack PLA
Operation: P fromS N Z C I D V
From Stack
(Ref: 8.12)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | PLP | 28 | 1 | 4 |
+----------------+-----------------------+---------+---------+----------+
ROL ROL Rotate one bit left (memory or accumulator) ROL
+------------------------------+
| M or A |
| +-+-+-+-+-+-+-+-+ +-+ |
Operation: +-< |7|6|5|4|3|2|1|0| <- |C| <-+ N Z C I D V
+-+-+-+-+-+-+-+-+ +-+ / / / _ _ _
(Ref: 10.3)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Accumulator | ROL A | 2A | 1 | 2 |
| Zero Page | ROL Oper | 26 | 2 | 5 |
| Zero Page,X | ROL Oper,X | 36 | 2 | 6 |
| Absolute | ROL Oper | 2E | 3 | 6 |
| Absolute,X | ROL Oper,X | 3E | 3 | 7 |
+----------------+-----------------------+---------+---------+----------+
248 BASIC TO MACHINE LANGUAGE
~
ROR ROR Rotate one bit right (memory or accumulator) ROR
+------------------------------+
| |
| +-+ +-+-+-+-+-+-+-+-+ |
Operation: +-> |C| -> |7|6|5|4|3|2|1|0| >-+ N Z C I D V
+-+ +-+-+-+-+-+-+-+-+ / / / _ _ _
(Ref: 10.4)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Accumulator | ROR A | 6A | 1 | 2 |
| Zero Page | ROR Oper | 66 | 2 | 5 |
| Zero Page,X | ROR Oper,X | 76 | 2 | 6 |
| Absolute | ROR Oper | 6E | 3 | 6 |
| Absolute,X | ROR Oper,X | 7E | 3 | 7 |
+----------------+-----------------------+---------+---------+----------+
Note: ROR instruction is available on MCS650X microprocessors after
June, 1976.
RTI RTI Return from interrupt RTI
N Z C I D V
Operation: P fromS PC fromS From Stack
(Ref: 9.6)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | RTI | 4D | 1 | 6 |
+----------------+-----------------------+---------+---------+----------+
RTS RTS Return from subroutine RTS
N Z C I D V
Operation: PC fromS, PC + 1 -> PC _ _ _ _ _ _
(Ref: 8.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | RTS | 60 | 1 | 6 |
+----------------+-----------------------+---------+---------+----------+
BASIC TO MACHINE LANGUAGE 249
~
SBC SBC Subtract memory from accumulator with borrow SBC
-
Operation: A - M - C -> A N Z C I D V
- / / / _ _ /
Note:C = Borrow (Ref: 2.2.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | SBC #Oper | E9 | 2 | 2 |
| Zero Page | SBC Oper | E5 | 2 | 3 |
| Zero Page,X | SBC Oper,X | F5 | 2 | 4 |
| Absolute | SBC Oper | ED | 3 | 4 |
| Absolute,X | SBC Oper,X | FD | 3 | 4* |
| Absolute,Y | SBC Oper,Y | F9 | 3 | 4* |
| (Indirect,X) | SBC (Oper,X) | E1 | 2 | 6 |
| (Indirect),Y | SBC (Oper),Y | F1 | 2 | 5 |
+----------------+-----------------------+---------+---------+----------+
* Add 1 when page boundary is crossed.
SEC SEC Set carry flag SEC
Operation: 1 -> C N Z C I D V
_ _ 1 _ _ _
(Ref: 3.0.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | SEC | 38 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
SED SED Set decimal mode SED
N Z C I D V
Operation: 1 -> D _ _ _ _ 1 _
(Ref: 3.3.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | SED | F8 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
250 BASIC TO MACHINE LANGUAGE
~
SEI SEI Set interrupt disable status SED
N Z C I D V
Operation: 1 -> I _ _ _ 1 _ _
(Ref: 3.2.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | SEI | 78 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
STA STA Store accumulator in memory STA
Operation: A -> M N Z C I D V
_ _ _ _ _ _
(Ref: 2.1.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Zero Page | STA Oper | 85 | 2 | 3 |
| Zero Page,X | STA Oper,X | 95 | 2 | 4 |
| Absolute | STA Oper | 80 | 3 | 4 |
| Absolute,X | STA Oper,X | 90 | 3 | 5 |
| Absolute,Y | STA Oper, Y | 99 | 3 | 5 |
| (Indirect,X) | STA (Oper,X) | 81 | 2 | 6 |
| (Indirect),Y | STA (Oper),Y | 91 | 2 | 6 |
+----------------+-----------------------+---------+---------+----------+
STX STX Store index X in memory STX
Operation: X -> M N Z C I D V
_ _ _ _ _ _
(Ref: 7.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Zero Page | STX Oper | 86 | 2 | 3 |
| Zero Page,Y | STX Oper,Y | 96 | 2 | 4 |
| Absolute | STX Oper | 8E | 3 | 4 |
+----------------+-----------------------+---------+---------+----------+
BASIC TO MACHINE LANGUAGE 251
~
STY STY Store index Y in memory STY
Operation: Y -> M N Z C I D V
_ _ _ _ _ _
(Ref: 7.3)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Zero Page | STY Oper | 84 | 2 | 3 |
| Zero Page,X | STY Oper,X | 94 | 2 | 4 |
| Absolute | STY Oper | 8C | 3 | 4 |
+----------------+-----------------------+---------+---------+----------+
TAX TAX Transfer accumulator to index X TAX
Operation: A -> X N Z C I D V
/ / _ _ _ _
(Ref: 7.11)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | TAX | AA | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
TAY TAY Transfer accumulator to index Y TAY
Operation: A -> Y N Z C I D V
/ / _ _ _ _
(Ref: 7.13)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | TAY | A8 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
252 BASIC TO MACHINE LANGUAGE
~
TSX TSX Transfer stack pointer to index X TSX
Operation: S -> X N Z C I D V
/ / _ _ _ _
(Ref: 8.9)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | TSX | BA | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
TXA TXA Transfer index X to accumulator TXA
N Z C I D V
Operation: X -> A / / _ _ _ _
(Ref: 7.12)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | TXA | 8A | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
TXS TXS Transfer index X to stack pointer TXS
N Z C I D V
Operation: X -> S _ _ _ _ _ _
(Ref: 8.8)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | TXS | 9A | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
TYA TYA Transfer index Y to accumulator TYA
Operation: Y -> A N Z C I D V
/ / _ _ _ _
(Ref: 7.14)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | TYA | 98 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
BASIC TO MACHINE LANGUAGE 253
~
+------------------------------------------------------------------------
| INSTRUCTION ADDRESSING MODES AND RELATED EXECUTION TIMES
| (in clock cycles)
+------------------------------------------------------------------------
A A A B B B B B B B B B B C
D N S C C E I M N P R V V L
C D L C S Q T I E L K C S C
Accumulator | . . 2 . . . . . . . . . . .
Immediate | 2 2 . . . . . . . . . . .
Zero Page | 3 3 5 . . . 3 . . . . . . .
Zero Page,X | 4 4 6 . . . . . . . . . . .
Zero Page,Y | . . . . . . . . . . . . . .
Absolute | 4 4 6 . . . 4 . . . . . . .
Absolute,X | 4* 4* 7 . . . . . . . . . . .
Absolute,Y | 4* 4* . . . . . . . . . . . .
Implied | . . . . . . . . . . . . . 2
Relative | . . . 2** 2** 2** . 2** 2** 2** 7 2** 2** .
(Indirect,X) | 6 6 . . . . . . . . . . . .
(Indirect),Y | 5* 5* . . . . . . . . . . . .
Abs. Indirect| . . . . . . . . . . . . . .
+-----------------------------------------------------------
C C C C C C D D D E I I I J
L L L M P P E E E O N N N M
D I V P X Y C X Y R C X Y P
Accumulator | . . . . . . . . . . . . . .
Immediate | . . . 2 2 2 . . . 2 . . . .
Zero Page | . . . 3 3 3 5 . . 3 5 . . .
Zero Page,X | . . . 4 . . 6 . . 4 6 . . .
Zero Page,Y | . . . . . . . . . . . . . .
Absolute | . . . 4 4 4 6 . . 4 6 . . 3
Absolute,X | . . . 4* . . 7 . . 4* 7 . . .
Absolute,Y | . . . 4* . . . . . 4* . . . .
Implied | 2 2 2 . . . . 2 2 . . 2 2 .
Relative | . . . . . . . . . . . . . .
(Indirect,X) | . . . 6 . . . . . 6 . . . .
(Indirect),Y | . . . 5* . . . . . 5* . . . .
Abs. Indirect| . . . . . . . . . . . . . 5
+-----------------------------------------------------------
* Add one cycle if indexing across page boundary
** Add one cycle if branch is taken, Add one additional if branching
operation crosses page boundary
254 BASIC TO MACHINE LANGUAGE
~
------------------------------------------------------------------------+
INSTRUCTION ADDRESSING MODES AND RELATED EXECUTION TIMES |
(in clock cycles) |
------------------------------------------------------------------------+
J L L L L N O P P P P R R R
S D D D S O R H H L L O O T
R A X Y R P A A P A P L R I
Accumulator | . . . . 2 . . . . . . 2 2 .
Immediate | . 2 2 2 . . 2 . . . . . . .
Zero Page | . 3 3 3 5 . 3 . . . . 5 5 .
Zero Page,X | . 4 . 4 6 . 4 . . . . 6 6 .
Zero Page,Y | . . 4 . . . . . . . . . . .
Absolute | 6 4 4 4 6 . 4 . . . . 6 6 .
Absolute,X | . 4* . 4* 7 . 4* . . . . 7 7 .
Absolute,Y | . 4* 4* . . . 4* . . . . . . .
Implied | . . . . . 2 . 3 3 4 4 . . 6
Relative | . . . . . . . . . . . . . .
(Indirect,X) | . 6 . . . . 6 . . . . . . .
(Indirect),Y | . 5* . . . . 5* . . . . . . .
Abs. Indirect| . . . . . . . . . . . . . .
+-----------------------------------------------------------
R S S S S S S S T T T T T T
T B E E E T T T A A S X X Y
S C C D I A X Y X Y X A S A
Accumulator | . . . . . . . . . . . . . .
Immediate | . 2 . . . . . . . . . . . .
Zero Page | . 3 . . . 3 3 3 . . . . . .
Zero Page,X | . 4 . . . 4 . 4 . . . . . .
Zero Page,Y | . . . . . . 4 . . . . . . .
Absolute | . 4 . . . 4 4 4 . . . . . .
Absolute,X | . 4* . . . 5 . . . . . . . .
Absolute,Y | . 4* . . . 5 . . . . . . . .
Implied | 6 . 2 2 2 . . . 2 2 2 2 2 2
Relative | . . . . . . . . . . . . . .
(Indirect,X) | . 6 . . . 6 . . . . . . . .
(Indirect),Y | . 5* . . . 6 . . . . . . . .
Abs. Indirect| . . . . . . . . . . . . . .
+-----------------------------------------------------------
* Add one cycle if indexing across page boundary
** Add one cycle if branch is taken, Add one additional if branching
operation crosses page boundary
BASIC TO MACHINE LANGUAGE 255
~
00 - BRK 20 - JSR
01 - ORA - (Indirect,X) 21 - AND - (Indirect,X)
02 - Future Expansion 22 - Future Expansion
03 - Future Expansion 23 - Future Expansion
04 - Future Expansion 24 - BIT - Zero Page
05 - ORA - Zero Page 25 - AND - Zero Page
06 - ASL - Zero Page 26 - ROL - Zero Page
07 - Future Expansion 27 - Future Expansion
08 - PHP 28 - PLP
09 - ORA - Immediate 29 - AND - Immediate
0A - ASL - Accumulator 2A - ROL - Accumulator
0B - Future Expansion 2B - Future Expansion
0C - Future Expansion 2C - BIT - Absolute
0D - ORA - Absolute 2D - AND - Absolute
0E - ASL - Absolute 2E - ROL - Absolute
0F - Future Expansion 2F - Future Expansion
10 - BPL 30 - BMI
11 - ORA - (Indirect),Y 31 - AND - (Indirect),Y
12 - Future Expansion 32 - Future Expansion
13 - Future Expansion 33 - Future Expansion
14 - Future Expansion 34 - Future Expansion
15 - ORA - Zero Page,X 35 - AND - Zero Page,X
16 - ASL - Zero Page,X 36 - ROL - Zero Page,X
17 - Future Expansion 37 - Future Expansion
18 - CLC 38 - SEC
19 - ORA - Absolute,Y 39 - AND - Absolute,Y
1A - Future Expansion 3A - Future Expansion
1B - Future Expansion 3B - Future Expansion
1C - Future Expansion 3C - Future Expansion
1D - ORA - Absolute,X 3D - AND - Absolute,X
1E - ASL - Absolute,X 3E - ROL - Absolute,X
1F - Future Expansion 3F - Future Expansion
256 BASIC TO MACHINE LANGUAGE
~
40 - RTI 60 - RTS
41 - EOR - (Indirect,X) 61 - ADC - (Indirect,X)
42 - Future Expansion 62 - Future Expansion
43 - Future Expansion 63 - Future Expansion
44 - Future Expansion 64 - Future Expansion
45 - EOR - Zero Page 65 - ADC - Zero Page
46 - LSR - Zero Page 66 - ROR - Zero Page
47 - Future Expansion 67 - Future Expansion
48 - PHA 68 - PLA
49 - EOR - Immediate 69 - ADC - Immediate
4A - LSR - Accumulator 6A - ROR - Accumulator
4B - Future Expansion 6B - Future Expansion
4C - JMP - Absolute 6C - JMP - Indirect
4D - EOR - Absolute 6D - ADC - Absolute
4E - LSR - Absolute 6E - ROR - Absolute
4F - Future Expansion 6F - Future Expansion
50 - BVC 70 - BVS
51 - EOR - (Indirect),Y 71 - ADC - (Indirect),Y
52 - Future Expansion 72 - Future Expansion
53 - Future Expansion 73 - Future Expansion
54 - Future Expansion 74 - Future Expansion
55 - EOR - Zero Page,X 75 - ADC - Zero Page,X
56 - LSR - Zero Page,X 76 - ROR - Zero Page,X
57 - Future Expansion 77 - Future Expansion
58 - CLI 78 - SEI
59 - EOR - Absolute,Y 79 - ADC - Absolute,Y
5A - Future Expansion 7A - Future Expansion
5B - Future Expansion 7B - Future Expansion
5C - Future Expansion 7C - Future Expansion
50 - EOR - Absolute,X 70 - ADC - Absolute,X
5E - LSR - Absolute,X 7E - ROR - Absolute,X
5F - Future Expansion 7F - Future Expansion
BASIC TO MACHINE LANGUAGE 257
~
80 - Future Expansion A0 - LDY - Immediate
81 - STA - (Indirect,X) A1 - LDA - (Indirect,X)
82 - Future Expansion A2 - LDX - Immediate
83 - Future Expansion A3 - Future Expansion
84 - STY - Zero Page A4 - LDY - Zero Page
85 - STA - Zero Page A5 - LDA - Zero Page
86 - STX - Zero Page A6 - LDX - Zero Page
87 - Future Expansion A7 - Future Expansion
88 - DEY A8 - TAY
89 - Future Expansion A9 - LDA - Immediate
8A - TXA AA - TAX
8B - Future Expansion AB - Future Expansion
8C - STY - Absolute AC - LDY - Absolute
80 - STA - Absolute AD - LDA - Absolute
8E - STX - Absolute AE - LDX - Absolute
8F - Future Expansion AF - Future Expansion
90 - BCC B0 - BCS
91 - STA - (Indirect),Y B1 - LDA - (Indirect),Y
92 - Future Expansion B2 - Future Expansion
93 - Future Expansion B3 - Future Expansion
94 - STY - Zero Page,X B4 - LDY - Zero Page,X
95 - STA - Zero Page,X BS - LDA - Zero Page,X
96 - STX - Zero Page,Y B6 - LDX - Zero Page,Y
97 - Future Expansion B7 - Future Expansion
98 - TYA B8 - CLV
99 - STA - Absolute,Y B9 - LDA - Absolute,Y
9A - TXS BA - TSX
9B - Future Expansion BB - Future Expansion
9C - Future Expansion BC - LDY - Absolute,X
90 - STA - Absolute,X BD - LDA - Absolute,X
9E - Future Expansion BE - LDX - Absolute,Y
9F - Future Expansion BF - Future Expansion
258 BASIC TO MACHINE LANGUAGE
~
C0 - Cpy - Immediate E0 - CPX - Immediate
C1 - CMP - (Indirect,X) E1 - SBC - (Indirect,X)
C2 - Future Expansion E2 - Future Expansion
C3 - Future Expansion E3 - Future Expansion
C4 - CPY - Zero Page E4 - CPX - Zero Page
C5 - CMP - Zero Page E5 - SBC - Zero Page
C6 - DEC - Zero Page E6 - INC - Zero Page
C7 - Future Expansion E7 - Future Expansion
C8 - INY E8 - INX
C9 - CMP - Immediate E9 - SBC - Immediate
CA - DEX EA - NOP
CB - Future Expansion EB - Future Expansion
CC - CPY - Absolute EC - CPX - Absolute
CD - CMP - Absolute ED - SBC - Absolute
CE - DEC - Absolute EE - INC - Absolute
CF - Future Expansion EF - Future Expansion
D0 - BNE F0 - BEQ
D1 - CMP (Indirect@,Y F1 - SBC - (Indirect),Y
D2 - Future Expansion F2 - Future Expansion
D3 - Future Expansion F3 - Future Expansion
D4 - Future Expansion F4 - Future Expansion
D5 - CMP - Zero Page,X F5 - SBC - Zero Page,X
D6 - DEC - Zero Page,X F6 - INC - Zero Page,X
D7 - Future Expansion F7 - Future Expansion
D8 - CLD F8 - SED
D9 - CMP - Absolute,Y F9 - SBC - Absolute,Y
DA - Future Expansion FA - Future Expansion
DB - Future Expansion FB - Future Expansion
DC - Future Expansion FC - Future Expansion
DD - CMP - Absolute,X FD - SBC - Absolute,X
DE - DEC - Absolute,X FE - INC - Absolute,X
DF - Future Expansion FF - Future Expansion
BASIC TO MACHINE LANGUAGE 259
~
MEMORY MANAGEMENT ON THE
COMMODORE 64
The Commodore 64 has 64K bytes of RAM. It also has 20K bytes of ROM,
containing BASIC, the operating system, and the standard character set.
It also accesses input/output devices as a 4K chunk of memory. How is
this all possible on a computer with a 16-bit address bus, that is
normally only capable of addressing 64K?
The secret is in the 6510 processor chip itself. On the chip is an
input/output port. This port is used to control whether RAM or ROM or I/O
will appear in certain portions of the system's memory. The port is also
used to control the Datassette(TM), so it is important to affect only the
proper bits.
The 6510 input/output port appears at location 1. The data direction
register for this port appears at location 0. The port is controlled like
any of the other input/output ports in the system... the data direction
controls whether a given bit will be an input or an output, and the
actual data transfer occurs through the port itself. The lines in the
6510 control port are defined as follows:
+---------+---+------------+--------------------------------------------+
| NAME |BIT| DIRECTION | DESCRIPTION |
+---------+---+------------+--------------------------------------------+
| LORAM | 0 | OUTPUT | Control for RAM/ROM at $A000-$BFFF |
| HIRAM | 1 | OUTPUT | Control for RAM/ROM at $E000-$FFFF |
| CHAREN | 2 | OUTPUT | Control for I/O/ROM at $D000-$DFFF |
| | 3 | OUTPUT | Cassette write line |
| | 4 | INPUT | Cassette switch sense (0=play button down) |
| | 5 | OUTPUT | Cassette motor control (0=motor spins) |
+---------+---+------------+--------------------------------------------+
The proper value for the data direction register is as follows:
BITS 5 4 3 2 1 0
----------------
1 0 1 1 1 1
(where 1 is an output, and 0 is an input).
260 BASIC TO MACHINE LANGUAGE
~
This gives a value of 47 decimal. The Commodore 64 automatically sets
the data direction register to this value.
The control lines, in general, perform the function given in their de-
scriptions. However, a combination of control lines are occasionally used
to get a particular memory configuration.
LORAM (bit 0) can generally be thought of as a control line which banks
the 8K byte BASIC ROM in and out of the microprocessor address space.
Normally, this line is HIGH for BASIC operation. If this line is
programmed LOW, the BASIC ROM will disappear from the memory map and be
replaced by 8K bytes of RAM from $A000-$BFFF.
HIRAM (bit 1) can generally be thought of as a control line which banks
the 8K byte KERNAL ROM in and out of the microprocessor address space.
Normally, this line is HIGH for BASIC operation. If this line is
programmed LOW, the KERNAL ROM will disappear from the memory map and be
replaced by 8K bytes of RAM from $E000-$FFFF.
CHAREN (bit 2) is used only to bank the 4K byte character generator ROM
in or out of the microprocessor address space. From the processor point
of view, the character ROM occupies the same address space as the I/O
devices ($D000-$DFFF). When the CHAREN line is set to 1 (as is normal),
the I/O devices appear in the microprocessor address space, and the
character ROM is not accessable. When the CHAREN bit is cleared to 0, the
character ROM appears in the processor address space, and the I/O devices
are not accessable. (The microprocessor only needs to access the
character ROM when downloading the character set from ROM to RAM. Special
care is needed for this... see the section on PROGRAMMABLE CHARACTERS in
the GRAPHICS chapter). CHAREN can be overridden by other control lines in
certain memory configurations. CHAREN will have no effect on any memory
configuration without I/O devices. RAM will appear from $D000-$DFFF
instead.
+-----------------------------------------------------------------------+
| NOTE: In any memory map containing ROM, a WRITE (a POKE) to a ROM |
| location will store data in the RAM "under" the ROM. Writing to a ROM |
| location stores data in the "hidden" RAM. For example, this allows a |
| hi-resolution screen to be kept underneath a ROM, and be changed |
| without having to bank the screen back into the processor address |
| space. Of course a READ of a ROM location will return the contents of |
| the ROM, not the "hidden" RAM. |
+-----------------------------------------------------------------------+
BASIC TO MACHINE LANGUAGE 261
~
COMMODORE 64 FUNDAMENTAL MEMORY MAP
+----------------------------+
| 8K KERNAL ROM |
E000-FFFF | OR RAM |
+----------------------------+
D000-DFFF | 4K I/O OR RAM OR CHAR. ROM |
+----------------------------+
C000-CFFF | 4K RAM |
+----------------------------+
| 8K BASIC ROM OR RAM |
A000-BFFF | OR ROM PLUG-IN |
+----------------------------+
| 8K RAM |
8000-9FFF | OR ROM PLUG-IN |
+----------------------------+
| |
| |
| 16 K RAM |
4000-7FFF | |
+----------------------------+
| |
| |
| 16 K RAM |
0000-3FFF | |
+----------------------------+
I/O BREAKDOWN
D000-D3FF VIC (Video Controller) 1 K Bytes
D400-D7FF SID (Sound Synthesizer) 1 K Bytes
D800-DBFF Color RAM 1 K Nybbles
DC00-DCFF CIA1 (Keyboard) 256 Bytes
DD00-DDFF CIA2 (Serial Bus, User Port/RS-232) 256 Bytes
DE00-DEFF Open I/O slot #l (CP/M Enable) 256 Bytes
DF00-DFFF Open I/O slot #2 (Disk) 256 Bytes
262 BASIC TO MACHINE LANGUAGE
~
The two open I/O slots are for general purpose user I/O, special pur-
pose I/O cartridges (such as IEEE), and have been tentatively designated
for enabling the Z-80 cartridge (CP/M option) and for interfacing to a
low-cost high-speed disk system.
The system provides for "auto-start" of the program in a Commodore 64
Expansion Cartridge. The cartridge program is started if the first nine
bytes of the cartridge ROM starting at location 32768 ($8000) contain
specific data. The first two bytes must hold the Cold Start vector to be
used by the cartridge program. The next two bytes at 32770 ($8002) must
be the Warm Start vector used by the cartridge program. The next three
bytes must be the letters, CBM, with bit 7 set in each letter. The last
two bytes must be the digits "80" in PET ASCII.
COMMODORE 64 MEMORY MAPS
The following table lists the various memory configurations available
on the COMMODORE 64, the states of the control lines which select each
memory map, and the intended use of each map.
The leftmost column of the table contains addresses in hexadecimal
notation. The columns aside it introduce all possible memory
configurations. The default mode is on the left, and the absolutely most
rarely used Ultimax game console configuration is on the right. Each
memory configuration column has one or more four-digit binary numbers as
a title. The bits, from left to right, represent the state of the /LORAM,
/HIRAM, /GAME and /EXROM lines, respectively. The bits whose state does
not matter are marked with "X". For instance, when the Ultimax video game
configuration is active (the /GAME line is shorted to ground, /EXROM kept
high), the /LORAM and /HIRAM lines have no effect.
BASIC TO MACHINE LANGUAGE 263
~
LHGE LHGE LHGE LHGE LHGE LHGE LHGE LHGE LHGE
1111 101X 1000 011X 001X 1110 0100 1100 XX01
10000 default 00X0 Ultimax
-------------------------------------------------------------------------
F000
Kernal RAM RAM Kernal RAM Kernal Kernal Kernal ROMH(*
E000
-------------------------------------------------------------------------
D000 IO/C IO/C IO/RAM IO/C RAM IO/C IO/C IO/C I/O
-------------------------------------------------------------------------
C000 RAM RAM RAM RAM RAM RAM RAM RAM -
-------------------------------------------------------------------------
B000
BASIC RAM RAM RAM RAM BASIC ROMH ROMH -
A000
-------------------------------------------------------------------------
9000
RAM RAM RAM RAM RAM ROML RAM ROML ROML(*
8000
-------------------------------------------------------------------------
7000
6000
RAM RAM RAM RAM RAM RAM RAM RAM -
5000
4000
-------------------------------------------------------------------------
3000
2000 RAM RAM RAM RAM RAM RAM RAM RAM -
1000
-------------------------------------------------------------------------
0000 RAM RAM RAM RAM RAM RAM RAM RAM RAM
-------------------------------------------------------------------------
NOTE: (1) (2) (3) (4) (5) (6) (7) (8) (9)
*) Internal memory does not respond to write accesses to these areas.
264 BASIC TO MACHINE LANGUAGE
~
Legend: Kernal E000-FFFF Kernal ROM.
IO/C D000-DFFF I/O address space or Character
generator ROM, selected by -CHAREN.
If the CHAREN bit is clear,
the character generator ROM is
chosen. If it is set, the
I/O chips are accessible.
IO/RAM D000-DFFF I/O address space or RAM,
selected by -CHAREN.
If the CHAREN bit is clear,
the character generator ROM is
chosen. If it is set, the
internal RAM is accessible.
I/O D000-DFFF I/O address space.
The -CHAREN line has no effect.
BASIC A000-BFFF BASIC ROM.
ROMH A000-BFFF or External ROM with the -ROMH line
E000-FFFF connected to its -CS line.
ROML 8000-9FFF External ROM with the -ROML line
connected to its -CS line.
RAM various ranges Commodore 64's internal RAM.
- 1000-7FFF and Open address space.
A000-CFFF The Commodore 64's memory chips
do not detect any memory accesses
to this area except the VIC-II's
DMA and memory refreshes.
BASIC TO MACHINE LANGUAGE 265
~
(1) This is the default BASIC memory map which provides
BASIC 2.0 and 38K contiguous bytes of user RAM.
(2) This map provides 60K bytes of RAM and I/O devices.
The user must write his own I/O driver routines.
(3) The same as 2, but the character ROM is not
accessible by the CPU in this map.
(4) This map is intended for use with softload languages
(including CP/M), providing 52K contiguous bytes of
user RAM, I/O devices, and I/O driver routines.
(5) This map gives access to all 64K bytes of RAM. The
I/O devices must be banked back into the processor's
address space for any I/O operation.
(6) This is the standard configuration for a BASIC system
with a BASIC expansion ROM. This map provides 32K
contiguous bytes of user RAM and up to 8K bytes of
BASIC "enhancement".
(7) This map provides 40K contiguous bytes of user RAM
and up to 8K bytes of plug-in ROM for special ROM-
based applications which don't require BASIC.
(8) This map provides 32K contiguous bytes of user RAM
and up to 16K bytes of plug-in ROM for special
applications which don't require BASIC (word
processors, other languages, etc.).
(9) This is the ULTIMAX video game memory map. Note that
the 2K byte "expansion RAM" for the ULTIMAX, if
required, is accessed out of the COMMODORE 64 and
any RAM in the cartridge is ignored.
266 BASIC TO MACHINE LANGUAGE
~
BASIC TO MACHINE LANGUAGE 267
~
THE KERNAL
One of the problems facing programmers in the microcomputer field is
the question of what to do when changes are made to the operating system
of the computer by the company. Machine language programs which took much
time to develop might no longer work, forcing major revisions in the
program. To alleviate this problem, Commodore has developed a method of
protecting software writers called the KERNAL.
Essentially, the KERNAL is a standardized JUMP TABLE to the input,
output, and memory management routines in the operating system. The
locations of each routine in ROM may change as the system is upgraded.
But the KERNAL jump table will always be changed to match. If your
machine language routines only use the system ROM routines through the
KERNAL, it will take much less work to modify them, should that need ever
arise.
The KERNAL is the operating system of the Commodore 64 computer. All
input, output, and memory management is controlled by the KERNAL.
To simplify the machine language programs you write, and to make sure
that future versions of the Commodore 64 operating system don't make your
machine language programs obsolete, the KERNAL contains a jump table for
you to use. By taking advantage of the 39 input/output routines and other
utilities available to you from the table, not only do you save time, you
also make it easier to translate your programs from one Commodore
computer to another.
The jump table is located on the last page of memory, in read-only
memory (ROM).
To use the KERNAL jump table, first you set up the parameters that the
KERNAL routine needs to work. Then JSR (Jump to SubRoutine) to the proper
place in the KERNAL jump table. After performing its function, the KERNAL
transfers control back to your machine language program. Depending on
which KERNAL routine you are using, certain registers may pass parameters
back to your program. The particular registers for each KERNAL routine
may be found in the individual descriptions of the KERNAL subroutines.
268 BASIC TO MACHINE LANGUAGE
~
A good question at this point is why use the jump table at all? Why not
just JSR directly to the KERNAL subroutine involved? The jump table is
used so that if the KERNAL or BASIC is changed, your machine language
programs will still work. In future operating systems the routines may
have their memory locations moved around to a different position in the
memory map... but the jump table will still work correctly!
KERNAL POWER-UP ACTIVITIES
1) On power-up, the KERNAL first resets the stack pointer, and clears
decimal mode.
2) The KERNAL then checks for the presence of an autostart ROM cartridge
at location $8000 HEX (32768 decimal). If this is present, normal
initialization is suspended, and control is transferred to the car-
tridge code. If an autostart ROM is not present, normal system ini-
tialization continues.
3) Next, the KERNAL initializes all INPUT/OUTPUT devices. The serial bus
is initialized. Both 6526 CIA chips are set to the proper values for
keyboard scanning, and the 60-Hz timer is activated. The SID chip is
cleared. The BASIC memory map is selected and the cassette motor is
switched off.
4) Next, the KERNAL performs a RAM test, setting the top and bottom of
memory pointers. Also, page zero is initialized, and the tape buffer
is set up.
The RAM TEST routine is a nondestructive test starting at location
$0300 and working upward. Once the test has found the first non-RAM
location, the top of RAM has its pointer set. The bottom of memory is
always set to $0800, and the screen setup is always set at $0400.
5) Finally, the KERNAL performs these other activities. I/O vectors are
set to default values. The indirect jump table in low memory is estab-
lished. The screen is then cleared, and all screen editor variables
reset. Then the indirect at $A000 is used to start BASIC.
BASIC TO MACHINE LANGUAGE 269
~
HOW TO USE THE KERNAL
When writing machine language programs it is often convenient to use
the routines which are already part of the operating system for input/
output, access to the system clock, memory management, and other similar
operations. It is an unnecessary duplication of effort to write these
routines over and over again, so easy access to the operating system
helps speed machine language programming.
As mentioned before, the KERNAL is a jump table. This is just a col-
lection of JMP instructions to many operating system routines.
To use a KERNAL routine you must first make all of the preparations
that the routine demands. If one routine says that you must call another
KERNAL routine first, then that routine must be called. If the routine
expects you to put a number in the accumulator, then that number must be
there. Otherwise your routines have little chance of working the way you
expect them to work.
After all preparations are made, you must call the routine by means of
the JSR instruction. All KERNAL routines you can access are structured as
SUBROUTINES, and must end with an RTS instruction. When the KERNAL
routine has finished its task, control is returned to your program at the
instruction after the JSR.
Many of the KERNAL routines return error codes in the status word or
the accumulator if you have problems in the routine. Good programming
practice and the success of your machine language programs demand that
you handle this properly. If you ignore an error return, the rest of your
program might "bomb."
That's all there is to do when you're using the KERNAL. Just these
three simple steps:
1) Set up
2) Call the routine
3) Error handling
270 BASIC TO MACHINE LANGUAGE
~
The following conventions are used in describing the KERNAL routines:
- FUNCTION NAME: Name of the KERNAL routine.
- CALL ADDRESS: This is the call address of the KERNAL routine, given in
hexadecimal.
- COMMUNICATION REGISTERS: Registers listed under this heading are used
to pass parameters to and from the KERNAL routines.
- PREPARATORY ROUTINES: Certain KERNAL routines require that data be set
up before they can operate. The routines needed are listed here.
- ERROR RETURNS: A return from a KERNAL routine with the CARRY set
indicates that an error was encountered in processing. The accumulator
will contain the number of the error.
- STACK REQUIREMENTS: This is the actual number of stack bytes used by
the KERNAL routine.
- REGISTERS AFFECTED: All registers used by the KERNAL routine are listed
here.
- DESCRIPTION: A short tutorial on the function of the KERNAL routine is
given here.
The list of the KERNAL routines follows.
BASIC TO MACHINE LANGUAGE 271
~
USER CALLABLE KERNAL ROUTINES
+--------+-------------------+------------------------------------------+
| | ADDRESS | |
| NAME +---------+---------+ FUNCTION |
| | HEX | DECIMAL | |
+--------+---------+---------+------------------------------------------+
| ACPTR | $FFA5 | 65445 | Input byte from serial port |
| CHKIN | $FFC6 | 65478 | Open channel for input |
| CHKOUT | $FFC9 | 65481 | Open channel for output |
| CHRIN | $FFCF | 65487 | Input character from channel |
| CHROUT | $FFD2 | 65490 | Output character to channel |
| CIOUT | $FFA8 | 65448 | Output byte to serial port |
| CINT | $FF81 | 65409 | Initialize screen editor |
| CLALL | $FFE7 | 65511 | Close all channels and files |
| CLOSE | $FFC3 | 65475 | Close a specified logical file |
| CLRCHN | $FFCC | 65484 | Close input and output channels |
| GETIN | $FFE4 | 65508 | Get character from keyboard queue |
| | | | (keyboard buffer) |
| IOBASE | $FFF3 | 65523 | Returns base address of I/O devices |
| IOINIT | $FF84 | 65412 | Initialize input/output |
| LISTEN | $FFB1 | 65457 | Command devices on the serial bus to |
| | | | LISTEN |
| LOAD | $FFD5 | 65493 | Load RAM from a device |
| MEMBOT | $FF9C | 65436 | Read/set the bottom of memory |
| MEMTOP | $FF99 | 65433 | Read/set the top of memory |
| OPEN | $FFC0 | 65472 | Open a logical file |
+--------+---------+---------+------------------------------------------+
272 BASIC TO MACHINE LANGUAGE
~
+--------+-------------------+------------------------------------------+
| | ADDRESS | |
| NAME +---------+---------+ FUNCTION |
| | HEX | DECIMAL | |
+--------+---------+---------+------------------------------------------+
| PLOT | $FFF0 | 65520 | Read/set X,Y cursor position |
| RAMTAS | $FF87 | 65415 | Initialize RAM, allocate tape buffer, |
| | | | set screen $0400 |
| RDTIM | $FFDE | 65502 | Read real time clock |
| READST | $FFB7 | 65463 | Read I/O status word |
| RESTOR | $FF8A | 65418 | Restore default I/O vectors |
| SAVE | $FFD8 | 65496 | Save RAM to device |
| SCNKEY | $FF9F | 65439 | Scan keyboard |
| SCREEN | $FFED | 65517 | Return X,Y organization of screen |
| SECOND | $FF93 | 65427 | Send secondary address after LISTEN |
| SETLFS | $FFBA | 65466 | Set logical, first, and second addresses|
| SETMSG | $FF90 | 65424 | Control KERNAL messages |
| SETNAM | $FFBD | 65469 | Set file name |
| SETTIM | $FFDB | 65499 | Set real time clock |
| SETTMO | $FFA2 | 65442 | Set timeout on serial bus |
| STOP | $FFE1 | 65505 | Scan stop key |
| TALK | $FFB4 | 65460 | Command serial bus device to TALK |
| TKSA | $FF96 | 65430 | Send secondary address after TALK |
| UDTIM | $FFEA | 65514 | Increment real time clock |
| UNLSN | $FFAE | 65454 | Command serial bus to UNLISTEN |
| UNTLK | $FFAB | 65451 | Command serial bus to UNTALK |
| VECTOR | $FF8D | 65421 | Read/set vectored I/O |
+--------+---------+---------+------------------------------------------+
BASIC TO MACHINE LANGUAGE 273
~
B-1. Function Name: ACPTR
Purpose: Get data from the serial bus
Call address: $FFA5 (hex) 65445 (decimal)
Communication registers: A
Preparatory routines: TALK, TKSA
Error returns: See READST
Stack requirements: 13
Registers affected: A, X
Description: This is the routine to use when you want to get informa-
tion from a device on the serial bus, like a disk. This routine gets a
byte of data off the serial bus using full handshaking. The data is
returned in the accumulator. To prepare for this routine the TALK routine
must be called first to command the device on the serial bus to send data
through the bus. If the input device needs a secondary command, it must
be sent by using the TKSA KERNAL routine before calling this routine.
Errors are returned in the status word. The READST routine is used to
read the status word.
How to Use:
0) Command a device on the serial bus to prepare to send data to
the Commodore 64. (Use the TALK and TKSA KERNAL routines.)
1) Call this routine (using JSR).
2) Store or otherwise use the data.
EXAMPLE:
;GET A BYTE FROM THE BUS
JSR ACPTR
STA DATA
274 BASIC TO MACHINE LANGUAGE
~
B-2. Function Name: CHKIN
Purpose: Open a channel for input
Call address: $FFC6 (hex) 65478 (decimal)
Communication registers: X
Preparatory routines: (OPEN)
Error returns:
Stack requirements: None
Registers affected: A, X
Description: Any logical file that has already been opened by the
KERNAL OPEN routine can be defined as an input channel by this routine.
Naturally, the device on the channel must be an input device. Otherwise
an error will occur, and the routine will abort.
If you are getting data from anywhere other than the keyboard, this
routine must be called before using either the CHRIN or the GETIN KERNAL
routines for data input. If you want to use the input from the keyboard,
and no other input channels are opened, then the calls to this routine,
and to the OPEN routine are not needed.
When this routine is used with a device on the serial bus, it auto-
matically sends the talk address (and the secondary address if one was
specified by the OPEN routine) over the bus.
How to Use:
0) OPEN the logical file (if necessary; see description above).
1) Load the X register with number of the logical file to be used.
2) Call this routine (using a JSR command).
Possible errors are:
#3: File not open
#5: Device not present
#6: File not an input file
EXAMPLE:
;PREPARE FOR INPUT FROM LOGICAL FILE 2
LDX #2
JSR CHKIN
BASIC TO MACHINE LANGUAGE 275
~
B-3. Function Name: CHKOUT
Purpose: Open a channel for output
Call address: $FFC9 (hex) 65481 (decimal)
Communication registers: X
Preparatory routines: (OPEN)
Error returns: 0,3,5,7 (See READST)
Stack requirements: 4+
Registers affected: A, X
Description: Any logical file number that has been created by the
KERNAL routine OPEN can be defined as an output channel. Of course, the
device you intend opening a channel to must be an output device.
Otherwise an error will occur, and the routine will be aborted.
This routine must be called before any data is sent to any output
device unless you want to use the Commodore 64 screen as your output
device. If screen output is desired, and there are no other output chan-
nels already defined, then calls to this routine, and to the OPEN routine
are not needed.
When used to open a channel to a device on the serial bus, this routine
will automatically send the LISTEN address specified by the OPEN routine
(and a secondary address if there was one).
How to Use:
+-----------------------------------------------------------------------+
| REMEMBER: this routine is NOT NEEDED to send data to the screen. |
+-----------------------------------------------------------------------+
0) Use the KERNAL OPEN routine to specify a logical file number, a
LISTEN address, and a secondary address (if needed).
1) Load the X register with the logical file number used in the open
statement.
2) Call this routine (by using the JSR instruction).
EXAMPLE:
LDX #3 ;DEFINE LOGICAL FILE 3 AS AN OUTPUT CHANNEL
JSR CHKOUT
Possible errors are:
#3: File not open
#5: Device not present
#7: Not an output file
276 BASIC TO MACHINE LANGUAGE
~
B-4. Function Name: CHRIN
Purpose: Get a character from the input channel
Call address: $FFCF (hex) 65487 (decimal)
Communication registers: A
Preparatory routines: (OPEN, CHKIN)
Error returns: 0 (See READST)
Stack requirements: 7+
Registers affected: A, X
Description: This routine gets a byte of data from a channel already
set up as the input channel by the KERNAL routine CHKIN. If the CHKIN has
NOT been used to define another input channel, then all your data is
expected from the keyboard. The data byte is returned in the accumulator.
The channel remains open after the call.
Input from the keyboard is handled in a special way. First, the cursor
is turned on, and blinks until a carriage return is typed on the
keyboard. All characters on the line (up to 88 characters) are stored in
the BASIC input buffer. These characters can be retrieved one at a time
by calling this routine once for each character. When the carriage return
is retrieved, the entire line has been processed. The next time this
routine is called, the whole process begins again, i.e., by flashing the
cursor.
How to Use:
FROM THE KEYBOARD
1) Retrieve a byte of data by calling this routine.
2) Store the data byte.
3) Check if it is the last data byte (is it a CR?)
4) If not, go to step 1.
EXAMPLE:
LDY $#00 ;PREPARE THE Y REGISTER TO STORE THE DATA
RD JSR CHRIN
STA DATA,Y ;STORE THE YTH DATA BYTE IN THE YTH
;LOCATION IN THE DATA AREA.
INY
CMP #CR ;IS IT A CARRIAGE RETURN?
BNE RD ;NO, GET ANOTHER DATA BYTE
BASIC TO MACHINE LANGUAGE 277
~
EXAMPLE:
JSR CHRIN
STA DATA
FROM OTHER DEVICES
0) Use the KERNAL OPEN and CHKIN routines.
1) Call this routine (using a JSR instruction).
2) Store the data.
EXAMPLE:
JSR CHRIN
STA DATA
B-5. Function Name: CHROUT
Purpose: Output a character
Call address: $FFD2 (hex) 65490 (decimal)
Communication registers: A
Preparatory routines: (CHKOUT,OPEN)
Error returns: 0 (See READST)
Stack requirements: 8+
Registers affected: A
Description: This routine outputs a character to an already opened
channel. Use the KERNAL OPEN and CHKOUT routines to set up the output
channel before calling this routine, If this call is omitted, data is
sent to the default output device (number 3, the screen). The data byte
to be output is loaded into the accumulator, and this routine is called.
The data is then sent to the specified output device. The channel is left
open after the call.
+-----------------------------------------------------------------------+
| NOTE: Care must be taken when using this routine to send data to a |
| specific serial device since data will be sent to all open output |
| channels on the bus. Unless this is desired, all open output channels |
| on the serial bus other than the intended destination channel must be |
| closed by a call to the KERNAL CLRCHN routine. |
+-----------------------------------------------------------------------+
278 BASIC TO MACHINE LANGUAGE
~
How to Use:
0) Use the CHKOUT KERNAL routine if needed, (see description above).
1) Load the data to be output into the accumulator.
2) Call this routine.
EXAMPLE:
;DUPLICATE THE BASIC INSTRUCTION CMD 4,"A";
LDX #4 ;LOGICAL FILE #4
JSR CHKOUT ;OPEN CHANNEL OUT
LDA #'A
JSR CHROUT ;SEND CHARACTER
B-6. Function Name: CIOUT
Purpose: Transmit a byte over the serial bus
Call address: $FFA8 (hex) 65448 (decimal)
Communication registers: A
Preparatory routines: LISTEN, [SECOND]
Error returns: See READST
Stack requirements: 5
Registers affected: None
Description: This routine is used to send information to devices on the
serial bus. A call to this routine will put a data byte onto the serial
bus using full serial handshaking. Before this routine is called, the
LISTEN KERNAL routine must be used to command a device on the serial bus
to get ready to receive data. (If a device needs a secondary address, it
must also be sent by using the SECOND KERNAL routine.) The accumulator is
loaded with a byte to handshake as data on the serial bus. A device must
be listening or the status word will return a timeout. This routine
always buffers one character. (The routine holds the previous character
to be sent back.) So when a call to the KERNAL UNLSN routine is made to
end the data transmission, the buffered character is sent with an End Or
Identify (EOI) set. Then the UNLSN command is sent to the device.
BASIC TO MACHINE LANGUAGE 279
~
How to Use:
0) Use the LISTEN KERNAL routine (and the SECOND routine if needed).
1) Load the accumulator with a byte of data.
2) Call this routine to send the data byte.
EXAMPLE:
LDA #'X ;SEND AN X TO THE SERIAL BUS
JSR CIOUT
B-7. Function Name: CINT
Purpose: Initialize screen editor & 6567 video chip
Call address: $FF81 (hex) 65409 (decimal)
Communication registers: None
Preparatory routines: None
Error returns: None
Stack requirements: 4
Registers affected: A, X, Y
Description: This routine sets up the 6567 video controller chip in the
Commodore 64 for normal operation. The KERNAL screen editor is also
initialized. This routine should be called by a Commodore 64 program
cartridge.
How to Use:
1) Call this routine.
EXAMPLE:
JSR CINT
JMP RUN ;BEGIN EXECUTION
280 BASIC TO MACHINE LANGUAGE
~
B-8. Function Name: CLALL
Purpose: Close all files
Call address: $FFE7 (hex) 65511 (decimal)
Communication registers: None
Preparatory routines: None
Error returns: None
Stack requirements: 11
Registers affected: A, X
Description: This routine closes all open files. When this routine is
called, the pointers into the open file table are reset, closing all
files. Also, the CLRCHN routine is automatically called to reset the I/O
channels.
How to Use:
1) Call this routine.
EXAMPLE:
JSR CLALL ;CLOSE ALL FILES AND SELECT DEFAULT I/O CHANNELS
JMP RUN ;BEGIN EXECUTION
B-9. Function Name: CLOSE
Purpose: Close a logical file
Call address: $FFC3 (hex) 65475 (decimal)
Communication registers: A
Preparatory routines: None
Error returns: 0,240 (See READST)
Stack requirements: 2+
Registers affected: A, X, Y
Description: This routine is used to close a logical file after all I/O
operations have been completed on that file. This routine is called after
the accumulator is loaded with the logical file number to be closed (the
same number used when the file was opened using the OPEN routine).
BASIC TO MACHINE LANGUAGE 281
~
How to Use:
1) Load the accumulator with the number of the logical file to be
closed.
2) Call this routine.
EXAMPLE:
;CLOSE 15
LDA #15
JSR CLOSE
B-10. Function Name: CLRCHN
Purpose: Clear I/O channels
Call address: $FFCC (hex) 65484 (decimal)
Communication registers: None
Preparatory routines: None
Error returns:
Stack requirements: 9
Registers affected: A, X
Description: This routine is called to clear all open channels and re-
store the I/O channels to their original default values. It is usually
called after opening other I/O channels (like a tape or disk drive) and
using them for input/output operations. The default input device is 0
(keyboard). The default output device is 3 (the Commodore 64 screen).
If one of the channels to be closed is to the serial port, an UNTALK
signal is sent first to clear the input channel or an UNLISTEN is sent to
clear the output channel. By not calling this routine (and leaving lis-
tener(s) active on the serial bus) several devices can receive the same
data from the Commodore 64 at the same time. One way to take advantage
of this would be to command the printer to TALK and the disk to LISTEN.
This would allow direct printing of a disk file.
This routine is automatically called when the KERNAL CLALL routine is
executed.
How to Use:
1) Call this routine using the JSR instruction.
EXAMPLE:
JSR CLRCHN
282 BASIC TO MACHINE LANGUAGE
~
B-11. Function Name: GETIN
Purpose: Get a character
Call address: $FFE4 (hex) 65508 (decimal)
Communication registers: A
Preparatory routines: CHKIN, OPEN
Error returns: See READST
Stack requirements: 7+
Registers affected: A (X, Y)
Description: If the channel is the keyboard, this subroutine removes
one character from the keyboard queue and returns it as an ASCII value in
the accumulator. If the queue is empty, the value returned in the
accumulator will be zero. Characters are put into the queue automatically
by an interrupt driven keyboard scan routine which calls the SCNKEY
routine. The keyboard buffer can hold up to ten characters. After the
buffer is filled, additional characters are ignored until at least one
character has been removed from the queue. If the channel is RS-232, then
only the A register is used and a single character is returned. See
READST to check validity. If the channel is serial, cassette, or screen,
call BASIN routine.
How to Use:
1) Call this routine using a JSR instruction.
2) Check for a zero in the accumulator (empty buffer).
3) Process the data.
EXAMPLE:
;WAIT FOR A CHARACTER
WAIT JSR GETIN
CMP #0
BEQ WAIT
BASIC TO MACHINE LANGUAGE 283
~
B-12. Function Name: IOBASE
Purpose: Define I/O memory page
Call address: $FFF3 (hex) 65523 (decimal)
Communication registers: X, Y
Preparatory routines: None
Error returns:
Stack requirements: 2
Registers affected: X, Y
Description: This routine sets the X and Y registers to the address of
the memory section where the memory mapped 110 devices are located. This
address can then be used with an offset to access the memory mapped I/O
devices in the Commodore 64. The offset is the number of locations from
the beginning of the page on which the I/O register you want is located.
The X register contains the low order address byte, while the Y register
contains the high order address byte.
This routine exists to provide compatibility between the Commodore 64,
VIC-20, and future models of the Commodore 64. If the J/0 locations for
a machine language program are set by a call to this routine, they should
still remain compatible with future versions of the Commodore 64, the
KERNAL and BASIC.
How to Use:
1) Call this routine by using the JSR instruction.
2) Store the X and the Y registers in consecutive locations.
3) Load the Y register with the offset.
4) Access that I/O location.
EXAMPLE:
;SET THE DATA DIRECTION REGISTER OF THE USER PORT TO 0 (INPUT)
JSR IOBASE
STX POINT ;SET BASE REGISTERS
STY POINT+1
LDY #2
LDA #0 ;OFFSET FOR DDR OF THE USER PORT
STA (POINT),Y ;SET DDR TO 0
284 BASIC TO MACHINE LANGUAGE
~
B-13. Function Name: IOINIT
Purpose: Initialize I/O devices
Call Address: $FF84 (hex) 65412 (decimal)
Communication registers: None
Preparatory routines: None
Error returns:
Stack requirements: None
Registers affected: A, X, Y
Description: This routine initializes all input/output devices and
routines. It is normally called as part of the initialization procedure
of a Commodore 64 program cartridge.
EXAMPLE:
JSR IOINIT
B-14. Function Name: LISTEN
Purpose: Command a device on the serial bus to listen
Call Address: $FFB1 (hex) 65457 (decimal)
Communication registers: A
Preparatory routines: None
Error returns: See READST
Stack requirements: None
Registers affected: A
Description: This routine will command a device on the serial bus to
receive data. The accumulator must be loaded with a device number between
0 and 31 before calling the routine. LISTEN will OR the number bit by bit
to convert to a listen address, then transmits this data as a command on
the serial bus. The specified device will then go into listen mode, and
be ready to accept information.
How to Use:
1) Load the accumulator with the number of the device to command
to LISTEN.
2) Call this routine using the JSR instruction.
EXAMPLE:
;COMMAND DEVICE #8 TO LISTEN
LDA #8
JSR LISTEN
BASIC TO MACHINE LANGUAGE 285
~
B-15. Function Name: LOAD
Purpose: Load RAM from device
Call address: $FFD5 (hex) 65493 (decimal)
Communication registers: A, X, Y
Preparatory routines: SETLFS, SETNAM
Error returns: 0,4,5,8,9, READST
Stack requirements: None
Registers affected: A, X, Y
Description: This routine LOADs data bytes from any input device di-
rectly into the memory of the Commodore 64. It can also be used for a
verify operation, comparing data from a device with the data already in
memory, while leaving the data stored in RAM unchanged.
The accumulator (.A) must be set to 0 for a LOAD operation, or 1 for a
verify, If the input device is OPENed with a secondary address (SA) of 0
the header information from the device is ignored. In this case, the X
and Y registers must contain the starting address for the load. If the
device is addressed with a secondary address of 1, then the data is
loaded into memory starting at the location specified by the header. This
routine returns the address of the highest RAM location loaded.
Before this routine can be called, the KERNAL SETLFS, and SETNAM
routines must be called.
+-----------------------------------------------------------------------+
| NOTE: You can NOT LOAD from the keyboard (0), RS-232 (2), or the |
| screen (3). |
+-----------------------------------------------------------------------+
How to Use:
0) Call the SETLFS, and SETNAM routines. If a relocated load is de-
sired, use the SETLFS routine to send a secondary address of 0.
1) Set the A register to 0 for load, 1 for verify.
2) If a relocated load is desired, the X and Y registers must be set
to the start address for the load.
3) Call the routine using the JSR instruction.
286 BASIC TO MACHINE LANGUAGE
~
EXAMPLE:
;LOAD A FILE FROM TAPE
LDA #DEVICE1 ;SET DEVICE NUMBER
LDX #FILENO ;SET LOGICAL FILE NUMBER
LDY CMD1 ;SET SECONDARY ADDRESS
JSR SETLFS
LDA #NAME1-NAME ;LOAD A WITH NUMBER OF
;CHARACTERS IN FILE NAME
LDX #<NAME ;LOAD X AND Y WITH ADDRESS OF
LDY #>NAME ;FILE NAME
JSR SETNAM
LDA #0 ;SET FLAG FOR A LOAD
LDX #$FF ;ALTERNATE START
LDY #$FF
JSR LOAD
STX VARTAB ;END OF LOAD
STY VARTA B+1
JMP START
NAME .BYT 'FILE NAME'
NAME1 ;
B-16. Function Name: MEMBOT
Purpose: Set bottom of memory
Call address: $FF9C (hex) 65436 (decimal)
Communication registers: X, Y
Preparatory routines: None
Error returns: None
Stack requirements: None
Registers affected: X, Y
Description: This routine is used to set the bottom of the memory. If
the accumulator carry bit is set when this routine is called, a pointer
to the lowest byte of RAM is returned in the X and Y registers. On the
unexpanded Commodore 64 the initial value of this pointer is $0800
(2048 in decimal). If the accumulator carry bit is clear (-O) when this
routine is called, the values of the X and Y registers are transferred to
the low and high bytes, respectively, of the pointer to the beginning of
RAM.
BASIC TO MACHINE LANGUAGE 287
~
How to Use:
TO READ THE BOTTOM OF RAM
1) Set the carry.
2) Call this routine.
TO SET THE BOTTOM OF MEMORY
1) Clear the carry.
2) Call this routine.
EXAMPLE:
;MOVE BOTTOM OF MEMORY UP 1 PAGE
SEC ;READ MEMORY BOTTOM
JSR MEMBOT
INY
CLC ;SET MEMORY BOTTOM TO NEW VALUE
JSR MEMBOT
B-17. Function Name: MEMTOP
Purpose: Set the top of RAM
Call address: $FF99 (hex) 65433 (decimal)
Communication registers: X, Y
Preparatory routines: None
Error returns: None
Stack requirements: 2
Registers affected: X, Y
Description: This routine is used to set the top of RAM. When this
routine is called with the carry bit of the accumulator set, the pointer
to the top of RAM will be loaded into the X and Y registers. When this
routine is called with the accumulator carry bit clear, the contents of
the X and Y registers are loaded in the top of memory pointer, changing
the top of memory.
EXAMPLE:
;DEALLOCATE THE RS-232 BUFFER
SEC
JSR MEMTOP ;READ TOP OF MEMORY
DEX
CLC
JSR MEMTOP ;SET NEW TOP OF MEMORY
288 BASIC TO MACHINE LANGUAGE
~
B-18. Function Name: OPEN
Purpose: Open a logical file
Call address: $FFC0 (hex) 65472 (decimal)
Communication registers: None
Preparatory routines: SETLFS, SETNAM
Error returns: 1,2,4,5,6,240, READST
Stack requirements: None
Registers affected: A, X, Y
Description: This routine is used to OPEN a logical file. Once the
logical file is set up, it can be used for input/output operations. Most
of the I/O KERNAL routines call on this routine to create the logical
files to operate on. No arguments need to be set up to use this routine,
but both the SETLFS and SETNAM KERNAL routines must be called before
using this routine.
How to Use:
0) Use the SETLFS routine.
1) Use the SETNAM routine.
2) Call this routine.
EXAMPLE:
This is an implementation of the BASIC statement: OPEN 15,8,15,"I/O"
LDA #NAME2-NAME ;LENGTH OF FILE NAME FOR SETLFS
LDY #>NAME ;ADDRESS OF FILE NAME
LDX #<NAME
JSR SETNAM
LDA #15
LDX #8
LDY #15
JSR SETLFS
JSR OPEN
NAME .BYT 'I/O'
NAME2
BASIC TO MACHINE LANGUAGE 289
~
B-19. Function Name: PLOT
Purpose: Set cursor location
Call address: $FFF0 (hex) 65520 (decimal)
Communication registers: A, X, Y
Preparatory routines: None
Error returns: None
Stack requirements: 2
Registers affected: A, X, Y
Description: A call to this routine with the accumulator carry flag
set loads the current position of the cursor on the screen (in X,Y
coordinates) into the Y and X registers. Y is the column number of the
cursor location (6-39), and X is the row number of the location of the
cursor (0-24). A call with the carry bit clear moves the cursor to X,Y
as determined by the Y and X registers.
How to Use:
READING CURSOR LOCATION
1) Set the carry flag.
2) Call this routine.
3) Get the X and Y position from the Y and X registers, respectively.
SETTING CURSOR LOCATION
1) Clear carry flag.
2) Set the Y and X registers to the desired cursor location.
3) Call this routine.
EXAMPLE:
;MOVE THE CURSOR TO ROW 10, COLUMN 5 (5,10)
LDX #10
LDY #5
CLC
JSR PLOT
290 BASIC TO MACHINE LANGUAGE
~
B.20. Function Name: RAMTAS
Purpose: Perform RAM test
Call address: $FF87 (hex) 65415 (decimal)
Communication registers: A, X, Y
Preparatory routines: None
Error returns: None
Stack requirements: 2
Registers affected: A, X, Y
Description: This routine is used to test RAM and set the top and
bottom of memory pointers accordingly. It also clears locations $0000 to
$0101 and $0200 to $03FF. It also allocates the cassette buffer, and sets
the screen base to $0400. Normally, this routine is called as part of the
initialization process of a Commodore 64 program cartridge.
EXAMPLE:
JSR RAMTAS
B-21. Function Name: RDTIM
Purpose: Read system clock
Call address: $FFDE (hex) 65502 (decimal)
Communication registers: A, X, Y
Preparatory routines: None
Error returns: None
Stack requirements: 2
Registers affected: A, X, Y
Description: This routine is used to read the system clock. The clock's
resolution is a 60th of a second. Three bytes are returned by the
routine. The accumulator contains the most significant byte, the X index
register contains the next most significant byte, and the Y index
register contains the least significant byte.
EXAMPLE:
JSR RDTIM
STY TIME
STX TIME+1
STA TIME+2
...
TIME *=*+3
BASIC TO MACHINE LANGUAGE 291
~
B-22. Function Name: READST
Purpose: Read status word
Call address: $FFB7 (hex) 65463 (decimal)
Communication registers: A
Preparatory routines: None
Error returns: None
Stack requirements: 2
Registers affected: A
Description: This routine returns the current status of the I/O devices
in the accumulator. The routine is usually called after new communication
to an I/O device. The routine gives you information about device status,
or errors that have occurred during the I/O operation.
The bits returned in the accumulator contain the following information:
(see table below)
+---------+------------+---------------+------------+-------------------+
| ST Bit | ST Numeric | Cassette | Serial | Tape Verify |
| Position| Value | Read | Bus R/W | + Load |
+---------+------------+---------------+------------+-------------------+
| 0 | 1 | | time out | |
| | | | write | |
+---------+------------+---------------+------------+-------------------+
| 1 | 2 | | time out | |
| | | | read | |
+---------+------------+---------------+------------+-------------------+
| 2 | 4 | short block | | short block |
+---------+------------+---------------+------------+-------------------+
| 3 | 8 | long block | | long block |
+---------+------------+---------------+------------+-------------------+
| 4 | 16 | unrecoverable | | any mismatch |
| | | read error | | |
+---------+------------+---------------+------------+-------------------+
| 5 | 32 | checksum | | checksum |
| | | error | | error |
+---------+------------+---------------+------------+-------------------+
| 6 | 64 | end of file | EOI line | |
+---------+------------+---------------+------------+-------------------+
| 7 | -128 | end of tape | device not | end of tape |
| | | | present | |
+---------+------------+---------------+------------+-------------------+
292 BASIC TO MACHINE LANGUAGE
~
How to Use:
1) Call this routine.
2) Decode the information in the A register as it refers to your pro-
gram.
EXAMPLE:
;CHECK FOR END OF FILE DURING READ
JSR READST
AND #64 ;CHECK EOF BIT (EOF=END OF FILE)
BNE EOF ;BRANCH ON EOF
B-23. Function Name: RESTOR
Purpose: Restore default system and interrupt vectors
Call address: $FF8A (hex) 65418 (decimal)
Preparatory routines: None
Error returns: None
Stack requirements: 2
Registers affected: A, X, Y
Description: This routine restores the default values of all system
vectors used in KERNAL and BASIC routines and interrupts. (See the Memory
Map for the default vector contents). The KERNAL VECTOR routine is used
to read and alter individual system vectors.
How to Use:
1) Call this routine.
EXAMPLE:
JSR RESTOR
B-24. Function Name: SAVE
Purpose: Save memory to a device
Call address: $FFD8 (hex) 65496 (decimal)
Communication registers: A, X, Y
Preparatory routines: SETLFS, SETNAM
Error returns: 5,8,9, READST
Stack requirements: None
Registers affected: A, X, Y
BASIC TO MACHINE LANGUAGE 293
~
Description: This routine saves a section of memory. Memory is saved
from an indirect address on page 0 specified by the accumulator to the
address stored in the X and Y registers. It is then sent to a logical
file on an input/output device. The SETLFS and SETNAM routines must be
used before calling this routine. However, a file name is not required to
SAVE to device 1 (the Datassette(TM) recorder). Any attempt to save to
other devices without using a file name results in an error.
+-----------------------------------------------------------------------+
| NOTE: Device 0 (the keyboard), device 2 (RS-232), and device 3 (the |
| screen) cannot be SAVEd to. If the attempt is made, an error occurs, |
| and the SAVE is stopped. |
+-----------------------------------------------------------------------+
How to Use:
0) Use the SETLFS routine and the SETNAM routine (unless a SAVE with no
file name is desired on "a save to the tape recorder"),
1) Load two consecutive locations on page 0 with a pointer to the start
of your save (in standard 6502 low byte first, high byte next
format).
2) Load the accumulator with the single byte page zero offset to the
pointer.
3) Load the X and Y registers with the low byte and high byte re-
spectively of the location of the end of the save.
4) Call this routine.
EXAMPLE:
LDA #1 ;DEVICE = 1:CASSETTE
JSR SETLFS
LDA #0 ;NO FILE NAME
JSR SETNAM
LDA PROG ;LOAD START ADDRESS OF SAVE
STA TXTTAB ;(LOW BYTE)
LDA PROG+1
STA TXTTA B+1 ;(HIGH BYTE)
LDX VARTAB ;LOAD X WITH LOW BYTE OF END OF SAVE
LDY VARTAB+1 ;LOAD Y WITH HIGH BYTE
LDA #<TXTTAB ;LOAD ACCUMULATOR WITH PAGE 0 OFFSET
JSR SAVE
294 BASIC TO MACHINE LANGUAGE
~
B-25. Function Name: SCNKEY
Purpose: Scan the keyboard
Call address: $FF9F (hex) 65439 (decimal)
Communication registers: None
Preparatory routines: IOINIT
Error returns: None
Stack requirements: 5
Registers affected: A, X, Y
Description: This routine scans the Commodore 64 keyboard and checks
for pressed keys. It is the same routine called by the interrupt handler.
If a key is down, its ASCII value is placed in the keyboard queue. This
routine is called only if the normal IRQ interrupt is bypassed.
How to Use:
1) Call this routine.
EXAMPLE:
GET JSR SCNKEY ;SCAN KEYBOARD
JSR GETIN ;GET CHARACTER
CMP #0 ;IS IT NULL?
BEQ GET ;YES... SCAN AGAIN
JSR CHROUT ;PRINT IT
B-26. Function Name: SCREEN
Purpose: Return screen format
Call address: $FFED (hex) 65517 (decimal)
Communication registers: X, Y
Preparatory routines: None
Stack requirements: 2
Registers affected: X, Y
Description: This routine returns the format of the screen, e.g., 40
columns in X and 25 lines in Y. The routine can be used to determine what
machine a program is running on. This function has been implemented on
the Commodore 64 to help upward compatibility of your programs.
BASIC TO MACHINE LANGUAGE 295
~
How to Use:
1) Call this routine.
EXAMPLE:
JSR SCREEN
STX MAXCOL
STY MAXROW
B-27. Function Name: SECOND
Purpose: Send secondary address for LISTEN
Call address: $FF93 (hex) 65427 (decimal)
Communication registers: A
Preparatory routines: LISTEN
Error returns: See READST
Stack requirements: 8
Registers affected: A
Description: This routine is used to send a secondary address to an
I/O device after a call to the LISTEN routine is made, and the device is
commanded to LISTEN. The routine canNOT be used to send a secondary
address after a call to the TALK routine.
A secondary address is usually used to give setup information to a
device before I/O operations begin.
When a secondary address is to be sent to a device on the serial bus,
the address must first be ORed with $60.
How to Use:
1) load the accumulator with the secondary address to be sent.
2) Call this routine.
EXAMPLE:
;ADDRESS DEVICE #8 WITH COMMAND (SECONDARY ADDRESS) #15
LDA #8
JSR LISTEN
LDA #15
JSR SECOND
296 BASIC TO MACHINE LANGUAGE
~
B-28. Function Name: SETLFS
Purpose: Set up a logical file
Call address: $FFBA (hex) 65466 (decimal)
Communication registers: A, X, Y
Preparatory routines: None
Error returns: None
Stack requirements: 2
Registers affected: None
Description: This routine sets the logical file number, device address,
and secondary address (command number) for other KERNAL routines.
The logical file number is used by the system as a key to the file
table created by the OPEN file routine. Device addresses can range from 0
to 31. The following codes are used by the Commodore 64 to stand for the
CBM devices listed below:
ADDRESS DEVICE
0 Keyboard
1 Datassette(TM)
2 RS-232C device
3 CRT display
4 Serial bus printer
8 CBM serial bus disk drive
Device numbers 4 or greater automatically refer to devices on the
serial bus.
A command to the device is sent as a secondary address on the serial
bus after the device number is sent during the serial attention
handshaking sequence. If no secondary address is to be sent, the Y index
register should be set to 255.
How to Use:
1) Load the accumulator with the logical file number.
2) Load the X index register with the device number.
3) Load the Y index register with the command.
BASIC TO MACHINE LANGUAGE 297
~
EXAMPLE:
FOR LOGICAL FILE 32, DEVICE #4, AND NO COMMAND:
LDA #32
LDX #4
LDY #255
JSR SETLFS
B-29. Function Name: SETMSG
Purpose: Control system message output
Call address: $FF90 (hex) 65424 (decimal)
Communication registers: A
Preparatory routines: None
Error returns: None
Stack requirements: 2
Registers affected: A
Description: This routine controls the printing of error and control
messages by the KERNAL. Either print error messages or print control mes-
sages can be selected by setting the accumulator when the routine is
called. FILE NOT FOUND is an example of an error message. PRESS PLAY ON
CASSETTE is an example of a control message.
Bits 6 and 7 of this value determine where the message will come from.
If bit 7 is 1, one of the error messages from the KERNAL is printed. If
bit 6 is set, control messages are printed.
How to Use:
1) Set accumulator to desired value.
2) Call this routine.
EXAMPLE:
LDA #$40
JSR SETMSG ;TURN ON CONTROL MESSAGES
LDA #$80
JSR SETMSG ;TURN ON ERROR MESSAGES
LDA #0
JSR SETMSG ;TURN OFF ALL KERNAL MESSAGES
298 BASIC TO MACHINE LANGUAGE
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B-30. Function Name: SETNAM
Purpose: Set file name
Call address: $FFBD (hex) 65469 (decimal)
Communication registers: A, X, Y
Preparatory routines:
Stack requirements: 2
Registers affected:
Description: This routine is used to set up the file name for the OPEN,
SAVE, or LOAD routines. The accumulator must be loaded with the length of
the file name. The X and Y registers must be loaded with the address of
the file name, in standard 6502 low-byte/high-byte format. The address
can be any valid memory address in the system where a string of
characters for the file name is stored. If no file name is desired, the
accumulator must be set to 0, representing a zero file length. The X and
Y registers can be set to any memory address in that case.
How to Use:
1) Load the accumulator with the length of the file name.
2) Load the X index register with the low order address of the file
name.
3) Load the Y index register with the high order address.
4) Call this routine.
EXAMPLE:
LDA #NAME2-NAME ;LOAD LENGTH OF FILE NAME
LDX #<NAME ;LOAD ADDRESS OF FILE NAME
LDY #>NAME
JSR SETNAM
B-31. Function Name: SETTIM
Purpose: Set the system clock
Call address: $FFDB (hex) 65499 (decimal)
Communication registers: A, X, Y
Preparatory routines: None
Error returns: None
Stack requirements: 2
Registers affected: None
BASIC TO MACHINE LANGUAGE 299
~
Description: A system clock is maintained by an interrupt routine that
updates the clock every 1/60th of a second (one "jiffy"). The clock is
three bytes long, which gives it the capability to count up to 5,184,000
jiffies (24 hours). At that point the clock resets to zero. Before
calling this routine to set the clock, the accumulator must contain the
most significant byte, the X index register the next most significant
byte, and the Y index register the least significant byte of the initial
time setting (in jiffies).
How to Use:
1) Load the accumulator with the MSB of the 3-byte number to set the
clock.
2) Load the X register with the next byte.
3) Load the Y register with the LSB.
4) Call this routine.
EXAMPLE:
;SET THE CLOCK TO 10 MINUTES = 3600 JIFFIES
LDA #0 ;MOST SIGNIFICANT
LDX #>3600
LDY #<3600 ;LEAST SIGNIFICANT
JSR SETTIM
B-32. Function Name: SETTMO
Purpose: Set IEEE bus card timeout flag
Call address: $FFA2 (hex) 65442 (decimal)
Communication registers: A
Preparatory routines: None
Error returns: None
Stack requirements: 2
Registers affected: None
+-----------------------------------------------------------------------+
| NOTE: This routine is used ONLY with an IEEE add-on card! |
+-----------------------------------------------------------------------+
Description: This routine sets the timeout flag for the IEEE bus. When
the timeout flag is set, the Commodore 64 will wait for a device on the
IEEE port for 64 milliseconds. If the device does not respond to the
Commodore 64's Data Address Valid (DAV) signal within that time the
Commodore 64 will recognize an error condition and leave the handshake
sequence. When this routine is called when the accumulator contains a 0
in bit 7, timeouts are enabled. A 1 in bit 7 will disable the timeouts.
300 BASIC TO MACHINE LANGUAGE
~
+-----------------------------------------------------------------------+
| NOTE: The Commodore 64 uses the timeout feature to communicate that a |
| disk file is not found on an attempt to OPEN a file only with an IEEE |
| card. |
+-----------------------------------------------------------------------+
How to Use:
TO SET THE TIMEOUT FLAG
1) Set bit 7 of the accumulator to 0.
2) Call this routine.
TO RESET THE TIMEOUT FLAG
1) Set bit 7 of the accumulator to 1.
2) Call this routine.
EXAMPLE:
;DISABLE TIMEOUT
LDA #0
JSR SETTMO
B-33. Function Name: STOP
Purpose: Check if <STOP> key is pressed
Call address: $FFE1 (hex) 65505 (decimal)
Communication registers: A
Preparatory routines: None
Error returns: None
Stack requirements: None
Registers affected: A, X
Description: If the <STOP> key on the keyboard was pressed during a
UDTIM call, this call returns the Z flag set. In addition, the channels
will be reset to default values. All other flags remain unchanged. If the
<STOP> key is not pressed then the accumulator will contain a byte
representing the lost row of the keyboard scan. The user can also check
for certain other keys this way.
How to Use:
0) UDTIM should be called before this routine.
1) Call this routine.
2) Test for the zero flag.
BASIC TO MACHINE LANGUAGE 301
~
EXAMPLE:
JSR UDTIM ;SCAN FOR STOP
JSR STOP
BNE *+5 ;KEY NOT DOWN
JMP READY ;=... STOP
B-34. Function Name: TALK
Purpose: Command a device on the serial bus to TALK
Call address: $FFB4 (hex) 65460 (decimal)
Communication registers: A
Preparatory routines: None
Error returns: See READST
Stack requirements: 8
Registers affected: A
Description: To use this routine the accumulator must first be loaded
with a device number between 0 and 31. When called, this routine then
ORs bit by bit to convert this device number to a talk address. Then this
data is transmitted as a command on the serial bus.
How to Use:
1) Load the accumulator with the device number.
2) Call this routine.
EXAMPLE:
;COMMAND DEVICE #4 TO TALK
LDA #4
JSR TALK
B-35. Function Name: TKSA
Purpose: Send a secondary address to a device commanded to TALK
Call address: $FF96 (hex) 65430 (decimal)
Communication registers: A
Preparatory routines: TALK
Error returns: See READST
Stack requirements: 8
Registers affected: A
302 BASIC TO MACHINE LANGUAGE
~
Description: This routine transmits a secondary address on the serial
bus for a TALK device. This routine must be called with a number between
0 and 31 in the accumulator. The routine sends this number as a secondary
address command over the serial bus. This routine can only be called
after a call to the TALK routine. It will not work after a LISTEN.
How to Use:
0) Use the TALK routine.
1) Load the accumulator with the secondary address.
2) Call this routine.
EXAMPLE:
;TELL DEVICE #4 TO TALK WITH COMMAND #7
LDA #4
JSR TALK
LDA #7
JSR TALKSA
B-36. Function Name: UDTIM
Purpose: Update the system clock
Call address: $FFEA (hex) 65514 (decimal)
Communication registers: None
Preparatory routines: None
Error returns: None
Stack requirements: 2
Registers affected: A, X
Description: This routine updates the system clock. Normally this
routine is called by the normal KERNAL interrupt routine every 1/60th of
a second. If the user program processes its own interrupts this routine
must be called to update the time. In addition, the <STOP> key routine
must be called, if the <STOP> key is to remain functional.
How to Use:
1) Call this routine.
EXAMPLE:
JSR UDTIM
BASIC TO MACHINE LANGUAGE 303
~
B-37. Function Name: UNLSN
Purpose: Send an UNLISTEN command
Call address: $FFAE (hex) 65454 (decimal)
Communication registers: None
Preparatory routines: None
Error returns: See READST
Stack requirements: 8
Registers affected: A
Description: This routine commands all devices on the serial bus to
stop receiving data from the Commodore 64 (i.e., UNLISTEN). Calling this
routine results in an UNLISTEN command being transmitted on the serial
bus. Only devices previously commanded to listen are affected. This
routine is normally used after the Commodore 64 is finished sending data
to external devices. Sending the UNLISTEN commands the listening devices
to get off the serial bus so it can be used for other purposes.
How to Use:
1) Call this routine.
EXAMPLE:
JSR UNLSN
B-38. Function Name: UNTLK
Purpose: Send an UNTALK command
Call address: $FFAB (hex) 65451 (decimal)
Communication registers: None
Preparatory routines: None
Error returns: See READST
Stack requirements: 8
Registers affected: A
Description: This routine transmits an UNTALK command on the serial
bus. All devices previously set to TALK will stop sending data when this
command is received.
How to Use:
1) Call this routine.
304 BASIC TO MACHINE LANGUAGE
~
EXAMPLE:
JSR UNTALK
B-39. Function Name: VECTOR
Purpose: Manage RAM vectors
Call address: $FF8D (hex) 65421 (decimal)
Communication registers: X, Y
Preparatory routines: None
Error returns: None
Stack requirements: 2
Registers affected: A, X, Y
Description: This routine manages all system vector jump addresses
stored in RAM. Calling this routine with the the accumulator carry bit
set stores the current contents of the RAM vectors in a list pointed to
by the X and Y registers. When this routine is called with the carry
clear, the user list pointed to by the X and Y registers is transferred
to the system RAM vectors. The RAM vectors are listed in the memory map.
+-----------------------------------------------------------------------+
| NOTE: This routine requires caution in its use. The best way to use it|
| is to first read the entire vector contents into the user area, alter |
| the desired vectors, and then copy the contents back to the system |
| vectors. |
+-----------------------------------------------------------------------+
How to Use:
READ THE SYSTEM RAM VECTORS
1) Set the carry.
2) Set the X and y registers to the address to put the vectors.
3) Call this routine.
LOAD THE SYSTEM RAM VECTORS
1) Clear the carry bit.
2) Set the X and Y registers to the address of the vector list in RAM
that must be loaded.
3) Call this routine.
BASIC TO MACHINE LANGUAGE 305
~
EXAMPLE:
;CHANGE THE INPUT ROUTINES TO NEW SYSTEM
LDX #<USER
LDY #>USER
SEC
JSR VECTOR ;READ OLD VECTORS
LDA #<MYINP ;CHANGE INPUT
STA USER+10
LDA #>MYINP
STA USER+11
LDX #<USER
LDY #>USER
CLC
JSR VECTOR ;ALTER SYSTEM
...
USER *=*+26
ERROR CODES
The following is a list of error messages which can occur when using
the KERNAL routines. If an error occurs during a KERNAL routine , the
carry bit of the accumulator is set, and the number of the error message
is returned in the accumulator.
+-----------------------------------------------------------------------+
| NOTE: Some KERNAL I/O routines do not use these codes for error |
| messages. Instead, errors are identified using the KERNAL READST |
| routine. |
+-----------------------------------------------------------------------+
+-------+---------------------------------------------------------------+
| NUMBER| MEANING |
+-------+---------------------------------------------------------------+
| 0 | Routine terminated by the <STOP> key |
| 1 | Too many open files |
| 2 | File already open |
| 3 | File not open |
| 4 | File not found |
| 5 | Device not present |
| 6 | File is not an input file |
| 7 | File is not an output file |
| 8 | File name is missing |
| 9 | Illegal device number |
| 240 | Top-of-memory change RS-232 buffer allocation/deallocation |
+-------+---------------------------------------------------------------+
306 BASIC TO MACHINE LANGUAGE
~
USING MACHINE LANGUAGE FROM BASIC
There are several methods of using BASIC and machine language on the
Commodore 64, including special statements as part of CBM BASIC as well
as key locations in the machine. There are five main ways to use machine
language routines from BASIC on the Commodore 64. They are:
1) The BASIC SYS statement
2) The BASIC USR function
3) Changing one of the RAM I/O vectors
4) Changing one of the RAM interrupt vectors
5) Changing the CHRGET routine
1) The BASIC statement SYS X causes a JUMP to a machine language
subroutine located at address X. The routine must end with an RTS
(ReTurn from Subroutine) instruction. This will transfer control
back to BASIC.
Parameters are generally passed between the machine language
routine and the BASIC program using the BASIC PEEK and POKE
statements, and their machine language equivalents.
The SYS command is the most useful method of combining BASIC with
machine language. PEEKs and POKEs make multiple parameter passing
easy. There can be many SYS statements in a program, each to a
different (or even the same) machine language routine.
2) The BASIC function USR(X) transfers control to the machine language
subroutine located at the address stored in locations 785 and 786.
(The address is stored in standard low-byte/high-byte format.) The
value X is evaluated and passed to the machine language subroutine
through floating point accumulator #1, located beginning at address
$61 (see memory map for more details). A value may be returned back
to the BASIC program by placing it in the floating point
accumulator. The machine language routine must end with an RTS
instruction to return to BASIC.
This statement is different from the SYS, because you have to set
up an indirect vector. Also different is the format through which
the variable is passed (floating point format). The indirect vector
must be changed if more than one machine language routine is used.
BASIC TO MACHINE LANGUAGE 307
~
3) Any of the inpUt/OUtPUT or BASIC internal routines accessed through
the vector table located on page 3 (see ADDRESSING MODES, ZERO PAGE)
can be replaced, or amended by user code. Each 2-byte vector
consists of a low byte and a high byte address which is used by the
operating system.
The KERNAL VECTOR routine is the most reliable way to change any
of the vectors, but a single vector can be changed by POKES. A new
vector will point to a user prepared routine which is meant to
replace or augment the standard system routine. When the appropriate
BASIC command is executed, the user routine will be executed. If
after executing the user routine, it is necessary to execute the
normal system routine, the user program must JMP (JUMP) to the
address formerly contained in the vector. If not, the routine must
end with a RTS to transfer control back to BASIC.
4) The HARDWARE INTERRUPT (IRQ) VECTOR can be changed. Every 1/60th of
a second, the operating system transfers control to the routine
specified by this vector. The KERNAL normally uses this for timing,
keyboard scanning, etc. If this technique is used, you should always
transfer control to the normal IRQ handling routine, unless the
replacement routine is prepared to handle the CIA chip. (REMEMBER to
end the routine with an RTI (ReTurn from Interrupt) if the CIA is
handled by the routine).
This method is useful for tasks which must happen concurrently
with a BASIC program, but has the drawback of being more difficult.
+-----------------------------------------------------------------------+
| NOTE: ALWAYS DISABLE INTERRUPTS BEFORE CHANGING THIS VECTOR! |
+-----------------------------------------------------------------------+
5) The CHRGET routine is used by BASIC to get each character/token.
This makes it simple to add new BASIC commands. Naturally, each new
command must be executed by a user written machine language
subroutine. A common way to use this method is to specify a
character (@ for example) which will occur before any of the new
commands. The new CHRGET routine will search for the special
character. If none is present, control is passed to the normal BASIC
CHRGET routine. If the special character is present, the new command
is interpreted and executed by your machine language program. This
minimizes the extra execution time added by the need to search for
additional commands. This technique is often called a wedge.
308 BASIC TO MACHINE LANGUAGE
~
WHERE TO PUT MACHINE LANGUAGE ROUTINES
The best place for machine language routines on the Commodore 64 is
from $C000-$CFFF, assuming the routines are smaller than 4K bytes long.
This section of memory is not disturbed by BASIC.
If for some reason it's not possible or desirable to put the machine
language routine at $C000, for instance if the routine is larger than 4K
bytes, it then becomes necessary to reserve an area at the top of memory
from BASIC for the routine. The top of memory is normally $9FFF. The top
of memory can be changed through the KERNAL routine MEMTOP, or by the
following BASIC statements:
10 POKE51,L:POKE52,H:POKE55,1:POKE56,H:CLR
Where H and L are the high and low portions, respectively, of the new
top of memory. For example, to reserve the area from $9000 to $9FFF for
machine language, use the following:
10 POKE5110:POKE52,144:POKE5510:POKE56,144:CLR
HOW TO ENTER MACHINE LANGUAGE
There are 3 common methods to add the machine language programs to a
BASIC program. They are:
1) DATA STATEMENTS:
By READing DATA statements, and POKEing the values into memory at the
start of the program, machine language routines can be added. This is the
easiest method. No special methods are needed to save the two parts of
the program, and it is fairly easy to debug. The drawbacks include taking
up more memory space, and the wait while the program is POKED in.
Therefore, this method is better for smaller routines.
EXAMPLE:
10 RESTORE:FORX=1T09:READA:POKE12*4096+X,A:NEXT
.
BASIC PROGRAM
.
1000 DATA 161,1,204,204,204,204,204,204,96
BASIC TO MACHINE LANGUAGE 309
~
2) MACHINE LANGUAGE MONITOR (64MON):
This program allows you to enter a program in either HEX or SYMBOLIC
codes, and save the portion of memory the program is in. Advantages of
this method include easier entry of the machine language routines,
debugging aids, and a much faster means of saving and loading. The
drawback to this method is that it generally requires the BASIC program
to load the machine language routine from tape or disk when it is
started. (For more details on 64MON see the machine language section.)
EXAMPLE:
The following is an example of a BASIC program using a machine language
routine prepared by 64MON. The routine is stored on tape:
10 IF FLAG=L THEN 20
15 FLAG=1:LOAD"MACHINE LANGUAGE ROUTINE NAME",1,1
20
.
.
REST OF BASIC PROGRAM
3) EDITOR/ASSEMBLER PACKAGE:
Advantages are similar to using a machine language monitor, but
programs are even easier to enter. Disadvantages are also similar to the
use of a machine language monitor.
COMMODORE 64 MEMORY MAP
HEX DECIMAL
LABEL ADDRESS LOCATION DESCRIPTION
-------------------------------------------------------------------------
D6510 0000 0 6510 On-Chip Data-Direction Register
R6510 0001 1 6510 On-Chip 8-Bit Input/Output Register
0002 2 Unused
ADRAY1 0003-0004 3-4 Jump Vector: Convert Floating-Integer
310 BASIC TO MACHINE LANGUAGE
~
HEX DECIMAL
LABEL ADDRESS LOCATION DESCRIPTION
-------------------------------------------------------------------------
ADRAY2 0005-0006 5-6 Jump Vector: Convert Integer--Floating
CHARAC 0007 7 Search Character
ENDCHR 0008 8 Flag: Scan for Quote at End of String
TRMPOS 0009 9 Screen Column From Last TAB
VERCK 000A 10 Flag: 0 = Load, 1 = Verify
COUNT 000B 11 Input Buffer Pointer / No. of Subscripts
DIMFLG 000C 12 Flag: Default Array DiMension
VALTYP 000D 13 Data Type: $FF = String, $00 = Numeric
INTFLG 000E 14 Data Type: $80 = Integer, $00 = Floating
GARBFL 000F 15 Flag: DATA scan/LIST quote/Garbage Coll
SUBFLG 0010 16 Flag: Subscript Ref / User Function Call
INPFLG 0011 17 Flag: $00 = INPUT, $40 = GET, $98 = READ
TANSGN 0012 18 Flag TAN sign / Comparison Result
0013 19 Flag: INPUT Prompt
LINNUM 0014-0015 20-21 Temp: Integer Value
TEMPPT 0016 22 Pointer Temporary String
LASTPT 0017-0018 23-24 Last Temp String Address
TEMPST 0019-0021 25-33 Stack for Temporary Strings
INDEX 0022-0025 34-37 Utility Pointer Area
INDEX1 0022-0023 34-35 First Utility Pointer.
INDEX2 0024-0025 36-37 Second Utility Pointer.
RESHO 0026-002A 38-42 Floating-Point Product of Multiply
TXTTAB 002B-002C 43-44 Pointer: Start of BASIC Text
VARTAB 002D-002E 45-46 Pointer: Start of BASIC Variables
ARYTAB 002F-0030 47-48 Pointer: Start of BASIC Arrays
STREND 0031-0032 49-50 Pointer End of BASIC Arrays (+1)
FRETOP 0033-0034 51-52 Pointer: Bottom of String Storage
FRESPC 0035-0036 53-54 Utility String Pointer
MEMSIZ 0037-0038 55-56 Pointer: Highest Address Used by BASIC
CURLIN 0039-003A 57-58 Current BASIC Line Number
OLDLIN 003B-003C 59-60 Previous BASIC Line Number
OLDTXT 003D-003E 61-62 Pointer: BASIC Statement for CONT
DATLIN 003F-0040 63-64 Current DATA Line Number
DATPTR 0041-0042 65-66 Pointer: Current DATA Item Address
INPPTR 0043-0044 67-68 Vector: INPUT Routine
VARNAM 0045-0046 69-70 Current BASIC Variable Name
BASIC TO MACHINE LANGUAGE 311
~
HEX DECIMAL
LABEL ADDRESS LOCATION DESCRIPTION
-------------------------------------------------------------------------
VARPNT 0047-0048 71-72 Pointer: Current BASIC Variable Data
FORPNT 0049-004A 73-74 Pointer: Index Variable for FOR/NEXT
004B-0060 75-96 Temp Pointer / Data Area
VARTXT 004B-004C 75-76 Temporary storage for TXTPTR during
READ, INPUT and GET.
OPMASK 004D 77 Mask used during FRMEVL.
TEMPF3 004E-0052 78-82 Temporary storage for FLPT value.
FOUR6 0053 83 Length of String Variable during Garbage
collection.
JMPER 0054-0056 84-86 Jump Vector used in Function Evaluation-
JMP followed by Address ($4C,$LB,$MB).
TEMPF1 0057-005B 87-91 Temporary storage for FLPT value.
TEMPF2 005C-0060 92-96 Temporary storage for FLPT value.
FACEXP 0061 97 Floating-Point Accumulator #1: Exponent
FACHO 0062-0065 98-101 Floating Accum. #1: Mantissa
FACSGN 0066 102 Floating Accum. #1: Sign
SGNFLG 0067 103 Pointer: Series Evaluation Constant
BITS 0068 104 Floating Accum. #1: Overflow Digit
ARGEXP 0069 105 Floating-Point Accumulator #2: Exponent
ARGHO 006A-006D 106-109 Floating Accum. #2: Mantissa
ARGSGN 006E 110 Floating Accum. #2: Sign
ARISGN 006F 111 Sign Comparison Result: Accum. # 1 vs #2
FACOV 0070 112 Floating Accum. #1. Low-Order (Rounding)
FBUFPT 0071-0072 113-114 Pointer: Cassette Buffer
CHRGET 0073-008A 115-138 Subroutine: Get Next Byte of BASIC Text
CHRGOT 0079 121 Entry to Get Same Byte of Text Again
TXTPTR 007A-007B 122-123 Pointer: Current Byte of BASIC Text
RNDX 008B-008F 139-143 Floating RND Function Seed Value
STATUS 0090 144 Kernal I/O Status Word: ST
STKEY 0091 145 Flag: STOP key / RVS key
SVXT 0092 146 Timing Constant for Tape
VERCK 0093 147 Flag: 0 = Load, 1 = Verify
C3PO 0094 148 Flag: Serial Bus-Output Char. Buffered
BSOUR 0095 149 Buffered Character for Serial Bus
SYNO 0096 150 Cassette Sync No.
312 BASIC TO MACHINE LANGUAGE
~
HEX DECIMAL
LABEL ADDRESS LOCATION DESCRIPTION
-------------------------------------------------------------------------
0097 151 Temp Data Area
LDTND 0098 152 No. of Open Files / Index to File Table
DFLTN 0099 153 Default Input Device (0)
DFLTO 009A 154 Default Output (CMD) Device (3)
PRTY 009B 155 Tape Character Parity
DPSW 009C 156 Flag: Tape Byte-Received
MSGFLG 009D 157 Flag: $80 = Direct Mode, $00 = Program
PTR1 009E 158 Tape Pass 1 Error Log
PTR2 009F 159 Tape Pass 2 Error Log
TIME 00A0-00A2 160-162 Real-Time Jiffy Clock (approx) 1/60 Sec
00A3-00A4 163-164 Temp Data Area
CNTDN 00A5 165 Cassette Sync Countdown
BUFPNT 00A6 166 Pointer: Tape I/O Buffer
INBIT 00A7 167 RS-232 Input Bits / Cassette Temp
BITCI 00A8 168 RS-232 Input Bit Count / Cassette Temp
RINONE 00A9 169 RS-232 Flag: Check for Start Bit
RIDATA 00AA 170 RS-232 Input Byte Buffer/Cassette Temp
RIPRTY 00AB 171 RS-232 Input Parity / Cassette Short Cnt
SAL 00AC-00AD 172-173 Pointer: Tape Buffer/ Screen Scrolling
EAL 00AE-00AF 174-175 Tape End Addresses/End of Program
CMP0 00B0-00B1 176-177 Tape Timing Constants
TAPE1 00B2-00B3 178-179 Pointer: Start of Tape Buffer
BITTS 00B4 180 RS-232 Out Bit Count / Cassette Temp
NXTBIT 00B5 181 RS-232 Next Bit to Send/ Tape EOT Flag
RODATA 00B6 182 RS-232 Out Byte Buffer
FNLEN 00B7 183 Length of Current File Name
LA 00B8 184 Current Logical File Number
SA 00B9 185 Current Secondary Address
FA 00BA 186 Current Device Number
FNADR 00BB-00BC 187-188 Pointer: Current File Name
ROPRTY 00BD 189 RS-232 Out Parity / Cassette Temp
FSBLK 00BE 190 Cassette Read / Write Block Count
MYCH 00BF 191 Serial Word Buffer
CAS1 00C0 192 Tape Motor Interlock
STAL 00C1-00C2 193-194 I/O Start Address
MEMUSS 00C3-00C4 195-196 Tape Load Temps
LSTX 00C5 197 Current Key Pressed: CHR$(n) 0 = No Key
NDX 00C6 198 No. of Chars. in Keyboard Buffer (Queue)
BASIC TO MACHINE LANGUAGE 313
~
HEX DECIMAL
LABEL ADDRESS LOCATION DESCRIPTION
-------------------------------------------------------------------------
RVS 00C7 199 Flag: Reverse Chars. - 1=Yes, 0=No Used
INDX 00C8 200 Pointer: End of Logical Line for INPUT
LXSP 00C9-00CA 201-202 Cursor X-Y Pos. at Start of INPUT
SFDX 00CB 203 Flag: Print Shifted Chars.
BLNSW 00CC 204 Cursor Blink enable: 0 = Flash Cursor
BLNCT 00CD 205 Timer: Countdown to Toggle Cursor
GDBLN 00CE 206 Character Under Cursor
BLNON 00CF 207 Flag: Last Cursor Blink On/Off
CRSW 00D0 208 Flag: INPUT or GET from Keyboard
PNT 00D1-00D2 209-210 Pointer: Current Screen Line Address
PNTR 00D3 211 Cursor Column on Current Line
QTSW 00D4 212 Flag: Editor in Quote Mode, $00 = NO
LNMX 00D5 213 Physical Screen Line Length
TBLX 00D6 214 Current Cursor Physical Line Number
00D7 215 Temp Data Area
INSRT 00D8 216 Flag: Insert Mode, >0 = # INSTs
LDTB1 00D9-00F2 217-242 Screen Line Link Table / Editor Temps
USER 00F3-00F4 243-244 Pointer: Current Screen Color RAM loc.
KEYTAB 00F5-00F6 245-246 Vector Keyboard Decode Table
RIBUF 00F7-00F8 247-248 RS-232 Input Buffer Pointer
ROBUF 00F9-00FA 249-250 RS-232 Output Buffer Pointer
FREKZP 00FB-00FE 251-254 Free 0-Page Space for User Programs
BASZPT 00FF 255 BASIC Temp Data Area
0100-01FF 256-511 Micro-Processor System Stack Area
0100-010A 256-266 Floating to String Work Area
BAD 0100-013E 256-318 Tape Input Error Log
BUF 0200-02S8 512-600 System INPUT Buffer
LAT 0259-0262 601-610 KERNAL Table: Active Logical File No's.
FAT 0263-026C 611-620 KERNAL Table: Device No. for Each File
SAT 026D-0276 621-630 KERNAL Table: Second Address Each File
KEYD 0277-0280 631-640 Keyboard Buffer Queue (FIFO)
MEMSTR 0281-0282 641-642 Pointer: Bottom of Memory for O.S.
MEMSIZ 0283-0284 643-644 Pointer: Top of Memory for O.S.
TIMOUT 0285 645 Flag: Kernal Variable for IEEE Timeout
COLOR 0286 646 Current Character Color Code
GDCOL 0287 647 Background Color Under Cursor
314 BASIC TO MACHINE LANGUAGE
~
HEX DECIMAL
LABEL ADDRESS LOCATION DESCRIPTION
-------------------------------------------------------------------------
HIBASE 0288 648 Top of Screen Memory (Page)
XMAX 0289 649 Size of Keyboard Buffer
RPTFLG 028A 650 Flag: REPEAT Key Used, $80 = Repeat
KOUNT 028B 651 Repeat Speed Counter
DELAY 028C 652 Repeat Delay Counter
SHFLAG 028D 653 Flag: Keyboard SHIFT Key/CTRL Key/C= Key
LSTSHF 028E 654 Last Keyboard Shift Pattern
KEYLOG 028F-0290 655-656 Vector: Keyboard Table Setup
MODE 0291 657 Flag: $00=Disable SHIFT Keys, $80=Enable
AUTODN 0292 658 Flag: Auto Scroll Down, 0 = ON
M51CTR 0293 659 RS-232: 6551 Control Register Image
MS1CDR 0294 660 RS-232: 6551 Command Register Image
M51AJB 0295-0296 661-662 RS-232 Non-Standard BPS (Time/2-100) USA
RSSTAT 0297 663 RS-232: 6551 Status Register Image
BITNUM 0298 664 RS-232 Number of Bits Left to Send
BAUDOF 0299-029A 665-666 RS-232 Baud Rate: Full Bit Time (us)
RIDBE 029B 667 RS-232 Index to End of Input Buffer
RIDBS 029C 668 RS-232 Start of Input Buffer (Page)
RODBS 029D 669 RS-232 Start of Output Buffer (Page)
RODBE 029E 670 RS-232 Index to End of Output Buffer
IRQTMP 029F-02A0 671-672 Holds IRQ Vector During Tape I/O
ENABL 02A1 673 RS-232 Enables
02A2 674 TOD Sense During Cassette I/O
02A3 675 Temp Storage For Cassette Read
02A4 676 Temp D1 IRQ Indicator For Cassette Read
02A5 677 Temp For Line Index
02A6 678 PAL/NTSC Flag, 0= NTSC, 1 = PAL
02A7-02FF 679-767 Unused
IERROR 0300-0301 768-769 Vector: Print BASIC Error Message
IMAIN 0302-0303 770-771 Vector: BASIC Warm Start
ICRNCH 0304-0305 772-773 Vector: Tokenize BASIC Text
IQPLOP 0306-0307 774-775 Vector: BASIC Text LIST
IGONE 0308-0309 776-777 Vector: BASIC Char. Dispatch
IEVAL 030A-030B 778-779 Vector: BASIC Token Evaluation
SAREG 030C 780 Storage for 6502 .A Register
SXREG 030D 781 Storage for 5502 .X Register
SYREG 030E 782 Storage for 6502 .Y Register
SPREG 030F 783 Storage for 6502 .SP Register
BASIC TO MACHINE LANGUAGE 315
~
HEX DECIMAL
LABEL ADDRESS LOCATION DESCRIPTION
-------------------------------------------------------------------------
USRPOK 0310 784 USR Function Jump Instr (4C)
USRADD 0311-0312 785-786 USR Address Low Byte / High Byte
0313 787 Unused
CINV 0314-0315 788-789 Vector: Hardware Interrupt
CBINV 0316-0317 790-791 Vector: BRK Instr. Interrupt
NMINV 0318-0319 792-793 Vector: Non-Maskable Interrupt
IOPEN 031A-031B 794-795 KERNAL OPEN Routine Vector
ICLOSE 031C-031D 796-797 KERNAL CLOSE Routine Vector
ICHKIN 031E-031F 798-799 KERNAL CHKIN Routine
ICKOUT 0320-0321 800-801 KERNAL CHKOUT Routine
ICLRCH 0322-0323 802-803 KERNAL CLRCHN Routine Vector
IBASIN 0324-0325 804-805 KERNAL CHRIN Routine
IBSOUT 0326-0327 806-807 KERNAL CHROUT Routine
ISTOP 0328-0329 808-809 KERNAL STOP Routine Vector
IGETIN 032A-032B 810-811 KERNAL GETIN Routine
ICLALL 032C-032D 812-813 KERNAL CLALL Routine Vector
USRCMD 032E-032F 814-815 User-Defined Vector
ILOAD 0330-0331 813-817 KERNAL LOAD Routine
ISAVE 0332-0333 818-819 KERNAL SAVE Routine Vector
0334-033B 820-827 Unused
TBUFFR 033C-03FB 828-1019 Tape I/O Buffer
03FC-03FF 1020-1023 Unused
VICSCN 0400-07FF 1024-2047 1024 Byte Screen Memory Area
0400-07E7 1024-2023 Video Matrix: 25 Lines X 40 Columns
07F8-07FF 2040-2047 Sprite Data Pointers
0800-9FFF 2048-40959 Normal BASIC Program Space
8000-9FFF 32768-40959 VSP Cartridge ROM - 8192 Bytes
A000-BFFF 40960-49151 BASIC ROM - 8192 Bytes (or 8K RAM)
C000-CFFF 49152-53247 RAM - 4096 Bytes
D000-DFFF 53248-57343 Input/Output Devices and
Color RAM or Character Generator ROM
or RAM - 4096 Bytes
E000-FFFF 57344-65535 KERNAL ROM - 8192 Bytes (or 8K RAM)
316 BASIC TO MACHINE LANGUAGE
~
COMMODORE 64 INPUT/OUTPUT ASSIGNMENTS
HEX DECIMAL BITS DESCRIPTION
-------------------------------------------------------------------------
0000 0 7-0 MOS 6510 Data Direction
Register (xx101111)
Bit= 1: Output, Bit=0:
Input, x=Don't Care
0001 1 MOS 6510 Micro-Processor
On-Chip I/O Port
0 /LORAM Signal (0=Switch BASIC ROM Out)
1 /HIRAM Signal (0=Switch Kernal ROM Out)
2 /CHAREN Signal (0=Switch Char. ROM In)
3 Cassette Data Output Line
4 Cassette Switch Sense: 1 = Switch Closed
5 Cassette Motor Control 0 = ON, 1 = OFF
6-7 Undefined
D000-D02E 53248-54271 MOS 6566 VIDEO INTERFACE CONTROLLER
(VIC)
D000 53248 Sprite 0 X Pos
D001 53249 Sprite 0 Y Pos
D002 53250 Sprite 1 X Pos
D003 53251 Sprite 1 Y Pos
D004 53252 Sprite 2 X Pos
D005 53253 Sprite 2 Y Pos
D006 53254 Sprite 3 X Pos
D007 53255 Sprite 3 Y Pos
D008 53256 Sprite 4 X Pos
D009 53257 Sprite 4 Y Pos
D00A 53258 Sprite 5 X Pos
D00B 53259 Sprite 5 Y Pos
D00C 53260 Sprite 6 X Pos
D00D 53261 Sprite 6 Y Pos
D00E 53262 Sprite 7 X Pos
D00F 53263 Sprite 7 Y Pos
BASIC TO MACHINE LANGUAGE 317
~
HEX DECIMAL BITS DESCRIPTION
-------------------------------------------------------------------------
D010 53264 Sprites 0-7 X Pos (msb of X coord.)
D011 53265 VIC Control Register
7 Raster Compare: (Bit 8) See 53266
6 Extended Color Text Mode 1 = Enable
5 Bit Map Mode. 1 = Enable
4 Blank Screen to Border Color: 0 = Blank
3 Select 24/25 Row Text Display: 1=25 Rows
2-0 Smooth Scroll to Y Dot-Position (0-7)
D012 53266 Read Raster/Write Raster Value for
Compare IRQ
D013 53267 Light-Pen Latch X Pos
D014 53268 Light-Pen Latch Y Pos
D015 53269 Sprite display Enable: 1 = Enable
D016 53270 VIC Control Register
7-6 Unused
5 ALWAYS SET THIS BIT TO 0 !
4 Multi-Color Mode: 1 = Enable (Text or
Bit-Map)
3 Select 38/40 Column Text Display:
1 = 40 Cols
2-0 Smooth Scroll to X Pos
D017 53271 Sprites 0-7 Expand 2x Vertical (Y)
D018 53272 VIC Memory Control Register
7-4 Video Matrix Base Address (inside VIC)
3-1 Character Dot-Data Base Address (inside
VIC)
0 Select upper/lower Character Set
D019 53273 VIC Interrupt Flag Register (Bit = 1:
IRQ Occurred)
7 Set on Any Enabled VIC IRQ Condition
3 Light-Pen Triggered IRQ Flag
2 Sprite to Sprite Collision IRQ Flag
1 Sprite to Background Collision IRQ Flag
0 Raster Compare IRQ Flag
318 BASIC TO MACHINE LANGUAGE
~
HEX DECIMAL BITS DESCRIPTION
-------------------------------------------------------------------------
D01A 53274 IRQ Mask Register: 1 = Interrupt Enabled
D01B 53275 Sprite to Background Display Priority:
1 = Sprite
D01C 53276 Sprites 0-7 Multi-Color Mode Select:
1 = M.C.M.
D01D 53277 Sprites 0-7 Expand 2x Horizontal (X)
D01E 53278 Sprite to Sprite Collision Detect
D01F 53279 Sprite to Background Collision Detect
D020 53280 Border Color
D021 53281 Background Color 0
D022 53282 Background Color 1
D023 53283 Background Color 2
D024 53284 Background Color 3
D025 53285 Sprite Multi-Color Register 0
D026 53286 Sprite Multi-Color Register 1
D027 53287 Sprite 0 Color
D028 53288 Sprite 1 Color
D029 53289 Sprite 2 Color
D02A 53290 Sprite 3 Color
D02B 53291 Sprite 4 Color
D02C 53292 Sprite 5 Color
D02D 53293 Sprite 6 Color
D02E 53294 Sprite 7 Color
D400-D7FF 54272-55295 MOS 6581 SOUND INTERFACE DEVICE (SID)
D400 54272 Voice 1: Frequency Control - Low-Byte
D401 54273 Voice 1: Frequency Control - High-Byte
D402 54274 Voice 1: Pulse Waveform Width - Low-Byte
D403 54275 7-4 Unused
3-0 Voice 1: Pulse Waveform Width - High-
Nybble
D404 54276 Voice 1: Control Register
7 Select Random Noise Waveform, 1 = On
6 Select Pulse Waveform, 1 = On
5 Select Sawtooth Waveform, 1 = On
4 Select Triangle Waveform, 1 = On
BASIC TO MACHINE LANGUAGE 319
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HEX DECIMAL BITS DESCRIPTION
-------------------------------------------------------------------------
3 Test Bit: 1 = Disable Oscillator 1
2 Ring Modulate Osc. 1 with Osc. 3 Output,
1 = On
1 Synchronize Osc.1 with Osc.3 Frequency,
1 = On
0 Gate Bit: 1 = Start Att/Dec/Sus,
0 = Start Release
D405 54277 Envelope Generator 1: Attack/Decay Cycle
Control
7-4 Select Attack Cycle Duration: 0-15
3-0 Select Decay Cycle Duration: 0-15
D406 54278 Envelope Generator 1: Sustain/Release
Cycle Control
7-4 Select Sustain Cycle Duration: 0-15
3-0 Select Release Cycle Duration: 0-15
D407 54279 Voice 2: Frequency Control - Low-Byte
D408 54280 Voice 2: Frequency Control - High-Byte
D409 54281 Voice 2: Pulse Waveform Width - Low-Byte
D40A 54282 7-4 Unused
3-0 Voice 2: Pulse Waveform Width - High-
Nybble
D40B 54283 Voice 2: Control Register
7 Select Random Noise Waveform, 1 = On
6 Select Pulse Waveform, 1 = On
5 Select Sawtooth Waveform, 1 = On
4 Select Triangle Waveform, 1 = On
3 Test Bit: 1 = Disable Oscillator 1
2 Ring Modulate Osc. 2 with Osc. 1 Output,
1 = On
1 Synchronize Osc.2 with Osc. 1 Frequency,
1 = On
0 Gate Bit: 1 = Start Att/Dec/Sus,
0 = Start Release
320 BASIC TO MACHINE LANGUAGE
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HEX DECIMAL BITS DESCRIPTION
-------------------------------------------------------------------------
D40C 54284 Envelope Generator 2: Attack / Decay
Cycle Control
7-4 Select Attack Cycle Duration: 0-15
3-0 Select Decay Cycle Duration: 0-15
D40D 54285 Envelope Generator 2: Sustain / Release
Cycle Control
7-4 Select Sustain Cycle Duration: 0-15
3-0 Select Release Cycle Duration: 0-15
D40E 54286 Voice 3: Frequency Control - Low-Byte
D40F 54287 Voice 3: Frequency Control - High-Byte
D410 54288 Voice 3: Pulse Waveform Width - Low-Byte
D411 54289 7-4 Unused
3-0 Voice 3: Pulse Waveform Width - High-
Nybble
D412 54290 Voice 3: Control Register
7 Select Random Noise Waveform, 1 = On
6 Select Pulse Waveform, 1 = On
5 Select Sawtooth Waveform, 1 = On
4 Select Triangle Waveform, 1 = On
3 Test Bit: 1 = Disable Oscillator 1
2 Ring Modulate Osc. 3 with Osc. 2 Output,
1 = On
1 Synchronize Osc. 3 with Osc.2 Frequency,
1 = On
0 Gate Bit: 1 = Start Att/Dec/Sus,
0 = Start Release
D413 54291 Envelope Generator 3: Attack/Decay Cycle
Control
7-4 Select Attack Cycle Duration: 0-15
3-0 Select Decay Cycle Duration: 0-15
D414 54285 Envelope Generator 3: Sustain / Release
Cycle Control
7-4 Select Sustain Cycle Duration: 0-15
3-0 Select Release Cycle Duration: 0-15
BASIC TO MACHINE LANGUAGE 321
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HEX DECIMAL BITS DESCRIPTION
-------------------------------------------------------------------------
D415 54293 Filter Cutoff Frequency: Low-Nybble
(Bits 2-0)
D416 54294 Filter Cutoff Frequency: High-Byte
D417 54295 Filter Resonance Control / Voice Input
Control
7-4 Select Filter Resonance: 0-15
3 Filter External Input: 1 = Yes, 0 = No
2 Filter Voice 3 Output: 1 = Yes, 0 = No
Filter Voice 2 Output: 1 = Yes, 0 = No
0 Filter Voice 1 Output: 1 = Yes, 0 = No
D418 54296 Select Filter Mode and Volume
7 Cut-Off Voice 3 Output: 1 = Off, 0 = On
6 Select Filter High-Pass Mode: 1 = On
5 Select Filter Band-Pass Mode: 1 = On
4 Select Filter Low-Pass Mode: 1 = On
3-0 Select Output Volume: 0-15
D419 54297 Analog/Digital Converter: Game Paddle 1
(0-255)
D41A 54298 Analog/Digital Converter: Game Paddle 2
(0-255)
D41B 54299 Oscillator 3 Random Number Generator
D41C 54230 Envelope Generator 3 Output
D500-D7FF 54528-55295 SID IMAGES
D800-DBFF 55296-56319 Color RAM (Nybbles)
DC00-DCFF 56320-56575 MOS 6526 Complex Interface Adapter
(CIA) #1
DC00 56320 Data Port A (Keyboard, Joystick,
Paddles, Light-Pen)
7-0 Write Keyboard Column Values for
Keyboard Scan
7-6 Read Paddles on Port A / B (01 = Port A,
10 = Port B)
4 Joystick A Fire Button: 1 = Fire
3-2 Paddle Fire Buttons
3-0 Joystick A Direction (0-15)
322 BASIC TO MACHINE LANGUAGE
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HEX DECIMAL BITS DESCRIPTION
-------------------------------------------------------------------------
DC01 56321 Data Port B (Keyboard, Joystick,
Paddles): Game Port 1
7-0 Read Keyboard Row Values for Keyboard
Scan
7 Timer B Toggle/Pulse Output
6 Timer A: Toggle/Pulse Output
4 Joystick 1 Fire Button: 1 = Fire
3-2 Paddle Fire Buttons
3-0 Joystick 1 Direction
DC02 56322 Data Direction Register - Port A (56320)
DC03 56323 Data Direction Register - Port B (56321)
DC04 56324 Timer A: Low-Byte
DC05 56325 Timer A: High-Byte
DC06 56326 Timer B: Low-Byte
DC07 56327 Timer B: High-Byte
DC08 56328 Time-of-Day Clock: 1/10 Seconds
DC09 56329 Time-of-Day Clock: Seconds
DC0A 56330 Time-of-Day Clock: Minutes
DC0B 56331 Time-of-Day Clock: Hours + AM/PM Flag
(Bit 7)
DC0C 56332 Synchronous Serial I/O Data Buffer
DC0D 56333 CIA Interrupt Control Register
(Read IRQs/Write Mask)
7 IRQ Flag (1 = IRQ Occurred) / Set-
Clear Flag
4 FLAG1 IRQ (Cassette Read / Serial Bus
SRQ Input)
3 Serial Port Interrupt
2 Time-of-Day Clock Alarm Interrupt
1 Timer B Interrupt
0 Timer A Interrupt
BASIC TO MACHINE LANGUAGE 323
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HEX DECIMAL BITS DESCRIPTION
-------------------------------------------------------------------------
DC0E 56334 CIA Control Register A
7 Time-of-Day Clock Frequency: 1 = 50 Hz,
0 = 60 Hz
6 Serial Port I/O Mode Output, 0 = Input
5 Timer A Counts: 1 = CNT Signals,
0 = System 02 Clock
4 Force Load Timer A: 1 = Yes
3 Timer A Run Mode: 1 = One-Shot,
0 = Continuous
2 Timer A Output Mode to PB6: 1 = Toggle,
0 = Pulse
1 Timer A Output on PB6: 1 = Yes, 0 = No
0 Start/Stop Timer A: 1 = Start, 0 = Stop
DC0F 56335 CIA Control Register B
7 Set Alarm/TOD-Clock: 1 = Alarm,
0 = Clock
6-5 Timer B Mode Select:
00 = Count System 02 Clock Pulses
01 = Count Positive CNT Transitions
10 = Count Timer A Underflow Pulses
11 = Count Timer A Underflows While
CNT Positive
4-0 Same as CIA Control Reg. A - for Timer B
DD00-DDFF 56576-56831 MOS 6526 Complex Interface Adapter
(CIA) #2
DD00 56576 Data Port A (Serial Bus, RS-232, VIC
Memory Control)
7 Serial Bus Data Input
6 Serial Bus Clock Pulse Input
5 Serial Bus Data Output
4 Serial Bus Clock Pulse Output
3 Serial Bus ATN Signal Output
2 RS-232 Data Output (User Port)
1-0 VIC Chip System Memory Bank Select
(Default = 11)
324 BASIC TO MACHINE LANGUAGE
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HEX DECIMAL BITS DESCRIPTION
-------------------------------------------------------------------------
DD01 56577 Data Port B (User Port, RS-232)
7 User / RS-232 Data Set Ready
6 User / RS-232 Clear to Send
5 User
4 User / RS-232 Carrier Detect
3 User / RS-232 Ring Indicator
2 User / RS-232 Data Terminal Ready
1 User / RS-232 Request to Send
0 User / RS-232 Received Data
DD02 56578 Data Direction Register - Port A
DD03 56579 Data Direction Register - Port B
DD04 56580 Timer A: Low-Byte
DD05 56581 Timer A: High-Byte
DD06 56582 Timer B: Low-Byte
DD07 56583 Timer B: High-Byte
DD08 56584 Time-of-Day Clock: 1/10 Seconds
DD09 56585 Time-of-Day Clock: Seconds
DD0A 56586 Time-of-Day Clock: Minutes
DD0B 56587 Time-of-Day Clock: Hours + AM/PM Flag
(Bit 7)
DD0C 56588 Synchronous Serial I/O Data Buffer
DD0D 56589 CIA Interrupt Control Register (Read
NMls/Write Mask)
7 NMI Flag (1 = NMI Occurred) / Set-
Clear Flag
4 FLAG1 NMI (User/RS-232 Received Data
Input)
3 Serial Port Interrupt
1 Timer B Interrupt
0 Timer A Interrupt
DD0E 56590 CIA Control Register A
7 Time-of-Day Clock Frequency: 1 = 50 Hz,
0 = 60 Hz
6 Serial Port I/O Mode Output, 0 = Input
5 Timer A Counts: 1 = CNT Signals,
0 = System 02 Clock
4 Force Load Timer A: 1 = Yes
BASIC TO MACHINE LANGUAGE 325
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HEX DECIMAL BITS DESCRIPTION
-------------------------------------------------------------------------
3 Timer A Run Mode: 1 = One-Shot,
0 = Continuous
2 Timer A Output Mode to PB6: 1 = Toggle,
0 = Pulse
1 Timer A Output on PB6: 1 = Yes, 0 = No
0 Start/Stop Timer A: 1 = Start, 0 = Stop
DD0F 56591 CIA Control Register B
7 Set Alarm/TOD-Clock: 1=Alarm, 0=Clock
6-5 Timer B Mode Select:
00 = Count System 02 Clock Pulses
01 = Count Positive CNT Transitions
10 = Count Timer A Underflow Pulses
11 = Count Timer A Underflows While
CNT Positive
4-0 Same as CIA Control Reg. A - for Timer B
DE00-DEFF 56832-57087 Reserved for Future I/O Expansion
DF00-DFFF 57088-57343 Reserved for Future I/O Expansion
326 BASIC TO MACHINE LANGUAGE
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CHAPTER 6
INPUT/OUTPUT
GUIDE
o Introduction
o Output to the TV
o Output to Other Devices
o The Game Ports
o RS-232 Interface Description
o The User Port
o The Serial Bus
o The Expansion Port
o Z-80 Microprocessor Cartridge
335
~
INTRODUCTION
Computers have three basic abilities: they can calculate, make deci-
sions, and communicate. Calculation is probably the easiest to program.
Most of the rules of mathematics are familiar to us. Decision making is
not too difficult, since the rules of logic are relatively few, even if
you don't know them too well yet.
Communication is the most complex, because it involves the least
exacting set of rules. This is not an oversight in the design of
computers. The rules allow enough flexibility to communicate virtually
anything, and in many possible ways. The only real rule is this: whatever
sends information must present the information so that it can be
understood by the receiver.
OUTPUT TO THE TV
The simplest form of output in BASIC is the PRINT statement. PRINT uses
the TV screen as the output device, and your eyes are the input device
because they use the information on the screen.
When PRINTing on the screen, your main objective is to format the
information on the screen so it's easy to read. You should try to think
like a graphic artist, using colors, placement of letters, capital and
lower case letters, as well as graphics to best communicate the
information. Remember, no matter how smart your program, you want to be
able to understand what the results mean to you.
The PRINT statement uses certain character codes as "commands" to the
cursor. The <CRSR> key doesn't actually display anything, it just makes
the cursor change position. Other commands change colors, clear the
screen, and insert or delete spaces. The <RETURN> key has a character
code number (CHR$) of 13. A complete table of these codes is contained in
Appendix C.
There are two functions in the BASIC language that work with the PRINT
statement. TAB positions the,cursor on the given position from the left
edge of the screen, SPC moves the cursor right a given number of spaces
from the current position.
Punctuation marks in the PRINT statement serve to separate and format
information. The semicolon (;) separates 2 items without any spaces in
between. If it is the last thing on a line, the cursor remains after the
last thing PRINTed instead of going down to the next line. It suppresses
336 INPUT/OUTPUT GUIDE
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(replaces) the RETURN character that is normally PRINTed at the end of
the line.
The comma (,) separates items into columns. The Commodore 64 has 4
columns of 10 characters each on the screen. When the computer PRINTs a
comma, it moves the cursor right to the start of the next column. If it
is past the last column of the line, it moves the cursor down to the next
line. Like the semicolon, if it is the last item on a line the RETURN is
suppressed.
The quote marks ("") separate literal text from variables. The first
quote mark on the line starts the literal area, and the next quote mark
ends it. By the way, you don't have to have a final quote mark at the
end of the line.
The RETURN code (CHR$ code of 13) makes the cursor go to the next
logical line on the screen. This is not always the very next line. When
you type past the end of a line, that line is linked to the next line.
The computer knows that both lines are really one long line. The links
are held in the line link table (see the memory map for how this is set
up).
A logical line can be 1 or 2 screen lines long, depending on what was
typed or PRINTed. The logical line the cursor is on determines where the
<RETURN> key sends it. The logical line at the top of the screen
determines if the screen scrolls 1 or 2 lines at a time. There are other
ways to use the TV as an output device. The chapter on graphics describes
the commands to create objects that move across the screen. The VIC chip
section tells how the screen and border colors and sizes are changed. And
the sound chapter tells how the TV speaker creates music and special
effects.
OUTPUT TO OTHER DEVICES
It is often necessary to send output to devices other than the screen,
like a cassette deck, printer, disk drive, or modem. The OPEN statement
in BASIC creates a "channel" to talk to one of these devices. Once the
channel is OPEN, the PRINT# statement will send characters to that
device.
EXAMPLE of OPEN and PRINT# Statements:
100 OPEN 4,4: PRINT# 4, "WRITING ON PRINTER"
110 OPEN 3,8,3,"0:DISK-FILE,S,W":PRINT#3,"SEND TO DISK"
120 OPEN 1,1,1,"TAPE-FILE": PRINT#1,"WRITE ON TAPE"
130 OPEN 2,2,0,CHR$(10):PRINT#2,"SEND TO MODEM"
INPUT/OUTPUT GUIDE 337
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The OPEN statement is somewhat different for each device. The pa-
rameters in the OPEN statement are shown in the table below for each
device.
TABLE of OPEN Statement Parameters:
FORMAT: OPEN file#, device#, number, string
+--------+---------+---------------------+------------------------------+
| DEVICE | DEVICE# | NUMBER | STRING |
+--------+---------+---------------------+------------------------------+
|CASSETTE| 1 | 0 = Input | File Name |
| | | 1 = Output | |
| | | 2 = Output with EOT | |
| MODEM | 2 | 0 | Control Registers |
| SCREEN | 3 | 0,1 | |
| PRINTER| 4 or 5 | 0 = Upper/Graphics | Text Is PRINTed |
| | | 7 = Upper/Lower Case| |
| DISK | 8 to 11 | 2-14 = Data Channel | Drive #, File Name |
| | | | File Type, Read/Write |
| | | 15 = Command | Command |
| | | Channel | |
+--------+---------+---------------------+------------------------------+
OUTPUT TO PRINTER
The printer is an output device similar to the screen. Your main con-
cern when sending output to the printer is to create a format that is
easy on the eyes. Your tools here include reversed, double-width, capital
and lower case letters, as well as dot-programmable graphics.
The SPC function works for the printer in the same way it works for the
screen. However, the TAB function does not work correctly on the printer,
because it calculates the current position on the line based on the
cursor's position on the screen, not on the paper.
The OPEN statement for the printer creates the channel for communi-
cation. It also specifies which character set will be used, either upper
case with graphics or upper and lower case.
EXAMPLES of OPEN Statement for Printer:
OPEN 1,4: REM UPPER CASE/GRAPHICS
OPEN 1,4,7: REM UPPER AND LOWER CASE
338 INPUT/OUTPUT GUIDE
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When working with one character set, individual lines can be PRINTed
in the opposite character set. When in upper case with graphics, the
cursor down character (CHR$(17)) switches the characters to the upper
and lower case set. When in upper and lower case, the cursor up char-
acter (CHR$(145)) allows upper case and graphics characters to be
PRINTed.
Other special functions in the printer are controlled through character
codes. All these codes are simply PRINTed just like any other character.
TABLE of Printer Control Character Codes:
+----------+------------------------------------------------------------+
| CHR$ CODE| PURPOSE |
+----------+------------------------------------------------------------+
| 10 | Line feed |
| 13 | RETURN (automatic line feed on CBM printers) |
| 14 | Begin double-width character mode |
| 15 | End double-width character mode |
| 18 | Begin reverse character mode |
| 146 | End reverse character mode |
| 17 | Switch to upper/lower case character set |
| 145 | Switch to upper case/graphics character set |
| 16 | Tab to position in next 2 characters |
| 27 | Move to specified dot position |
| 8 | Begin dot-programmable graphic mode |
| 26 | Repeat graphics data |
+----------+------------------------------------------------------------+
See your Commodore printer's manual for details on using the command
codes.
OUTPUT TO MODEM
The modem is a simple device that can translate character codes into
audio pulses and vice-versa, so that computers can communicate over
telephone lines. The OPEN statement for the modem sets up the parameters
to match the speed and format of the other computer you are communicating
with. Two characters can be sent in the string at the end
of the OPEN statement.
The bit positions of the first character code determine the baud rate,
number of data bits, and number of stop bits. The second code is op-
tional, and its bits specify the parity and duplex of the transmission.
See the RS-232 section or your VICMODEM manual for specific details on
this device.
INPUT/OUTPUT GUIDE 339
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EXAMPLE of OPEN Statement for Modem:
OPEN 1,2,0,CHR$(6): REM 300 BAUD
100 OPEN 2,2,0,CHR$(163) CHR$(112): REM 110 BAUD, ETC.
Most computers use the American Standard Code for Information In-
terchange, known as ASCII (pronounced ASK-KEY). This standard set of
character codes is somewhat different from the codes used in the Com-
modore 64. When communicating with other computers, the Commodore
character codes must be translated into their ASCII counterparts. A table
of standard ASCII codes is included in this book in Appendix C.
Output to the modem is a fairly uncomplicated task, aside from the need
for character translation. However, you must know the receiving device
fairly well, especially when writing programs where your computer "talks"
to another computer without human intervention. An example of this would
be a terminal program that automatically types in your account number and
secret password. To do this successfully, you must carefully count the
number of characters and RETURN characters. Otherwise, the computer
receiving the characters won't know what to do with them.
WORKING WITH CASSETTE TAPE
Cassette tapes have an almost unlimited capacity for data. The longer
the tape, the more information it can store. However, tapes are limited
in time. The more data on the tape, the longer the time it takes to find
the information.
The programmer must try to minimize the time factor when working with
tape storage. One common practice is to read the entire cassette data
file into RAM, then process it, and then re-write all the data on the
tape. This allows you to sort, edit, and examine your data. However, this
limits the size of your files to the amount of available RAM.
If your data file is larger than the available RAM, it is probably time
to switch to using the floppy disk. The disk can read data at any
position on the disk, without needing to read through all the other data.
You can write data over old data without disturbing the rest of the file.
That's why the disk is used for all business applications like ledgers
and mailing lists.
The PRINT# statement formats data just like the PRINT statement does.
All punctuation works the same. But remember, you're not working with the
screen now. The formatting must be done with the INPUT# statement
constantly in mind.
340 INPUT/OUTPUT GUIDE
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Consider the statement PRINT# 1, A$, B$, C$. When used with the screen,
the commas between the variables provide enough blank space between items
to format them into columns ten characters wide. On cassette, anywhere
from 1 to 10 spaces will be added, depending on th length of the strings.
This wastes space on your tape.
Even worse is what happens when the INPUT# statement tries to read
these strings. The statement INPUT# 1, A$, B$, C$ will discover no data
for B$ and C$. A$ will contain all three variables, plus the spaces be-
tween them. What happens? Here's a look at the tape file:
A$="DOG" B$="CAT" C$="TREE"
PRINT# 1, A$, B$, C$
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
D O G C A T T R E E RETURN
The INPUT# statement works like the regular INPUT statement. When
typing data into the INPUT statement, the data items are separated,
either by hitting the <RETURN> key or using commas to separate them. The
PRINT# statement puts a RETURN at the end of a line just like the PRINT
statement. A$ fills up with all three values because there's no separator
on the tape between them, only after all three.
A proper separator would be a comma (,) or a RETURN on the tape. The
RETURN code is automatically put at the end of a PRINT or PRINT#
statement. One way to put the RETURN code between each item is to us only
one item per PRINT# statement. A better way is to set a variable to the
RETURN CHR$ code, which is CHR$(13), or use a comma. The statement for
this is R$=",":PRINT#1, A$ R$ B$ R$ C$. Don't use commas or any other
punctuation between the variable names, since the Commodore 64 can tell
them apart and they'll only use up space in your program.
A proper tape file looks like this:
1 2 3 4 5 6 7 8 9 10 11 12 13
D O G , C A T , T R E E RETURN
The GET# statement will pick data from the tape one character at a
time. It will receive each character, including the RETURN code and other
punctuation. The CHR$(0) code is received as an empty string, not as a
one character string with a code of 0. If you try to use the ASC function
on an empty string, you get the error message ILLEGAL QUANTITY ERROR.
INPUT/OUTPUT GUIDE 341
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The line GET# 1, A$: A= ASC(A$) is commonly used in programs to examine
tape data. To avoid error messages, the line should be modified to
GET#1, A$: A=ASC(A$+CHR$(0)). The CHR$(0) at the end acts as insurance
against empty strings, but doesn't affect the ASC function when there are
other characters in A$.
DATA STORAGE ON FLOPPY DISKETTES
Diskettes allow 3 different forms of data storage. Sequential files are
similar to those on tape, but several can can be used at the same time.
Relative files let you organize the data into records, and then read and
replace individual records within the file. Random files let you work
with data anywhere on the disk. They are organized into 256 byte sections
called blocks.
The PRINT# statement's limitations are discussed in the section on
cassette tape. The same limitations to format apply on the disk. RETURNs
or commas are needed to separate your data. The CHR$(0) is still read by
the GET# statement as an empty string.
Relative and random files both make use of separate data and command
"channels." Data written to the disk goes through the data channel, where
it is stored in a temporary buffer in the disk's RAM. When the record or
block is complete, a command is sent through the command channel that
tells the drive where to put the data, and the entire buffer is written.
Applications that require large amounts of data to be processed are
best stored in relative disk files. These will use the least amount of
time and provide the best flexibility for the programmer. Your disk drive
manual gives a complete programming guide to use of disk files.
342 INPUT/OUTPUT GUIDE
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THE GAME PORTS
The Commodore 64 has two 9-pin Game Ports which allow the use of
joysticks, paddies, or a light pen. Each port will accept either one joy-
stick or one paddle pair. A light pen can be plugged into Port A (only)
for special graphic control, etc. This section gives you examples of how
to use the joysticks and paddies from both BASIC and machine language.
The digital joystick is connected to CIA #1 (MOS 6526 Complex Interface
Adapter). This input/output device also handles the paddle fire buttons
and keyboard scanning. The 6526 CIA chip has 16 registers which are in
memory locations 56320 through 56335 inclusive ($DC00 to $DC0F). Port A
data appears at location 56320 (DC00) and Port B data is found at
location 56321 ($DC01).
A digital joystick has five distinct switches, four of the switches are
used for direction and one of the switches is used for the fire button.
The joystick switches are arranged as shown:
(Top)
FIRE
(Switch 4)
UP
(Switch 0)
|
|
|
LEFT | RIGHT
-------+-------
(Switch 2) | (Switch 3)
|
|
|
DOWN
(Switch 1)
These switches correspond to the lower 5 bits of the data in location
56320 or 56321. Normally the bit is set to a one if a direction is NOT
chosen or the fire button is NOT pressed. When the fire button is
INPUT/OUTPUT GUIDE 343
~
pressed, the bit (bit 4 in this case) changes to a 0. To read the
joystick from BASIC, the following subroutine should be used:
start tok64 page344.prg
10 fork=0to10:rem set up direction string
20 readdr$(k):next
30 data"","n","s","","w","nw"
40 data"sw","","e","ne","se"
50 print"going...";
60 gosub100:rem read the joystick
65 ifdr$(jv)=""then80:rem check if a direction was chosen
70 printdr$(jv);" ";:rem output which direction
80 iffr=16then60:rem check if fire button was pushed
90 print"-----f-----i-----r-----e-----!!!":goto60
100 jv=peek(56320):rem get joystick value
110 fr=jvand16:rem form fire button status
120 jv=15-(jvand15):rem form direction value
130 return
stop tok64
+-----------------------------------------------------------------------+
| NOTE: For the second joystick, set JV = PEEK (56321). |
+-----------------------------------------------------------------------+
The values for JV correspond to these directions:
+-------------+---------------+
| JV EQUAL TO | DIRECTION |
+-------------+---------------+
| 0 | NONE |
| 1 | UP |
| 2 | DOWN |
| 3 | - |
| 4 | LEFT |
| 5 | UP & LEFT |
| 6 | DOWN & LEFT |
| 7 | - |
| 8 | RIGHT |
| 9 | UP & RIGHT |
| 10 | DOWN & RIGHT |
+-------------+---------------+
344 INPUT/OUTPUT GUIDE
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A small machine code routine which accomplishes the same task is as
follows:
; joystick - button read routine
;
; author - bill hindorff
;
dx = $c110
dy = $c111
* = $c200
djrr lda $dc00 ; get input from port a only
djrrb ldy #0 ; this routine reads and decodes the
ldx #0 ; joystick/firebutton input data in
lsr a ; the accumulator. this least significant
bcs djr0 ; 5 bits contain the switch closure
dey ; information. if a switch is closed then it
djr0 lsr a ; produces a zero bit. if a switch is open then
bcs djr1 ; it produces a one bit. The joystick dir-
iny ; ections are right, left, forward, backward
djr1 lsr a ; bit3=right, bit2=left, bit1=backward,
bcs djr2 ; bit0=forward and bit4=fire button.
dex ; at rts time dx and dy contain 2's compliment
djr2 lsr a ; direction numbers i.e. $ff=-1, $00=0, $01=1.
bcs djr3 ; dx=1 (move right), dx=-1 (move left),
inx ; dx=0 (no x change). dy=-1 (move up screen),
djr3 lsr a ; dy=0 (move down screen), dy=0 (no y change).
stx dx ; the forward joystick position corresponds
sty dy ; to move up the screen and the backward
rts ; position to move down screen.
;
; at rts time the carry flag contains the fire
; button state. if c=1 then button not pressed.
; if c=0 then pressed.
.end
INPUT/OUTPUT GUIDE 345
~
PADDLES
A paddle is connected to both CIA #1 and the SID chip (MOS 6581 Sound
Interface Device) through a game port. The paddle value is read via the
SID registers 54297 ($D419) and 54298 ($D41A). PADDLES ARE NOT RELIABLE
WHEN READ FROM BASIC ALONE!!!! The best way to use paddles, from BASIC or
machine code, is to use the following machine language routine... (SYS to
it from BASIC then PEEK the memory locations used by the subroutine).
; four paddle read routine (can also be used for two)
;
; author - bill hindorff
;
porta=$dc00
ciddra=$dc02
sid=$d400
*=$c100
buffer *=*+1
pdlx *=*+2
pdly *=*+2
btna *=*+1
btnb *=*+1
* = $c000
pdlrd ldx #1 ; for four paddles or two analog joysticks
pdlrd0 ; entry point for one pair (condition x 1st)
sei
lda ciddra ; get current value of ddr
sta buffer ; save it away
lda #$c0
sta ciddra ; set port a for input
lda #$80
pdlrd1
sta porta ; address a pair of paddles
ldy #$80 ; wait a while
pdlrd2
nop
dey
bpl pdlrd2
lda sid+25 ; get x value
sta pdlx,x
lda sid+26
sta pdly,x ; get y value
lda porta ; time to read paddle fire buttons
ora #80 ; make it the same as other pair
sta btna ; bit 2 is pdl x, bit 3 is pdl y
lda #$40
dex ; all pairs done?
bpl pdlrd1 ; no
lda buffer
sta ciddra ; restore previous value of ddr
lda porta+1 ; for 2nd pair -
sta btnb ; bit 2 is pdl x, bit 3 is pdl y
cli
rts
.end
The paddles can be read by using the following BASIC program:
start tok64 page347.prg
10 c=12*4096:rem set paddle routine start
11 rem poke in the paddle reading routine
15 fori=0to63:reada:pokec+i,a:next
20 sysc:rem call the paddle routine
30 p1=peek(c+257):rem set paddle one value
40 p2=peek(c+258):rem set paddle two value
50 p3=peek(c+259):rem set paddle three value
60 p4=peek(c+260):rem set paddle four value
61 rem read fire button status
62 s1=peek(c+261):s2=peek(c+262)
70 printp1,p2,p3,p4:rem print paddle values
72 rem print fire button status
75 print:print"fire a ";s1,"fire b ";s2
80 forw=1to50:next:rem wait a while
90 print"{clear}":print:goto20:rem clear screen and do again
95 rem data for machine code routine
100 data162,1,120,173,2,220,141,0,193,169,192,141,2,220,169
110 data128,141,0,220,160,128,234,136,16,252,173,25,212,157
120 data1,193,173,26,212,157,3,193,173,0,220,9,128,141,5,193
130 data169,64,202,16,222,173,0,193,141,2,220,173,1,220,141
140 data6,193,88,96
stop tok64
INPUT/OUTPUT GUIDE 347
~
LIGHT PEN
The light pen input latches the current screen position into a pair of
registers (LPX, LPY) on a low-going edge. The X position register 19
($13) will contain the 8 MSB of the X position at the time of transition.
Since the X position is defined by a 512-state counter (9 bits),
resolution to 2 horizontal dots is provided. Similarly, the Y position is
latched in its register 20 ($14), but here 8 bits provide single raster
resolution within the visible display. The light pen latch may be
triggered only once per frame, and subsequent triggers within the same
frame will have no effect. Therefore, you must take several samples
before turning the pen to the screen (3 or more samples average),
depending upon the characteristics of your light pen.
RS-232 INTERFACE DESCRIPTION
GENERAL OUTLINE
The Commodore 64 has a built-in RS-232 interface for connection to any
RS-232 modem, printer, or other device. To connect a device to the
Commodore 64, all you need is a cable and a little bit of programming.
RS-232 on the Commodore 64 is set-up in the standard RS-232 format, but
the voltages are TTL levels (0 to 5V) rather than the normal RS-232 -12
to 12 volt range. The cable between the Commodore 64 and the RS-232
device should take care of the necessary voltage conversions. The
Commodore RS-232 interface cartridge handles this properly.
The RS-232 interface software can be accessed from BASIC or from the
KERNAL for machine language programming.
RS-232 on the BASIC level uses the normal BASIC commands: OPEN, CLOSE,
CMD, INPUT#, GET#, PRINT#, and the reserved variable ST. INPUT# and GET#
fetch data from the receiving buffer, while PRINT# and CMD place data
into the transmitting buffer. The use of these commands (and examples)
will be described in more detail later in this chapter.
The RS-232 KERNAL byte and bit level handlers run under the control of
the 6526 CIA #2 device timers and interrupts. The 6526 chip generates
348 INPUT/OUTPUT GUIDE
~
NMI (Non-Maskable Interrupt) requests for RS-232 processing. This allows
background RS-232 processing to take place during BASIC and machine
language programs. There are built-in hold-offs in the KERNAL, cassette,
and serial bus routines to prevent the disruption of data storage or
transmission by the NMIs that are generated by the RS-232 routines.
During cassette or serial bus activities, data can NOT be received from
RS-232 devices. But because these hold-offs are only local (assuming
you're careful about your programming) no interference should result.
There are two buffers in the Commodore 64 RS-232 interface to help
prevent the loss of data when transmitting or receiving RS-232 informa-
tion.
The Commodore 64 RS-232 KERNAL buffers consist of two first-in/first-
out (FIFO) buffers, each 256 bytes long, at the top of memory. The
OPENing of an RS-232 channel automatically allocates 512 bytes of memory
for these buffers. If there is not enough free space beyond the end of
your BASIC program no error message will be printed, and the end of your
program will be destroyed. SO BE CAREFUL!
These buffers are automatically removed by using the CLOSE command.
OPENING AN RS-232 CHANNEL
Only one RS-232 channel should be open at any time; a second OPEN
statement will cause the buffer pointers to be reset. Any characters in
either the transmit buffer or the receive buffer will be lost.
Up to 4 characters can be sent in the filename field. The first two are
the control and command register characters; the other two are reserved
for future system options. Baud rate, parity, and other options can be
selected through this feature.
No error-checking is done on the control word to detect a non-
implemented baud rate. Any illegal control word will cause the system
output to operate at a very slow rate (below 50 baud).
BASIC SYNTAX:
OPEN lfn,2,0,"<control register><command register><opt baud low><opt
baud high>"
lfn-The logical file number (lfn) then can be any number from 1 through
255. But be aware of the fact that if you choose a logical file number
that is greater than 127, then a line feed will follow all carriage
returns.
INPUT/OUTPUT GUIDE 349
~
+-+-+-+ +-+ +-+-+-+-+
|7|6|5| |4| |3|2|1|0|
+-+-+-+ +-+ +-+-+-+-+ BAUD RATE
| | | | +-+-+-+-+----------------+
STOP BITS ----+ | | | |0|0|0|0| USER RATE [NI]|
| | | +-+-+-+-+----------------+
0 - 1 STOP BIT | | | |0|0|0|1| 50 BAUD |
1 - 2 STOP BITS | | | +-+-+-+-+----------------+
| | | |0|0|1|0| 75 |
| | | +-+-+-+-+----------------+
| | | |0|0|1|1| 110 |
| | | +-+-+-+-+----------------+
WORD LENGTH -----+-+ | |0|1|0|0| 134.5 |
| +-+-+-+-+----------------+
+---+-----------+ | |0|1|0|1| 150 |
|BIT| | | +-+-+-+-+----------------+
+-+-+ DATA | | |0|1|1|0| 300 |
|6|5|WORD LENGTH| | +-+-+-+-+----------------+
+-+-+-----------+ | |0|1|1|1| 600 |
|0|0| 8 BITS | | +-+-+-+-+----------------+
+-+-+-----------+ | |1|0|0|0| 1200 |
|0|1| 7 BITS | | +-+-+-+-+----------------+
+-+-+-----------+ | |1|0|0|1| (1800) 2400|
|1|0| 6 BITS | | +-+-+-+-+----------------+
+-+-+-----------+ | |1|0|1|0| 2400 |
|1|1| 5 BITS | | +-+-+-+-+----------------+
+-+-+-----------+ | |1|0|1|1| 3600 [NI]|
| +-+-+-+-+----------------+
| |1|1|0|0| 4800 [NI]|
UNUSED -------------+ +-+-+-+-+----------------+
|1|1|0|1| 7200 [NI]|
+-+-+-+-+----------------+
Figure 6-1. |1|1|1|0| 9600 [NI]|
Control Register Map. +-+-+-+-+----------------+
|1|1|1|1| 19200 [NI]|
+-+-+-+-+----------------+
<control register>- Is a single byte character (see Figure 6-1, Control
Register Map) required to specify the baud rates. If the lower 4 bits of
the baud rate is equal to zero (0), the <opt baud low><opt baud high>
characters give you a rate based on the following:
<opt baud low>=<system frequency/rate/2-100-<opt baud high>*256
<opt baud high>=INT((system frequency/rate/2-100)/256
350 INPUT/OUTPUT GUIDE
~
+-+-+-+-+-+-+-+-+
|7|6|5|4|3|2|1|0|
+-+-+-+-+-+-+-+-+
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
PARITY OPTIONS ----+-+-+ | | | | +----- HANDSHAKE
+---+---+---+---------------------+| | | |
|BIT|BIT|BIT| OPERATIONS || | | | 0 - 3-LINE
| 7 | 6 | 5 | || | | | 1 - X-LINE
+---+---+---+---------------------+| | | |
| - | - | 0 |PARITY DISABLED, NONE|| | | |
| | | |GENERATED/RECEIVED || | | |
+---+---+---+---------------------+| | | +------- UNUSED
| 0 | 0 | 1 |ODD PARITY || | +--------- UNUSED
| | | |RECEIVER/TRANSMITTER || +----------- UNUSED
+---+---+---+---------------------+|
| 0 | 1 | 1 |EVEN PARITY ||
| | | |RECEIVER/TRANSMITTER |+------------- DUPLEX
+---+---+---+---------------------+
| 1 | 0 | 1 |MARK TRANSMITTED | 0 - FULL DUPLEX
| | | |PARITY CHECK DISABLED| 1 - HALF DUPLEX
+---+---+---+---------------------+
| 1 | 1 | 1 |SPACE TRANSMITTED |
| | | |PARITY CHECK DISABLED|
+---+---+---+---------------------+
Figure 6-2. Command Register Map.
The formulas above are based on the fact that:
system frequency = 1.02273E6 NTSC (North American TV standard)
= 0.98525E6 PAL (U.K. and most European TV standard)
<command register>- Is a single byte character (see Figure 6-2, Command
Register Map) that defines other terminal parameters. This character is
NOT required.
INPUT/OUTPUT GUIDE 351
~
KERNAL ENTRY:
OPEN ($FFC0) (See KERNAL specifications for more information on entry
conditions and instructions.)
+-----------------------------------------------------------------------+
| IMPORTANT NOTE: In a BASIC program, the RS-232 OPEN command should be |
| performed before creating any variables or arrays because an automatic|
| CLR is performed when an RS-232 channel is OPENed (This is due to the |
| allocation of 512 bytes at the top of memory.) Also remember that your|
| program will be destroyed if 512 bytes of space are not available at |
| the time of the OPEN statement. |
+-----------------------------------------------------------------------+
GETTING DATA FROM AN RS-232 CHANNEL
When getting data from an RS-232 channel, the Commodore 64 receiver
buffer will hold up to 255 characters before the buffer overflows. This
is indicated in the RS-232 status word (ST in BASIC, or RSSTAT in machine
language). If an overflow occurs, then all characters received during a
full buffer condition, from that point on, are lost. Obviously, it pays
to keep the buffer as clear as possible.
If you wish to receive RS-232 data at high speeds (BASIC can only go so
fast, especially considering garbage collects. This can cause the re-
ceiver buffer to overflow), you will have to use machine language
routines to handle this type of data burst.
BASIC SYNTAX:
Recommended: GET#lfn, <string variable>
NOT Recommended: INPUT#lfn <variable list>
KERNAL ENTRIES:
CHKIN ($FFC6)-See Memory Map for more information on entry and exit
conditions.
GETIN ($FFE4)-See Memory Map for more information on entry and exit
conditions.
CHRIN ($FFCF)-See Memory Map for more information on entry and exit
conditions.
352 INPUT/OUTPUT GUIDE
~
+-----------------------------------------------------------------------+
| NOTES: |
| If the word length is less than 8 bits, all unused bit(s) will be |
| assigned a value of zero. |
| If a GET# does not find any data in the buffer, the character "" (a |
| null) is returned. |
| If INPUT# is used, then the system will hang in a waiting condition |
| until a non-null character and a following carriage return is |
| received. Therefore, if the Clear To Send (CTS) or Data Set Ready |
| (DSR) line(s) disappear during character INPUT#, the system will hang |
| in a RESTORE-only state. This is why the INPUT# and CHRIN routines are|
| NOT recommended. |
| The routine CHKIN handles the x-line handshake which follows the EIA|
| standard (August 1979) for RS-232-C interfaces. (The Request To Send |
| (RTS), CTS, and Received line signal (DCD) lines are implemented with |
| the Commodore 64 computer defined as the Data Terminal device.) |
+-----------------------------------------------------------------------+
SENDING DATA TO AN RS-232 CHANNEL
When sending data, the output buffer can hold 255 characters before a
full buffer hold-off occurs. The system will wait in the CHROUT routine
until transmission is allowed or the <RUN/STOP> and <RESTORE> keys are
used to recover the system through a WARM START.
BASIC SYNTAX:
CMD lfn-acts same as in the BASIC specifications.
PRINT#lfn,<variable list>
KERNAL ENTRIES:
CHKOUT ($FFC9)-See Memory Map for more information on entry and exit
conditions.
CHROUT ($FFD2)-See Memory Map for more information on entry conditions.
INPUT/OUTPUT GUIDE 353
~
+-----------------------------------------------------------------------+
| IMPORTANT NOTES: There is no carriage-return delay built into the |
| output channel. This means that a normal RS-232 printer cannot |
| correctly print, unless some form of hold-off (asking the Commodore 64|
| to wait) or internal buffering is implemented by the printer. The |
| hold-off can easily be implemented in your program. If a CTS (x-line) |
| handshake is implemented, the Commodore 64 buffer will fill, and then |
| hold-off more output until transmission is allowed by the RS-232 |
| device. X-line handshaking is a handshake routine that uses multi- |
| lines for receiving and transmitting data. |
| The routine CHKOUT handles the x-line handshake, which follows the |
| EIA standard (August 1979) for RS-232-C interfaces. The RTS, CTS, and |
| DCD lines are implemented with the Commodore 64 defined as the Data |
| Terminal Device. |
+-----------------------------------------------------------------------+
CLOSING AN RS-232 DATA CHANNEL
Closing an RS-232 file discards all data in the buffers at the time of
execution (whether or not it had been transmitted or printed out), stops
all RS-232 transmitting and receiving, sets the RTS and transmitted data
(Sout) lines high, and removes both RS-232 buffers.
BASIC SYNTAX:
CLOSE lfn
KERNAL ENTRY:
CLOSE ($FFC3)-See Memory Map for more information on entry and exit
conditions.
+-----------------------------------------------------------------------+
| NOTE: Care should be taken to ensure all data is transmitted before |
| closing the channel. A way to check this from BASIC is: |
| |
| 100 SS=ST: IF(SS=0 OR SS=8) THEN 100 |
| 110 CLOSE lfn |
+-----------------------------------------------------------------------+
354 INPUT/OUTPUT GUIDE
~
Table 6-1. User-Port Lines
+-----------------------------------------------------------------------+
| (6526 DEVICE #2 Loc. $DD00-$DD0F) |
+---+-----+----------------------+------+-------+-------+---------------+
|PIN| 6526| DESCRIPTION | EIA | ABV | IN/ | MODES |
| ID| ID | | | | OUT | |
+---+-----+----------------------+------+-------+-------+---------------+
| C | PB0 | RECEIVED DATA | (BB) | Sin | IN | 1 2 |
| D | PB1 | REQUEST TO SEND | (CA) | RTS | OUT | 1*2 |
| E | PB2 | DATA TERMINAL READY | (CD) | DTR | OUT | 1*2 |
| F | PB3 | RING INDICATOR | (CE) | RI | IN | 3 |
| H | PB4 | RECEIVED LINE SIGNAL | (CF) | DCD | IN | 2 |
| I | PB5 | UNASSIGNED | ( ) | XXX | IN | 3 |
| K | PB6 | CLEAR TO SEND | (CB) | CTS | IN | 2 |
| L | PB7 | DATA SET READY | (CC) | DSR | IN | 2 |
| | | | | | | |
| B |FLAG2| RECEIVED DATA | (BB) | Sin | IN | 1 2 |
| M | PA2 | TRANSMITTED DATA | (BA) | Sout | OUT | 1 2 |
| | | | | | | |
| A | GND | PROTECTIVE GROUND | (AA) | GND | | 1 2 |
| N | GND | SIGNAL GROUND | (AB) | GND | | 1 2 3 |
+---+-----+----------------------+------+-------+-------+---------------+
| MODES: |
| 1) 3-LINE INTERFACE (Sin,Sout,GND) |
| 2) X-LINE INTERFACE |
| 3) USER AVAILABLE ONLY (Unused/unimplemented in code.) |
| * These lines are held high during 3-LINE mode. |
+-----------------------------------------------------------------------+
+-----------------------------------------------------------------------+
| [7] [6] [5] [4] [3] [2] [1] [0] (Machine Lang.-RSSTAT |
| | | | | | | | +- PARITY ERROR BIT |
| | | | | | | +----- FRAMING ERROR BIT |
| | | | | | +--------- RECEIVER BUFFER OVERRUN BIT |
| | | | | +------------- RECEIVER BUFFER-EMPTY |
| | | | | (USE TO TEST AFTER A GET#) |
| | | | +----------------- CTS SIGNAL MISSING BIT |
| | | +--------------------- UNUSED BIT |
| | +------------------------- DSR SIGNAL MISSING BIT |
| +----------------------------- BREAK DETECTED BIT |
| |
+-----------------------------------------------------------------------+
Figure 6-3. RS-232 Status Register.
INPUT/OUTPUT GUIDE 355
~
+-----------------------------------------------------------------------+
| NOTES: |
| If the BIT=0, then no error has been detected. |
| The RS-232 status register can be read from BASIC using the variable|
| ST. |
| If ST is read by BASIC or by using the KERNAL READST routine the |
| RS-232 status word is cleared when you exit. If multiple uses of the |
| STATUS word are necessary the ST should be assigned to another |
| variable. For example: |
| |
| SR=ST: REM ASSIGNS ST TO SR |
| |
| The RS-232 status is read (and cleared) only when the RS-232 channel|
| was the last external I/O used. |
+-----------------------------------------------------------------------+
SAMPLE BASIC PROGRAMS
start tok64 page356.prg
10 rem this program sends and receives data to/from a silent 700
11 rem terminal modified for pet ascii
20 rem ti silent 700 set-up: 300 baud, 7-bit ascii, mark parity,
21 rem full duplex
30 rem same set-up at computer using 3-line interface
100 open2,2,3,chr$(6+32)+chr$(32+128):rem open the channel
110 get#2,a$:rem turn on the receiver channel (toss a null)
200 rem main loop
210 get b$:rem get from computer keyboard
220 if b$<>""then print#2,b$;:rem if a key pressed, send to terminal
230 get#2,c$:rem get a key from the terminal
240 print b$;c$;:rem print all inputs to computer screen
250 sr=st:ifsr=0orsr=8then200:rem check status, if good then continue
300 rem error reporting
310 print "error: ";
320 if sr and 1 then print"parity"
330 if sr and 2 then print"frame"
340 if sr and 4 then print"receiver buffer full"
350 if sr and 128 then print"break"
360 if (peek(673)and1)then360:rem wait until all chars transmitted
370 close 2:end
stop tok64
356 INPUT/OUTPUT GUIDE
~
start tok64 page357.prg
10 rem this program sends and receives true ascii data
100 open 5,2,3,chr$(6)
110 dim f%(255),t%(255)
200 for j=32 to 64:t%(j)=j:next
210 t%(13)=13:t%(20)=8:rv=18:ct=0
220 for j=65 to 90:k=j+32:t%=(j)=k:next
230 for j=91 to 95:t%(j)=j:next
240 for j=193 to 218:k=j-128:t%(j)=k:next
250 t%(146)=16:t%(133)=16
260 for j=0 to 255
270 k=t%(j)
280 if k<>0then f%(k)=j:f%(k+128)=j
290 next
300 print" "chr$(147)
310 get#5,a$
320 if a$=""or st<>0 then 360
330 print" "chr$(157);chr$(f%(asc(a$)));
340 if f%(asc(a$))=34 then poke212,0
350 goto310
360 printchr$(rv)" "chr$(157);chr$(146);:get a$
370 if a$<>""then print#5,chr$(t%(asc(a$)));
380 ct=ct+1
390 if ct=8 thenct=0:rv=164-rv
410 goto310
stop tok64
RECEIVER/TRANSMITTER BUFFER BASE LOCATION POINTERS
$00F7-REBUF-A two-byte pointer to the Receiver Buffer base location.
$00F9-ROBUF-A two-byte pointer to the Transmitter Buffer base location.
The two locations above are set up by the OPEN KERNAL routine, each
pointing to a different 256-byte buffer. They are de-allocated by writing
a zero into the high order bytes ($00F8 and $00FA), which is done by the
CLOSE KERNAL entry. They may also be allocated/de-allocated by the
machine language programmer for his/her own purposes, removing/creating
only the buffer(s) required. When using a machine language program that
allocates these buffers, care must be taken to make sure that the top of
memory pointers stay correct, especially if BASIC programs are expected
to run at the same time.
INPUT/OUTPUT GUIDE 357
~
ZERO-PAGE MEMORY LOCATIONS AND USAGE FOR
RS-232 SYSTEM INTERFACE
$00A7-INBIT-Receiver input bit temp storage.
$00A8-BITCI-Receiver bit count in.
$00A9-RINONE-Receiver flag Start bit check.
$00AA-RIDATA-Receiver byte buffer/assembly location.
$00AB-RIPRTY-Receiver parity bit storage.
$00B4-BITTS-Transmitter bit count out.
$00B5-NXTBIT-Transmitter next bit to be sent.
$00B6-RODATA-Transmitter byte buffer/disassembly location.
All the above zero-page locations are used locally and are only given
as a guide to understand the associated routines. These cannot be used
directly by the BASIC or KERNAL level programmer to do RS-232 type
things. The system RS-232 routines must be used.
NONZERO-PAGE MEMORY LOCATIONS AND USAGE FOR
RS-232 SYSTEM INTERFACE
General RS-232 storage:
$0293-M51CTR-Pseudo 6551 control register (see Figure 6-1).
$0294-M51COR-Pseudo 6551 command register (see Figure 6-2) .
$0295-M51AJB-Two bytes following the control and command registers in
the file name field. These locations contain the baud rate for
the start of the bit test during the interface activity, which,
in turn, is used to calculate baud rate.
$0297-RSSTAT-The RS-232 status register (see Figure 6-3).
$0298-BITNUM-The number of bits to be sent/received.
$0299-BAUDOF-Two bytes that are equal to the time of one bit cell.
(Based on system clock/baud rate.)
358 INPUT/OUTPUT GUIDE
~
$029B-RIDBE-The byte index to the end of the receiver FIFO buffer.
$029C-RIDBS-The byte index to the start of the receiver FIFO buffer.
$029D-RODBS-The byte index to the start of the transmitter FIFO buffer.
$029E-RODBE-The byte index to the end of the transmitter FIFO buffer.
$02A1-ENABL-Holds current active interrupts in the CIA #2 ICR.
When bit 4 is turned on means that the system is waiting for the
Receiver Edge. When bit 1 is turned on then the system is
receiving data. When bit 0 is turned on then the system is
transmitting data.
THE USER PORT
The user port is meant to connect the Commodore 64 to the outside
world. By using the lines available at this port, you can connect the
Commodore 64 to a printer, a Votrax Type and Talk, a MODEM, even another
computer.
The port on the Commodore 64 is directly connected to one of the 6526
CIA chips. By programming, the CIA will connect to many other devices.
PORT PIN DESCRIPTION
1 1 1
1 2 3 4 5 6 7 8 9 0 1 2
+--@-@-@-@-@-@-@-@-@-@-@-@--+
| |
+--@-@-@-@-@-@-@-@-@-@-@-@--+
A B C D E F H J K L M N
INPUT/OUTPUT GUIDE 359
~
PORT PIN DESCRIPTION
+-----------+-----------+-----------------------------------------------+
| PIN | | |
+-----------+DESCRIPTION| NOTES |
| TOP SIDE | | |
+-----------+-----------+-----------------------------------------------+
| 1 | GROUND | |
| 2 | +5V | (100 mA MAX.) |
| 3 | RESET | By grounding this pin, the Commodore 64 will |
| | | do a COLD START, resetting completely. The |
| | | pointers to a BASIC program will be reset, |
| | | but memory will not be cleared. This is also |
| | | a RESET output for the external devices. |
| 4 | CNT1 | Serial port counter from CIA#1(SEE CIA SPECS)|
| 5 | SP1 | Serial port from CIA #l (SEE 6526 CIA SPECS) |
| 6 | CNT2 | Serial port counter from CIA#2(SEE CIA SPECS)|
| 7 | SP2 | Serial port from CIA #l (SEE 6526 CIA SPECS) |
| 8 | PC2 | Handshaking line from CIA #2 (SEE CIA SPECS) |
| 9 |SERIAL ATN | This pin is connected to the ATN line of the |
| | | serial bus. |
| 10 |9 VAC+phase| Connected directly to the Commodore |
| 11 |9 VAC-phase| 64 transformer (50 mA MAX.). |
| 12 | GND | |
| | | |
|BOTTOM SIDE| | |
| | | |
| A | GND | The Commodore 64 gives you control over |
| B | FLAG2 | PORT B on CIA chip #1. Eight lines for input |
| C | PB0 | or output are available, as well as 2 lines |
| D | PB1 | for handshaking with an outside device. The |
| E | PB2 | I/O lines for PORT B are controlled by two |
| F | PB3 | locations. One is the PORT itself, and is |
| H | PB4 | located at 56577 ($DD01 HEX). Naturally you |
| I | PB5 | PEEK it to read an INPUT, or POKE it to set |
| K | PB6 | an OUTPUT. Each of the eight I/O lines can |
| L | PB7 | be set up as either an INPUT or an OUTPUT by |
| M | PA2 | by setting the DATA DIRECTION REGISTER |
| N | GND | properly. |
+-----------+-----------+-----------------------------------------------+
360 INPUT/OUTPUT GUIDE
~
The DATA DIRECTION REGISTER has its location at 56579 ($DD03 hex). Each
of the eight lines in the PORT has a BIT in the eight-bit DATA DIRECTION
REGISTER (DDR) which controls whether that line will be an input or an
output. If a bit in the DDR is a ONE, the corresponding line of the PORT
will be an OUTPUT. If a bit in the DDR is a ZERO, the corresponding line
of the PORT will be an INPUT. For example, if bit 3 of the DDR is set to
1, then line 3 of the PORT will be an output. A further example:
If the DDR is set like this:
BIT #: 7 6 5 4 3 2 1 0
VALUE: 0 0 1 1 1 0 0 0
You can see that lines 5,4, and 3 will be outputs since those bits are
ones. The rest of the lines will be inputs, since those lines are zeros.
To PEEK or POKE the USER port, it is necessary to use both the DDR and
the PORT itself.
Remember that the PEEK and POKE statements want a number from 0-255.
The numbers given in the example must be translated into decimal before
they can be used. The value would be:
2^5 + 2^4 + 2^3 = 32 + 16 + 8 = 56
Notice that the bit # for the DDR is the same number that = 2 raised to
a power to turn the bit value on.
(16 = 2^4=2*2*2*2, 8 = 2^3=2*2*2)
The two other lines, FLAG1 and PA2 are different from the rest of the
USER PORT. These two lines are mainly for HANDSHAKING, and are programmed
differently from port B.
Handshaking is needed when two devices communicate. Since one device
may run at a different speed than another device it is necessary to give
the devices some way of knowing what the other device is doing. Even when
the devices are operating at the same speed, handshaking is necessary to
let the other know when data is to be sent, and if it has been received.
The FLAG1 line has special characteristics which make it well suited for
handshaking.
FLAG1 is a negative edge sensitive input which can be used as a general
purpose interrupt input. Any negative transition on the FLAG line will
set the FLAG interrupt bit. If the FLAG interrupt is enabled, this will
INPUT/OUTPUT GUIDE 361
~
cause an INTERRUPT REQUEST. If the FLAG bit is not enabled, it can be
polled from the interrupt register under program control.
PA2 is bit 2 of PORT A of the CIA. It is controlled like any other bit
in the port. The port is located at 56576 ($DD00). The data direction
register is located at 56578 ($DD02.)
FOR MORE INFORMATION ON THE 6526 SEE THE CHIP SPECIFICATIONS IN
APPENDIX M.
THE SERIAL BUS
The serial bus is a daisy chain arrangement designed to let the Com-
modore 64 communicate with devices such as the VIC-1541 DISK DRIVE and
the VIC-1525 GRAPHICS PRINTER. The advantage of the serial bus is that
more than one device can be connected to the port. Up to 5 devices can be
connected to the serial bus at one time.
There are three types of operation over a serial bus-CONTROL, TALK, and
LISTEN. A CONTROLLER device is one which controls operation of the serial
bus. A TALKER transmits data onto the bus. A LISTENER receives data from
the bus.
The Commodore 64 is the controller of the bus. It also acts as a TALKER
(when sending data to the printer, for example) and as a LISTENER (when
loading a program from the disk drive, for example). Other devices may be
either LISTENERS (the printer), TALKERS, or both (the disk drive). Only
the Commodore 64 can act as the controller.
All devices connected on the serial bus will receive all the data
transmitted over the bus. To allow the Commodore 64 to route data to its
intended destination, each device has a bus ADDRESS. By using this device
address, the Commodore 64 can control access to the bus. Addresses on the
serial bus range from 4 to 31.
The Commodore 64 can COMMAND a particular device to TALK or LISTEN.
When the Commodore 64 commands a device to TALK, the device will begin
putting data onto the serial bus. When the Commodore 64 commands a device
to LISTEN, the device addressed will get ready to receive data (from the
Commodore 64 or from another device on the bus). Only one device can TALK
on the bus at a time; otherwise, the data will collide and the system
will crash in confusion. However, any number of devices can LISTEN at the
same time to one TALKER.
362 INPUT/OUTPUT GUIDE
~
COMMON SERIAL BUS ADDRESSES
+--------+--------------------------+
| NUMBER | DEVICE |
+--------+--------------------------+
| 4 or 5 | VIC-1525 GRAPHIC PRINTER |
| 8 | VIC-1541 DISK DRIVE |
+--------+--------------------------+
Other device addresses are possible. Each device has its own address.
Certain devices (like the Commodore 64 printer) provide a choice between
two addresses for the convenience of the user.
The SECONDARY ADDRESS is to let the Commodore 64 transmit setup
information to a device. For example, to OPEN a connection on the bus to
the printer, and have it print in UPPER/LOWER case, use the following
OPEN 1,4,7
where,
1 is the logical file number (the number you PRINT# to),
4 is the ADDRESS of the printer, and
7 is the SECONDARY ADDRESS that tells the printer to go into UPPER/
LOWER case mode.
There are 6 lines used in serial bus operations - input and 3 output.
The 3 input lines bring data, control, and timing signals into the Com-
modore 64. The 3 output lines send data, control, and timing signals from
the Commodore 64 to external devices on the serial bus.
Serial I/O
++ ++
+-------+----------------------+ / +-+ \
| Pin | Type | /5 1\
+-------+----------------------+ + O O +
| 1 | /SERIAL SRQ IN | | 6 |
| 2 | GND | | O |
| 3 | SERIAL ATN OUT | | |
| 4 | SERIAL CLK IN/OUT | + O O +
| 5 | SERIAL DATA IN/OUT | \4 O 2/
| 6 | /RESET | \ 3 /
+-------+----------------------+ +---+
INPUT/OUTPUT GUIDE 363
~
SERIAL SRQ IN: (SERIAL SERVICE REQUEST IN)
Any device on the serial bus can bring this signal LOW when it requires
attention from the Commodore 64. The Commodore 64 will then take care of
the device. (See Figure 6-4).
[THE PICTURE IS MISSING!]
Figure 6-4. Serial Bus Timing.
364 INPUT/OUTPUT GUIDE
~
SERIAL ATN OUT: (SERIAL ATTENTION OUT)
The Commodore 64 uses this signal to start a command sequence for a
device on the serial bus. When the Commodore 64 brings this signal LOW,
all other devices on the bus start listening for the Commodore 64 to
transmit an address. The device addressed must respond in a preset period
of time; otherwise, the Commodore 64 will assume that the device
addressed is not on the bus, and will return an error in the STATUS WORD.
(See Figure 6-4).
[THE PICTURE IS MISSING!]
SERIAL BUS TIMING
+-----------------------------+-------+-------+-------+-----------------+
| Description | Symbol| Min. | Typ. | Max. |
+-----------------------------+-------+-------+-------+-----------------+
| ATN RESPONSE (REQUIRED) (1) | Tat | - | - | 1000us |
| LISTENER HOLD-OFF | Th | 0 | - | infinite |
| NON-EOI RESPONSE TO RFD (2) | Tne | - | 40us | 200us |
| BIT SET-UP TALKER (4) | Ts | 20us | 70us | - |
| DATA VALID | Tv | 20us | 20us | - |
| FRAME HANDSHAKE (3) | Tf | 0 | 20 | 1000us |
| FRAME TO RELEASE OF ATN | Tr | 20us | - | - |
| BETWEEN BYTES TIME | Tbb | 100us | - | - |
| EOI RESPONSE TIME | Tye | 200us | 250us | - |
| EOI RESPONSE HOLD TIME (5) | Tei | 60us | - | - |
| TALKER RESPONSE LIMIT | Try | 0 | 30us | 60us |
| BYTE-ACKNOWLEDGE (4) | Tpr | 20us | 30us | - |
| TALK-ATTENTION RELEASE | Ttk | 20us | 30us | 100us |
| TALK-ATTENTION ACKNOWLEDGE | Tdc | 0 | - | - |
| TALK-ATTENTION ACK. HOLD | Tda | 80us | - | - |
| EOI ACKNOWLEDGE | Tfr | 60us | - | - |
+-----------------------------+-------+-------+-------+-----------------+
Notes:
1. If maximum time exceeded, device not present error.
2. If maximum time exceeded, EOI response required.
3. If maximum time exceeded, frame error.
4. Tv and Tpr minimum must be 60us for external device to be a talker.
5. Tei minimum must be 80us for external device to be a listener.
INPUT/OUTPUT GUIDE 365
~
SERIAL CLK IN/OUT: (SERIAL CLOCK IN/OUT)
This signal is used for timing the data sent on the serial bus. (See
Figure 6-4).
SERIAL DATA IN/OUT:
Data on the serial bus is transmitted one bit at a time on this line.
(See Figure 6-4.)
THE EXPANSION PORT
The expansion connector is a 44-pin (22122) female edge connector on
the back of the Commodore 64. With the Commodore 64 facing you, the
expansion connector is on the far right of the back of the computer. To
use the connector, a 44-pin (22/22) male edge connector is required.
This port is used for expansions of the Commodore 64 system which
require access to the address bus or the data bus of the computer.
Caution is necessary when using the expansion bus, because it's possible
to damage the Commodore 64 by a malfunction of your equipment.
The expansion bus is arranged as follows:
2 2 2 1 1 1 1 1 1 1 1 1 1
2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1
+---@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@---+
| |
+---@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@---+
Z Y X W V U T S R P N M L K J H F E D C B A
The signals available on the connector are as follows:
+---------+---+---------------------------------------------------------+
| NAME |PIN| DESCRIPTION |
+---------+---+---------------------------------------------------------+
| GND | 1 | System ground |
| +5VDC | 2 | (Total USER PORT and CARTRIDGE devices can |
| +5VDC | 3 | draw no more than 450 mA.) |
| /IRQ | 4 | Interrupt Request line to 6502 (active low) |
| R/W | 5 | Read/Write (write active low) |
|DOT CLOCK| 6 | 8.18 MHz video dot clock |
| /I/O1 | 7 | I/O block 1 @ $ DE00-$DEFF (active low) unbuffered I/O |
| /GAME | 8 | active low ls ttl input |
| /EXROM | 9 | active low ls ttl input |
| /I/O2 |10 | I/O block 2 @ $DF00-$DFFF (active low) buff'ed ls ttl |
output |
366 INPUT/OUTPUT GUIDE
~
+---------+---+---------------------------------------------------------+
| NAME |PIN| DESCRIPTION |
+---------+---+---------------------------------------------------------+
| /ROML |11 | 8K decoded RAM/ROM block @ $8000 (active low) buffered |
| | | ls ttl output |
| BA |12 | Bus available signal from the VIC-II chip unbuffered |
| | | 1 Is load max. |
| /DMA |13 | Direct memory access request line (active low input) |
| | | ls ttl input |
| D7 |14 | Data bus bit 7 \ |
| D6 |15 | Data bus bit 6 + |
| D5 |16 | Data bus bit 5 | |
| D4 |17 | Data bus bit 4 +- unbuffered, 1 ls ttl load max |
| D3 |18 | Data bus bit 3 +- |
| D2 |19 | Data bus bit 2 | |
| D1 |20 | Data bus bit 1 + |
| D0 |21 | Data bus bit 0 / |
| GND |22 | System ground |
| GND | A | |
| /ROMH | B | 8K decoded RAM/ROM block @ $E000 buffered |
| /RESET | C | 6502 RESET pin(active low) buff'ed ttl out/unbuff'ed in|
| /NMI | D | 6502 Non Maskable Interrupt (active low) buff'ed ttl |
| | | out, unbuff'ed in |
| 02 | E | Phase 2 system clock |
| A15 | F | Address bus bit 15 \ |
| A14 | H | Address bus bit 14 + |
| A13 | J | Address bus bit 13 | |
| A12 | K | Address bus bit 12 | |
| A11 | L | Address bus bit 11 | |
| A10 | M | Address bus bit 10 | |
| A9 | N | Address bus bit 9 | |
| A8 | P | Address bus bit 8 +-- unbuffered, 1 ls ttl load max |
| A7 | R | Address bus bit 7 +-- |
| A6 | S | Address bus bit 6 | |
| A5 | T | Address bus bit 5 | |
| A4 | U | Address bus bit 4 | |
| A3 | V | Address bus bit 3 | |
| A2 | W | Address bus bit 2 | |
| A1 | X | Address bus bit 1 + |
| A0 | Y | Address bus bit 0 / |
| GND | Z | System ground |
+---------+---+---------------------------------------------------------+
INPUT/OUTPUT GUIDE 367
~
Following is a description of some important fines on the expansion
port:
Pins 1,22,A,Z are connected to the system ground.
Pin 6 is the DOT CLOCK. This is the 8.18-MHz video dot clock. All
system timing is derived from this clock.
Pin 12 is the BA (BUS AVAILABLE) signal from the VIC-II chip. This line
will go low 3 cycles before the VIC-II takes over the system busses, and
remains low until the VIC-II is finished fetching display information.
Pin 13 is the DMA (DIRECT MEMORY ACCESS) line. When this line is pulled
low, the address bus, the data bus, and the Read/Write line of the 6510
processor chip enter high-impedance state mode. This allows an external
processor to take control of the system busses. This line should only be
pulled low when the (02 clock is low. Also, since the VIC-II chip will
continue to perform display DMA, the external device must conform to the
VIC-II timing. (See VIC-II timing diagram.) This line is pulled up on the
Commodore 64.
Z-80 MICROPROCESSOR CARTRIDGE
Reading this book and using your computer has shown you just how
versatile your Commodore 64 really is. But what makes this machine even
more capable of meeting your needs is the addition of peripheral
equipment. Peripherals are things like Datassette(TM) recorders, disk
drives, printers, and modems. All these items can be added to your
Commodore 64 through the various ports and sockets on the back of your
machine. The thing that makes Commodore peripherals so good is the fact
that our peripherals are "intelligent." That means that they don't take
up valuable Random Access Memory space when they're in use. You're free
to use all 64K of memory in your Commodore 64.
Another advantage of your Commodore 64 is the fact most programs you
write on your Commodore 64 today will be upwardly compatible with any new
Commodore computer you buy in the future. This is partially because of
the qualities of the computer's Operating System (OS).
However, there is one thing that the Commodore OS can't do: make your
programs compatible with a computer made by another company.
368 INPUT/OUTPUT GUIDE
~
Most of the time you won't even have to think about using another com-
pany's computer, because your Commodore 64 is so easy to use. But for the
occasional user who wants to take advantage of software that may not be
available in Commodore 64 format we have created a Commodore CP/M(R)
cartridge.
CP/M(R) is not a "computer dependent" operating system. Instead it uses
some of the memory space normally available for programming to run its
own operating system. There are advantages and disadvantages to this. The
disadvantages are that the programs you write will have to be shorter
than the programs you can write using the Commodore 64's built-in
operating system. In addition, you can NOT use the Commodore 64's
powerful screen editing capabilities. The advantages are that you can now
use a large amount of software that has been specifically designed for
CP/M(R) and the Z-80 microprocessor, and the programs that you write
using the CP/M(R) operating system can be transported and run on any
other computer that has CP/M(R) and a Z-80 card.
By the way, most computers that have a Z-80 microprocessor require that
you go inside the computer to actually install a Z-80 card. With this
method you have to be very careful not to disturb the delicate circuitry
that runs the rest of the computer. The Commodore CP/M& cartridge
eliminates this hassle because our Z-80 cartridge plugs into the back of
your Commodore 64 quickly and easily, without any messy wires that can
cause problems later.
USING COMMODORE CP/M(R)
The Commodore Z-80 cartridge let's you run programs designed for a Z-80
microprocessor on your Commodore 64. The cartridge is provided with a
diskette containing the Commodore CP/M(R) operating system.
RUNNING COMMODORE CP/M(R)
To run CP/M(R):
1) LOAD the CP/M(R) program from your disk drive.
2) Type RUN.
3) Hit the <RETURN> key.
INPUT/OUTPUT GUIDE 369
~
At this point the 64K bytes of RAM in the Commodore 64 are accessible
by the built-in 6510 central processor, OR 48K bytes of RAM are available
for the Z-80 central processor. You can shift back and forth between
these two processors, but you can NOT use them at the same time in a
single program. This is possible because of your Commodore 64's
sophisticated timing mechanism.
Below is the memory address translation that is performed on the Z-80
cartridge. You should notice that by adding 4096 bytes to the memory
locations used in CP/M(R) $1000 (hex) you equal the memory addresses of
the normal Commodore 64 operating system. The correspondence between Z-80
and 6510 memory addresses is as follows:
+-----------------------------------+-----------------------------------+
| Z-80 ADDRESSES | 6510 ADDRESSES |
+-----------------+-----------------+-----------------+-----------------+
| DECIMAL | HEX | DECIMAL | HEX |
+-----------------+-----------------+-----------------+-----------------+
| 0000-4095 | 0000-0FFF | 4096-8191 | 1000-1FFF |
| 4096-8191 | 1000-1FFF | 8192-12287 | 2000-2FFF |
| 8192-12287 | 2000-2FFF | 12288-16383 | 3000-3FFF |
| 12288-16383 | 3000-3FFF | 16384-20479 | 4000-4FFF |
| 16384-20479 | 4000-4FFF | 20480-24575 | 5000-5FFF |
| 20480-24575 | 5000-5FFF | 24576-28671 | 6000-6FFF |
| 24576-28671 | 6000-6FFF | 28672-32767 | 7000-7FFF |
| 28672-32767 | 7000-7FFF | 32768-36863 | 8000-SFFF |
| 32768-36863 | 8000-8FFF | 36864-40959 | 9000-9FFF |
| 36864-40959 | 9000-9FFF | 40960-45055 | A000-AFFF |
| 40960-45055 | A000-AFFF | 45056-49151 | B000-BFFF |
| 45056-49151 | B000-BFFF | 49152-53247 | C000-CFFF |
| 49152-53247 | C000-CFFF | 53248-57343 | D000-DFFF |
| 53248-57343 | D000-DFFF | 57344-61439 | E000-EFFF |
| 57344-61439 | E000-EFFF | 61440-65535 | F000-FFFF |
| 61440-65535 | F000-FFFF | 0000-4095 | 0000-0FFF |
+-----------------+-----------------+-----------------+-----------------+
370 INPUT/OUTPUT GUIDE
~
To TURN ON the Z-80 and TURN OFF the 6510 chip, type in the following
program:
start tok64 page371.prg
10 rem this program is to be used with the z80 card
20 rem it first stores z80 data at $1000 (Z80=$0000)
30 rem then it turns off the 6510 irq's and enables
40 rem the z80 card. the z80 card must be turned off
50 rem to reenable the 6510 system.
100 rem store z80 data
110 read b: rem get size of z80 code to be moved
120 for i=4096 to 4096+b-1:rem move code
130 read a:poke i,a
140 next i
200 rem run z80 code
210 poke 56333,127: rem turn of 6510 irq's
220 poke 56832,00 : rem turn on z80 card
230 poke 56333,129: rem turn on 6510 irq's when z80 done
240 end
1000 rem z80 machine language code data section
1010 data 18 : rem size of data to be passed
1100 rem z80 turn on code
1110 data 00,00,00 : rem our z80 card requires turn on time at $0000
1200 rem z80 task data here
1210 data 33,02,245: rem ld hl,nn (location on screen)
1220 data 52 : rem inc hl (increment that location)
1300 rem z80 self-turn off data here
1310 data 62,01 : rem ld a,n
1320 data 50,00,206 : rem ld (nn),a :i/o location
1330 data 00,00,00 : rem nop, nop, nop
1340 data 195,00,00 : rem jmp $0000
stop tok64
For more details about Commodore CP/M(R) and the Z-80 microprocessor
look for the cartridge and the Z-80 Reference Guide at your local
Commodore computer dealer.
INPUT/OUTPUT GUIDE 371
~~
APPENDICES
373
~
APPENDIX A
ABBREVIATIONS FOR BASIC KEYWORDS
As a time-saver when typing in programs and commands, Commodore 64
BASIC allows the user to abbreviate most keywords. The abbreviation for
PRINT is a question mark. The abbreviations for other words are made by
typing the first one or two letters of the word, followed by the SHIFTed
next letter of the word. If the abbreviations are used in a program line,
the keyword will LIST in the full form.
Looks like | Looks like
Command Abbreviation this on screen | Command Abbreviation this on screen
------------------------------------+------------------------------------
ABS A <SHIFT+B> | END E <SHIFT+N>
|
AND A <SHIFT+N> | EXP E <SHIFT+X>
|
ASC A <SHIFT+S> | FN NONE FN
|
ATN A <SHIFT+T> | FOR F <SHIFT+O>
|
CHR$ C <SHIFT+H> | FRE F <SHIFT+R>
|
CLOSE CL <SHIFT+O> | GET G <SHIFT+E>
|
CLR C <SHIFT+L> | GET# NONE GET#
|
CMD C <SHIFT+M> | GOSUB GO <SHIFT+S>
|
CONT C <SHIFT+O> | GOTO G <SHIFT+O>
|
COS NONE COS | IF NONE IF
|
DATA D <SHIFT+A> | INPUT NONE INPUT
|
DEF D <SHIFT+E> | INPUT# I <SHIFT+N>
|
DIM D <SHIFT+I> | INT NONE INT
|
LEFT$ LE <SHIFT+F> | RIGHT$ R <SHIFT+I>
|
LEN NONE LEN | RND R <SHIFT+N>
374 APPENDIX A
~
Looks like | Looks like
Command Abbreviation this on screen | Command Abbreviation this on screen
------------------------------------+------------------------------------
LET L <SHIFT+E> | RUN R <SHIFT+U>
|
LIST L <SHIFT+I> SAVE | SAVE S <SHIFT+A>
|
LOAD L <SHIFT+O> | SGN S <SHIFT+G>
|
LOG NONE LOG | SIN S <SHIFT+I>
|
MID$ M <SHIFT+I> | SPC( S <SHIFT+P>
|
NEW NONE NEW | SQR S <SHIFT+Q>
|
NEXT N <SHIFT+E> | STATUS ST ST
|
NOT N <SHIFT+O> | STEP ST <SHIFT+E>
|
ON NONE ON | STOP S <SHIFT+T>
|
OPEN O <SHIFT+P> | STR$ ST <SHIFT+R>
|
OR NONE OR | SYS S <SHIFT+Y>
|
PEEK P <SHIFT+E> | TAB( T <SHIFT+A>
|
POKE P <SHIFT+O> | TAN NONE TAN
|
POS NONE POS | THEN T <SHIFT+H>
|
PRINT ? ? | TIME TI TI
|
PRINT# P <SHIFT+R> | TIME$ TI$ TI$
|
READ R <SHIFT+E> | USR U <SHIFT+S>
|
REM NONE REM | VAL V <SHIFT+A>
|
RESTORE RE <SHIFT+S> | VERIFY V <SHIFT+E>
|
RETURN RE <SHIFT+T> | WAIT W <SHIFT+A>
APPENDIX A 375
~
APPENDIX B
SCREEN DISPLAY CODES
The following chart lists all of the characters built into the
Commodore 64 character sets. It shows which numbers should be POKED into
screen memory (locations 1024-2023) to get a desired character. Also
shown is which character corresponds to a number PEEKed from the screen.
Two character sets are available, but only one set at a time. This
means that you cannot have characters from one set on the screen at the
same time you have characters from the other set displayed. The sets are
switched by holding down the <SHIFT> and <C=> keys simultaneously.
From BASIC, POKE 53272,21 will switch to upper case mode and
POKE 53272,23 switches to lower case.
Any number on the chart may also be displayed in REVERSE. The reverse
character code may be obtained by adding 128 to the values shown.
If you want to display a solid circle at location 1504, POKE the code
for the circle (81) into location 1504: POKE 1504,81.
There is a corresponding memory location to control the color of each
character displayed on the screen (locations 55296-56295). To change the
color of the circle to yellow (color code 7) you would POKE the corre-
sponding memory location (55776) with the character color: POKE 55776,7.
Refer to Appendix D for the complete screen and color memory maps,
along with color codes.
+-----------------------------------------------------------------------+
| NOTE: The following POKEs display the same symbol in set 1 and 2: 1, |
| 27-64, 91-93, 96-104, 106-121, 123-127. |
+-----------------------------------------------------------------------+
SCREEN CODES
SET 1 SET 2 POKE | SET 1 SET 2 POKE | SET 1 SET 2 POKE
------------------------+------------------------+-----------------------
| |
@ 0 | C c 3 | F f 6
A a 1 | D d 4 | G g 7
B b 2 | E e 5 | H h 8
376 APPENDIX B
~
SET 1 SET 2 POKE | SET 1 SET 2 POKE | SET 1 SET 2 POKE
------------------------+------------------------+-----------------------
| |
I i 9 | % 37 | A 65
J j 10 | & 38 | B 66
K k 11 | ' 39 | C 67
L l 12 | ( 40 | D 68
M m 13 | ) 41 | E 69
N n 14 | * 42 | F 70
O o 15 | + 43 | G 71
P p 16 | , 44 | H 72
Q q 17 | - 45 | I 73
R r 18 | . 46 | J 74
S s 19 | / 47 | K 75
T t 20 | 0 48 | L 76
U u 21 | 1 49 | M 77
V v 22 | 2 50 | N 78
W w 23 | 3 51 | O 79
X x 24 | 4 52 | P 80
Y y 25 | 5 53 | Q 81
Z z 26 | 6 54 | R 82
[ 27 | 7 55 | S 83
pound 28 | 8 56 | T 84
] 29 | 9 57 | U 85
^ 30 | : 58 | V 86
<- 31 | ; 59 | W 87
SPACE 32 | < 60 | X 88
! 33 | = 61 | Y 89
" 34 | > 62 | Z 90
# 35 | ? 63 | 91
$ 36 | 64 | 92
APPENDIX B 377
~
SET 1 SET 2 POKE | SET 1 SET 2 POKE | SET 1 SET 2 POKE
------------------------+------------------------+-----------------------
| |
93 | 105 | 117
94 | 106 | 118
95 | 107 | 119
SPACE 96 | 108 | 120
97 | 109 | 121
98 | 110 | 122
99 | 111 | 123
100 | 112 | 124
101 | 113 | 125
102 | 114 | 126
103 | 115 | 127
104 | 116 |
Codes from 128-255 are reversed images of codes 0-127.
378 APPENDIX B
~
APPENDIX C
ASCII AND CHR$ CODES
This appendix shows you what characters will appear if you PRINT
CHR$(X), for all possible values of X. It will also show the values ob-
tained by typing PRINT ASC("x"), where x is any character you can type.
This is useful in evaluating the character received in a GET statement,
converting upper/lower case, and printing character based commands (like
switch to upper/lower case) that could not be enclosed in quotes.
+-----------------+-----------------+-----------------+-----------------+
| PRINTS CHR$ | PRINTS CHR$ | PRINTS CHR$ | PRINTS CHR$ |
+-----------------+-----------------+-----------------+-----------------+
| 0 | {down} 17 | " 34 | 3 51 |
| 1 | {rvs on} 18 | # 35 | 4 52 |
| 2 | {home} 19 | $ 36 | 5 53 |
| 3 | {del} 20 | % 37 | 6 54 |
| 4 | 21 | & 38 | 7 55 |
| {white} 5 | 22 | ' 39 | 8 56 |
| 6 | 23 | ( 40 | 9 57 |
| 7 | 24 | ) 41 | : 58 |
| disSHIFT+C= 8 | 25 | * 42 | ; 59 |
| enaSHIFT+C= 9 | 26 | + 43 | < 60 |
| 10 | 27 | , 44 | = 61 |
| 11 | {red} 28 | - 45 | > 62 |
| 12 | {right} 29 | . 46 | ? 63 |
| return 13 | {green} 30 | / 47 | @ 64 |
| lower case 14 | {blue} 31 | 0 48 | A 65 |
| 15 | SPACE 32 | 1 49 | B 66 |
| 16 | ! 33 | 2 50 | C 67 |
APPENDIX C 379
~
+-----------------+-----------------+-----------------+-----------------+
| PRINTS CHR$ | PRINTS CHR$ | PRINTS CHR$ | PRINTS CHR$ |
+-----------------+-----------------+-----------------+-----------------+
| D 68 | 97 | 126 | {grey 3} 155 |
| E 69 | 98 | 127 | {purple} 156 |
| F 70 | 99 | 128 | {left} 157 |
| G 71 | 100 | {orange} 129 | {yellow} 158 |
| H 72 | 101 | 130 | {cyan} 159 |
| I 73 | 102 | 131 | SPACE 160 |
| J 74 | 103 | 132 | 161 |
| K 75 | 104 | f1 133 | 162 |
| L 76 | 105 | f3 134 | 163 |
| M 77 | 106 | f5 135 | 164 |
| N 78 | 107 | f7 136 | 165 |
| O 79 | 108 | f2 137 | 166 |
| P 80 | 109 | f4 138 | 167 |
| Q 81 | 110 | f6 139 | 168 |
| R 82 | 111 | f8 140 | 169 |
| S 83 | 112 |shift+ret. 141 | 170 |
| T 84 | 113 |upper case 142 | 171 |
| U 85 | 114 | 143 | 172 |
| V 86 | 115 | {black} 144 | 173 |
| W 87 | 116 | {up} 145 | 174 |
| X 88 | 117 | {rvs off} 146 | 175 |
| Y 89 | 118 | {clear} 147 | 176 |
| Z 90 | 119 | {inst} 148 | 177 |
| [ 91 | 120 | {brown} 149 | 178 |
| pound 92 | 121 | {lt. red} 150 | 179 |
| ] 93 | 122 | {grey 1} 151 | 180 |
| ^ 94 | 123 | {grey 2} 152 | 181 |
|{arrow left}95 | 124 | {lt.green}153 | 182 |
| 96 | 125 | {lt.blue} 154 | 183 |
380 APPENDIX C
~
+-----------------+-----------------+-----------------+-----------------+
| PRINTS CHR$ | PRINTS CHR$ | PRINTS CHR$ | PRINTS CHR$ |
+-----------------+-----------------+-----------------+-----------------+
| 184 | 186 | 188 | 190 |
| 185 | 187 | 189 | 191 |
+-----------------+-----------------+-----------------+-----------------+
CODES 192-223 SAME AS 96-127
CODES 224-254 SAME AS 160-190
CODE 255 SAME AS 126
APPENDIX C 381
~
APPENDIX D
SCREEN AND COLOR MEMORY MAPS
The following charts list which memory locations control placing char-
acters on the screen, and the locations used to change individual char-
acter colors, as well as showing character color codes.
SCREEN MEMORY MAP
COLUMN 1063
0 10 20 30 39 /
+------------------------------------------------------------/
1024 | | 0
1064 | |
1104 | |
1144 | |
1184 | |
1224 | |
1264 | |
1304 | |
1344 | |
1384 | |
1424 | | 10
1464 | |
1504 | | ROW
1544 | |
1584 | |
1624 | |
1664 | |
1704 | |
1744 | |
1784 | |
1824 | | 20
1864 | |
1904 | |
1944 | |
1984 | | 24
+------------------------------------------------------------\
\
2023
382 APPENDIX D
~
The actual values to POKE into a color memory location to change a
character's color are:
0 BLACK 4 PURPLE 8 ORANGE 12 GRAY 2
1 WHITE 5 GREEN 9 BROWN 13 Light GREEN
2 RED 6 BLUE 10 Light RED 14 Light BLUE
3 CYAN 7 YELLOW 11 GRAY 1 15 GRAY 3
For example, to change the color of a character located at the upper
left-hand corner of the screen to red, type: POKE 55296,2.
COLOR MEMORY MAP
COLUMN 55335
0 10 20 30 39 /
+------------------------------------------------------------/
55296| | 0
55336| |
55376| |
55416| |
55456| |
55496| |
55536| |
55576| |
55616| |
55656| |
55696| | 10
55736| |
55776| | ROW
55816| |
55856| |
55896| |
55936| |
55976| |
56016| |
56056| |
56096| | 20
56136| |
56176| |
56216| |
56256| | 24
+------------------------------------------------------------\
56295
APPENDIX D 383
~
APPENDIX E
MUSIC NOTE VALUES
This appendix contains a complete list of Note#, actual note, and the
values to be POKED into the HI FREQ and LOW FREQ registers of the sound
chip to produce the indicated note.
+-----------------------------+-----------------------------------------+
| MUSICAL NOTE | OSCILLATOR FREQ |
+-------------+---------------+-------------+-------------+-------------+
| NOTE | OCTAVE | DECIMAL | HI | LOW |
+-------------+---------------+-------------+-------------+-------------+
| 0 | C-0 | 268 | 1 | 12 |
| 1 | C#-0 | 284 | 1 | 28 |
| 2 | D-0 | 301 | 1 | 45 |
| 3 | D#-0 | 318 | 1 | 62 |
| 4 | E-0 | 337 | 1 | 81 |
| 5 | F-0 | 358 | 1 | 102 |
| 6 | F#-0 | 379 | 1 | 123 |
| 7 | G-0 | 401 | 1 | 145 |
| 8 | G#-0 | 425 | 1 | 169 |
| 9 | A-0 | 451 | 1 | 195 |
| 10 | A#-0 | 477 | 1 | 221 |
| 11 | B-0 | 506 | 1 | 250 |
| 16 | C-1 | 536 | 2 | 24 |
| 17 | C#-1 | 568 | 2 | 56 |
| 18 | D-1 | 602 | 2 | 90 |
| 19 | D#-1 | 637 | 2 | 125 |
| 20 | E-1 | 675 | 2 | 163 |
| 21 | F-1 | 716 | 2 | 204 |
| 22 | F#-1 | 758 | 2 | 246 |
| 23 | G-1 | 803 | 3 | 35 |
| 24 | G#-1 | 851 | 3 | 83 |
| 25 | A-1 | 902 | 3 | 134 |
| 26 | A#-1 | 955 | 3 | 187 |
| 27 | B-1 | 1012 | 3 | 244 |
| 32 | C-2 | 1072 | 4 | 48 |
384 APPENDIX E
~
+-----------------------------+-----------------------------------------+
| MUSICAL NOTE | OSCILLATOR FREQ |
+-------------+---------------+-------------+-------------+-------------+
| NOTE | OCTAVE | DECIMAL | HI | LOW |
+-------------+---------------+-------------+-------------+-------------+
| 33 | C#-2 | 1136 | 4 | 112 |
| 34 | D-2 | 1204 | 4 | 180 |
| 35 | D#-2 | 1275 | 4 | 251 |
| 36 | E-2 | 1351 | 5 | 71 |
| 37 | F-2 | 1432 | 5 | 152 |
| 38 | F#-2 | 1517 | 5 | 237 |
| 39 | G-2 | 1607 | 6 | 71 |
| 40 | G#-2 | 1703 | 6 | 167 |
| 41 | A-2 | 1804 | 7 | 12 |
| 42 | A#-2 | 1911 | 7 | 119 |
| 43 | B-2 | 2025 | 7 | 233 |
| 48 | C-3 | 2145 | 8 | 97 |
| 49 | C#-3 | 2273 | 8 | 225 |
| 50 | D-3 | 2408 | 9 | 104 |
| 51 | D#-3 | 2551 | 9 | 247 |
| 52 | E-3 | 2703 | 10 | 143 |
| 53 | F-3 | 2864 | 11 | 48 |
| 54 | F#-3 | 3034 | 11 | 218 |
| 55 | G-3 | 3215 | 12 | 143 |
| 56 | G#-3 | 3406 | 13 | 78 |
| 57 | A-3 | 3608 | 14 | 24 |
| 58 | A#-3 | 3823 | 14 | 239 |
| 59 | B-3 | 4050 | 15 | 210 |
| 64 | C-4 | 4291 | 16 | 195 |
| 65 | C#-4 | 4547 | 17 | 195 |
| 66 | D-4 | 4817 | 18 | 209 |
| 67 | D#-4 | 5103 | 19 | 239 |
| 68 | E-4 | 5407 | 21 | 31 |
| 69 | F-4 | 5728 | 22 | 96 |
| 70 | F#-4 | 6069 | 23 | 181 |
| 71 | G-4 | 6430 | 25 | 30 |
| 72 | G#-4 | 6812 | 26 | 156 |
| 73 | A-4 | 7217 | 28 | 49 |
| 74 | A#-4 | 7647 | 29 | 223 |
| 75 | B-4 | 8101 | 31 | 165 |
| 80 | C-5 | 8583 | 33 | 135 |
| 81 | C#-5 | 9094 | 35 | 134 |
APPENDIX E 385
~
+-----------------------------+-----------------------------------------+
| MUSICAL NOTE | OSCILLATOR FREQ |
+-------------+---------------+-------------+-------------+-------------+
| NOTE | OCTAVE | DECIMAL | HI | LOW |
+-------------+---------------+-------------+-------------+-------------+
| 82 | D-5 | 9634 | 37 | 162 |
| 83 | D#-5 | 10207 | 39 | 223 |
| 84 | E-5 | 10814 | 42 | 62 |
| 85 | F-5 | 11457 | 44 | 193 |
| 86 | F#-5 | 12139 | 47 | 107 |
| 87 | G-5 | 12860 | 50 | 60 |
| 88 | G#-5 | 13625 | 53 | 57 |
| 89 | A-5 | 14435 | 56 | 99 |
| 90 | A#-5 | 15294 | 59 | 190 |
| 91 | B-5 | 16203 | 63 | 75 |
| 96 | C-6 | 17167 | 67 | 15 |
| 97 | C#-6 | 18188 | 71 | 12 |
| 98 | D-6 | 19269 | 75 | 69 |
| 99 | D#-6 | 20415 | 79 | 191 |
| 100 | E-6 | 21629 | 84 | 125 |
| 101 | F-6 | 22915 | 89 | 131 |
| 102 | F#-6 | 24278 | 94 | 214 |
| 103 | G-6 | 25721 | 100 | 121 |
| 104 | G#-6 | 27251 | 106 | 115 |
| 105 | A-6 | 28871 | 112 | 199 |
| 106 | A#-6 | 30588 | 119 | 124 |
| 107 | B-6 | 32407 | 126 | 151 |
| 112 | C-7 | 34334 | 134 | 30 |
| 113 | C#-7 | 36376 | 142 | 24 |
| 114 | D-7 | 38539 | 150 | 139 |
| 115 | D#-7 | 40830 | 159 | 126 |
| 116 | E-7 | 43258 | 168 | 250 |
| 117 | F-7 | 45830 | 179 | 6 |
| 118 | F#-7 | 48556 | 189 | 172 |
| 119 | G-7 | 51443 | 200 | 243 |
| 120 | G#-7 | 54502 | 212 | 230 |
| 121 | A-7 | 57743 | 225 | 143 |
| 122 | A#-7 | 61176 | 238 | 248 |
| 123 | B-7 | 64814 | 253 | 46 |
+-------------+---------------+-------------+-------------+-------------+
386 APPENDIX E
~
FILTER SETTINGS
+------------+--------------------------------+
| Location | Contents |
+------------+--------------------------------+
| 54293 | Low cutoff frequency (0-7) |
| 54294 | High cutoff frequency (0-255) |
| 54295 | Resonance (bits 4-7) |
| | Filter voice 3 (bit 2) |
| | Filter voice 2 (bit 1) |
| | Filter voice 1 (bit 0) |
| 54296 | High pass (bit 6) |
| | Bandpass (bit 5) |
| | Low pass (bit 4) |
| | Volume (bits 0-3) |
+------------+--------------------------------+
APPENDIX E 387
~
APPENDIX F
BIBLIOGRAPHY
Addison-Wesley "BASIC and the Personal Computer", Dwyer and
Critchfield
Compute "Compute's First Book of PET/CBM"
Cowbay Computing "Feed Me, I'm Your PET Computer", Carol Alexander
"Looking Good with Your PET", Carol Alexander
"Teacher's PET-Plans, Quizzes, and Answers"
Creative Computing "Getting Acquainted With Your VIC 20",
T. Hartnell
Dilithium Press "BASIC Basic-English Dictionary for the PET",
Lorry Noonan
"PET BASIC", Tom Rugg and Phil Feldman
Faulk Baker Associates "MOS Programming Manual", MOS Technology
Hoyden Book Co. "BASIC From the Ground Up", David E. Simon
"I Speak BASIC to My PET", Aubrey Jones, Jr.
"Library of PET Subroutines',', Nick Hampshire
"PET Graphics", Nick Hampshire
"BASIC Conversions Handbook, Apple, TRS-80, and
PET", David A. Brain, Phillip R. Oviatt,
Paul J. Paquin, and Chandler P. Stone
388 APPENDIX F
~
Howard W. Sams "The Howard W. Sams Crash Course in Mi-
crocomputers", Louis E. Frenzel, Jr.
"Mostly BASIC: Applications for Your PET",
Howard Berenbon
"PET Interfacing", James M. Downey and Steven
M. Rogers
"VIC 20 Programmer's Reference Guide", A. Finkel,
P. Higginbottom, N. Harris, and M. Tomczyk
Little, Brown & Co. "Computer Games for Businesses, Schools, and
Homes", J. Victor Nagigian, and William S. Hodges
"The Computer Tutor: Learning Activities for
Homes and Schools", Gary W. Orwig, University of
Central Florida, and William S. Hodges
McGraw-Hill "Hands-On BASIC With a PET", Herbert D. Peckman
"Home and Office Use of VisiCalc", D. Castlewitz,
and L. Chisauki
Osborne/McGraw-Hill "PET/CBM Personal Computer Guide", Carroll
S. Donahue
"PET Fun and Games", R. Jeffries and G. Fisher
"PET and the IEEE", A. Osborne and C. Donahue
"Some Common BASIC Programs for the PET",
L. Poole, M. Borchers, and C. Donahue
"Osborne CP/M User Guide", Thorn Hogan
"CBM Professional Computer Guide"
"The PET Personal Guide"
"The 8086 Book", Russell Rector and George Alexy
APPENDIX F 389
~
P. C. Publications "Beginning Self-Teaching Computer Lessons"
Prentice-Hall "The PET Personal Computer for Beginners",
S. Dunn and V. Morgan
Reston Publishing Co. "PET and the IEEE 488 Bus (GPIB)", Eugene
Fisher and C. W. Jensen
"PET BASIC-Training Your PET Computer",
Roman Zamora, Wm. F. Carrie, and B. Allbrecht
"PET Games and Recreation", M. Ogelsby, L.
Lindsey, and D. Kunkin
"PET BASIC", Richard Huskell
"VIC Games and Recreation"
Telmas Courseware "BASIC and the Personal Computer", T. A. Dwyer,
Ratings and M. Critchfield
Total Information Ser- "Understanding Your PET/CBM, Vol. 1, BASIC
vices Programming"
"Understanding Your VIC", David Schultz
Commodore Magazines provide you with the most up-to-date information
for your Commodore 64. Two of the most popular publications that you
should seriously consider subscribing to are:
COMMODORE-The Microcomputer Magazine is published bimonthly and is
available by subscription ($15.00 per year, U.S., and $25.00 per year,
worldwide).
POWER/PLAY-The Home Computer Magazine is, published quarterly and is
available by subscription ($10.00 per year, U.S,, and $15.00 per year
worldwide).
390 APPENDIX F
~
APPENDIX G
VIC CHIP REGISTER MAP
53248 ($D000) Starting (Base) Address
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
|Register#| | | | | | | | | |
| Dec Hex | DB7 | DB6 | DB5 | DB4 | DB3 | DB2 | DB1 | DB0 | |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 0 0 | S0X7| | | | | | | S0X0| SPRITE 0 X |
| | | | | | | | | | Component |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 1 1 | S0Y7| | | | | | | S0Y0| SPRITE 0 Y |
| | | | | | | | | | Component |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 2 2 | S1X7| | | | | | | S1X0| SPRITE 1 X |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 3 3 | S1Y7| | | | | | | S1Y0| SPRITE 1 Y |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 4 4 | S2X7| | | | | | | S2X0| SPRITE 2 X |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 5 5 | S2Y7| | | | | | | S2Y0| SPRITE 2 Y |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 6 6 | S3X7| | | | | | | S3X0| SPRITE 3 X |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 7 7 | S3Y7| | | | | | | S3Y0| SPRITE 3 Y |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 8 8 | S4X7| | | | | | | S4X0| SPRITE 4 X |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 9 9 | S4Y7| | | | | | | S4Y0| SPRITE 4 Y |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 10 A | S5X7| | | | | | | S5X0| SPRITE 5 X |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 11 B | S5Y7| | | | | | | S5Y0| SPRITE 5 Y |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 12 C | S6X7| | | | | | | S6X0| SPRITE 6 X |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 13 D | S6Y7| | | | | | | S6Y0| SPRITE 6 Y |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 14 E | S7X7| | | | | | | S7X0| SPRITE 7 X |
| | | | | | | | | | Component |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
APPENDIX G 391
~
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
|Register#| | | | | | | | | |
| Dec Hex | DB7 | DB6 | DB5 | DB4 | DB3 | DB2 | DB1 | DB0 | |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 15 F | S7Y7| | | | | | | S7Y0| SPRITE 7 Y |
| | | | | | | | | | Component |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 16 10 | S7X8| S6X8| S5X8| S4X8| S3X8| S2X8| S1X8| S0X8| MSB of X |
| | | | | | | | | | COORD. |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 17 11 | RC8 | ECM | BMM | BLNK| RSEL|YSCL2|YSCL1|YSCL0| Y SCROLL |
| | | | | | | | | | MODE |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 18 12 | RC7 | RC6 | RC5 | RC4 | RC3 | RC2 | RC1 | RC0 | RASTER |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 19 13 | LPX7| | | | | | | LPX0| LIGHT PEN X |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 20 14 | LPY7| | | | | | | | LIGHT PEN Y |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 21 15 | SE7 | | | | | | | SE0 |SPRITE ENABLE|
| | | | | | | | | | (ON/OFF) |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 22 16 | N.C.| N.C.| RST | MCM | CSEL|XSCL2|XSCL1|XSCL0| X SCROLL |
| | | | | | | | | | MODE |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 23 17 |SEXY7| | | | | | |SEXY0| SPRITE |
| | | | | | | | | | EXPAND Y |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 24 18 | VS13| VS12| VS11| VS10| CB13| CB12| CB11| N.C.| SCREEN and |
| | | | | | | | | | Character |
| | | | | | | | | | Memory Base |
| | | | | | | | | | Address |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 25 19 | IRQ | N.C.| N.C.| N.C.|LPIRQ| ISSC| ISBC| RIRQ| Interrupt |
| | | | | | | | | | Request's |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 26 1A | N.C.| N.C.| N.C.| N.C.| MLPI|MISSC|MISBC|MRIRQ| IRQ MASKS |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 27 1B | BSP7| | | | | | | BSP0| Background- |
| | | | | | | | | | Sprite |
| | | | | | | | | | PRIORITY |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
392 APPENDIX G
~
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
|Register#| | | | | | | | | |
| Dec Hex | DB7 | DB6 | DB5 | DB4 | DB3 | DB2 | DB1 | DB0 | |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 28 1C | SCM7| | | | | | | SCM0| MULTICOLOR |
| | | | | | | | | |SPRITE SELECT|
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 29 1D |SEXX7| | | | | | |SEXX0| SPRITE |
| | | | | | | | | | EXPAND X |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 30 1E | SSC7| | | | | | | SSC0|Sprite-Sprite|
| | | | | | | | | | COLLISION |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
| 31 1F | SBC7| | | | | | | SBC0| Sprite- |
| | | | | | | | | | Background |
| | | | | | | | | | COLLISION |
+---------+-----+-----+-----+-----+-----+-----+-----+-----+-------------+
+---------+-----------------------+ +---------+-----------------------+
|Register#| | |Register#| |
| Dec Hex | Color | | Dec Hex | Color |
| 32 20 | BORDER COLOR | | 39 27 | SPRITE 0 COLOR |
| 33 21 | BACKGROUND COLOR 0 | | 40 28 | SPRITE 1 COLOR |
| 34 22 | BACKGROUND COLOR 1 | | 41 29 | SPRITE 2 COLOR |
| 35 23 | BACKGROUND COLOR 2 | | 42 2A | SPRITE 3 COLOR |
| 36 24 | BACKGROUND COLOR 3 | | 43 2B | SPRITE 4 COLOR |
| 37 25 | SPRITE MULTICOLOR 0 | | 44 2C | SPRITE 5 COLOR |
| 38 26 | SPRITE MULTICOLOR 1 | | 45 2D | SPRITE 6 COLOR |
+---------+-----------------------+ | 46 2E | SPRITE 7 COLOR |
COLOR CODES +---------+-----------------------+
+---------+-----------+ +---------+-----------+
| Dec Hex | Color | | Dec Hex | Color |
| 0 0 | BLACK | | 8 8 | ORANGE |
| 1 1 | WHITE | | 9 9 | BROWN |
| 2 2 | RED | | 10 A | LT RED |
| 3 3 | CYAN | | 11 B | GRAY 1 |
| 4 4 | PURPLE | | 12 C | GRAY 2 |
| 5 5 | GREEN | | 13 D | LT GREEN |
| 6 6 | BLUE | | 14 E | LT BLUE |
| 7 7 | YELLOW | | 15 F | GRAY 3 |
+---------+-----------+ +---------+-----------+
LEGEND: ONLY COLORS 0-7 MAY BE USED IN MULTICOLOR CHARACTER MODE
APPENDIX G 393
~
APPENDIX H
DERIVING MATHEMATICAL FUNCTIONS
Functions that are not intrinsic to Commodore 64 BASIC may be calcu-
lated as follows:
+------------------------------+----------------------------------------+
| FUNCTION | BASIC EQUIVALENT |
+------------------------------+----------------------------------------+
| SECANT | SEC(X)=1/COS(X) |
| COSECANT | CSC(X)=1/SIN(X) |
| COTANGENT | COT(X)=1/TAN(X) |
| INVERSE SINE | ARCSIN(X)=ATN(X/SQR(-X*X+1)) |
| INVERSE COSINE | ARCCOS(X)=-ATN(X/SQR(-X*X+1))+{pi}/2 |
| INVERSE SECANT | ARCSEC(X)=ATN(X/SQR(X*X-1)) |
| INVERSE COSECANT | ARCCSC(X)=ATN(X/SQR(X*X-1)) |
| | +(SGN(X)-1*{pi}/2 |
| INVERSE COTANGENT | ARCOT(X)=ATN(X)+{pi}/2 |
| HYPERBOLIC SINE | SINH(X)=(EXP(X)-EXP(-X))/2 |
| HYPERBOLIC COSINE | COSH(X)=(EXP(X)+EXP(-X))/2 |
| HYPERBOLIC TANGENT | TANH(X)=EXP(-X)/(EXP(X)+EXP(-X))*2+1 |
| HYPERBOLIC SECANT | SECH(X)=2/(EXP(X)+EXP(-X)) |
| HYPERBOLIC COSECANT | CSCH(X)=2/(EXP(X)-EXP(-X)) |
| HYPERBOLIC COTANGENT | COTH(X)=EXP(-X)/(EXP(X)-EXP(-X))*2+1 |
| INVERSE HYPERBOLIC SINE | ARCSINH(X)=LOG(X+SQR(X*X+1)) |
| INVERSE HYPERBOLIC COSINE | ARCCOSH(X)=LOG(X+SQR(X*X-1)) |
| INVERSE HYPERBOLIC TANGENT | ARCTANH(X)=LOG((1+X)/(1-X))/2 |
| INVERSE HYPERBOLIC SECANT | ARCSECH(X)=LOG((SQR(-X*X+1)+1/X) |
| INVERSE HYPERBOLIC COSECANT | ARCCSCH(X)=LOG((SGN(X)*SQR(X*X+1/X) |
| INVERSE HYPERBOLIC COTANGENT| ARCCOTH(X)=LOG((X+1)/(X-1))/2 |
+------------------------------+----------------------------------------+
394 APPENDIX H
~
APPENDIX I
PINOUTS FOR INPUT/OUTPUT DEVICES
This appendix is designed to show you what connections may be made to
the Commodore 64.
1) Game I/O 4) Serial I/O (Disk/Printer)
2) Cartridge Slot 5) Modulator Output
3) Audio/Video 6) Cassette
7) User Port
Control Port 1
+-----+-------------+-----------+
| Pin | Type | Note | 1 2 3 4 5
| 1 | JOYA0 | | O O O O O
| 2 | JOYA1 | |
| 3 | JOYA2 | | O O O O
| 4 | JOYA3 | | 6 7 8 9
| 5 | POT AY | |
| 6 | BUTTON A/LP | |
| 7 | +5V | MAX. 50mA |
| 8 | GND | |
| 9 | POT AX | |
+-----+-------------+-----------+
Control Port 2
+-----+-------------+-----------+
| Pin | Type | Note |
| 1 | JOYB0 | |
| 2 | JOYB1 | |
| 3 | JOYB2 | |
| 4 | JOYB3 | |
| 5 | POT BY | |
| 6 | BUTTON B | |
| 7 | +5V | MAX. 50mA |
| 8 | GND | |
| 9 | POT BX | |
+-----+-------------+-----------+
APPENDIX I 395
~
Cartridge Expansion Slot
Pin Type Pin Type Pin Type Pin Type
+----+----------+ +----+----------+ +----+----------+ +----+----------+
| 1 | GND | | 12 | BA | | A | GND | | N | A9 |
| 2 | +5V | | 13 | /DMA | | B | /ROMH | | P | A8 |
| 3 | +5V | | 14 | D7 | | C | /RESET | | R | A7 |
| 4 | /IRQ | | 15 | D6 | | D | /NMI | | S | A6 |
| 5 | R/W | | 16 | D5 | | E | 02 | | T | A5 |
| 6 | Dot Clock| | 17 | D4 | | F | A15 | | U | A4 |
| 7 | I/O1 | | 18 | D3 | | H | A14 | | V | A3 |
| 8 | /GAME | | 19 | D2 | | J | A13 | | W | A2 |
| 9 | /EXROM | | 20 | D1 | | K | A12 | | X | A1 |
| 10 | I/O2 | | 21 | D0 | | L | A11 | | Y | A0 |
| 11 | /ROML | | 22 | GND | | M | A10 | | Z | GND |
+----+----------+ +----+----------+ +----+----------+ +----+----------+
2 2 2 1 1 1 1 1 1 1 1 1 1
2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1
+---@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@---+
| |
+---@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@-@---+
Z Y X W V U T S R P N M L K J H F E D C B A
Audio/Video Serial I/O
Pin Type Pin Type
+-------+----------------------+ +-------+----------------------+
| 1 | LUMINANCE | | 1 | /SERIAL SRQ IN |
| 2 | GND | | 2 | GND |
| 3 | AUDIO OUT | | 3 | SERIAL ATN OUT |
| 4 | VIDEO OUT | | 4 | SERIAL CLK IN/OUT |
| 5 | AUDIO IN | | 5 | SERIAL DATA IN/OUT |
| 6 | CHROMINANCE | | 6 | /RESET |
+-------+----------------------+ +-------+----------------------+
++ ++ ++ ++
/ +-+ \ / +-+ \
/ \ /5 1\
+ + + O O +
| 6 | | 6 |
|3O O O1| | O |
| | | |
+ O O + + O O +
\5 O 4/ \4 O 2/
\ 2 / \ 3 /
+---+ +---+
396 APPENDIX I
~
Cassette
+-------+--------------------+
| Pin | Type |
+-------+--------------------+
| A-1 | GND | 1 2 3 4 5 6
| B-2 | +5V | +---@-@-@-@-@-@---+
| C-3 | CASSETTE MOTOR | | |
| D-4 | CASSETTE READ | +---@-@-@-@-@-@---+
| E-5 | CASSETTE WRITE | A B C D E F
| F-6 | CASSETTE SENSE |
+-------+--------------------+
User I/O
+-----+---------------+-----------+ +-----+---------------+-----------+
| Pin | Type | Note | | Pin | Type | Note |
+-----+---------------+-----------+ +-----+---------------+-----------+
| 1 | GND | | | A | GND | |
| 2 | +5V |MAX. 100 mA| | B | /FLAG2 | |
| 3 | /RESET | | | C | PB0 | |
| 4 | CNT1 | | | D | PB1 | |
| 5 | SP1 | | | E | PB2 | |
| 6 | CNT2 | | | F | PB3 | |
| 7 | SP2 | | | H | PB4 | |
| 8 | /PC2 | | | I | PB5 | |
| 9 | SER. ATN OUT | | | K | PB6 | |
| 10 | 9 VAC |MAX. 100 mA| | L | PB7 | |
| 11 | 9 VAC |MAX. 100 mA| | M | PA2 | |
| 12 | GND | | | N | GND | |
+-----+---------------+-----------+ +-----+---------------+-----------+
1 1 1
1 2 3 4 5 6 7 8 9 0 1 2
+--@-@-@-@-@-@-@-@-@-@-@-@--+
| |
+--@-@-@-@-@-@-@-@-@-@-@-@--+
A B C D E F H J K L M N
APPENDIX I 397
~
APPENDIX J
CONVERTING STANDARD
BASIC PROGRAMS TO
COMMODORE 64 BASIC
If you have programs written in a BASIC other than Commodore BASIC,
some minor adjustments may be necessary before running them on the
Commodore-64. We've included some hints to make the conversion easier.
String Dimensions
Delete all statements that are used to declare the length of strings.
A statement such as DIM A$(I,J), which dimensions a string array for J
elements of length I, should be converted to the Commodore BASIC
statement DIM A$(J).
Some BASICs use a comma or an ampersand for string concatenation. Each
of these must be changed to a plus sign, which is the Commodore BASIC
operator for string concatenation.
In Commodore-64 BASIC, the MID$, RIGHT$, and LEFT$ functions are used
to take substrings of strings. Forms such as A$(I) to access the Ith
character in A$, or A$(I,J) to take a substring of A$ from position I to
J, must be changed as follows:
Other BASIC Commodore 64 BASIC
A$(I)=X$ A$=LEFT$(A$,I-1)+X$+MID$(A$,I+1)
A$(I,J)=X$ A$=LEFT$(A$,I-1)+X$+MID$(A$,J+1)
Multiple Assignments
To set B and C equal to zero, some BASICs allow statements of the form:
10 LET B=C=0
398 APPENDIX J
~
Commodore 64 BASIC would interpret the second equal sign as a logical
operator and set B = -1 if C = 0. Instead, convert this statement to:
10 C=0:B=0
Multiple Statements
Some BASICs use a backslash to separate multiple statements on a line.
With Commodore 64 BASIC, separate all statements by a colon (:).
MAT Functions
Programs using the MAT functions available on some BASICs must be
rewritten using FOR...NEXT loops to execute properly.
APPENDIX J 399
~
APPENDIX K
ERROR MESSAGES
This appendix contains a complete list of the error messages generated
by the Commodore-64, with a description of causes.
BAD DATA String data was received from an open file, but the
program was expecting numeric data.
BAD SUBSCRIPT The program was trying to reference an element of an
array whose number is outside of the range specified
in the DIM statement.
BREAK Program execution was stopped because you hit the
<STOP> key.
CAN'T CONTINUE The CONT command will not work, either because the
program was never RUN, there has been an error, or
a line has been edited.
DEVICE NOT PRESENT The required I/O device was not available for an
OPEN, CLOSE, CMD, PRINT#, INPUT#, or GET#.
DIVISION BY ZERO Division by zero is a mathematical oddity and not
allowed.
EXTRA IGNORED Too many items of data were typed in response to an
INPUT statement. Only the first few items were
accepted.
FILE NOT FOUND If you were looking for a file on tape, and END-OF-
TAPE marker was found. If you were looking on disk,
no file with that name exists.
FILE NOT OPEN The file specified in a CLOSE, CMD, PRINT#, INPUT#,
or GET#, must first be OPENed.
FILE OPEN An attempt was made to open a file using the number
of an already open file.
FORMULA TOO COMPLEX The string expression being evaluated should be split
into at least two parts for the system to work with,
or a formula has too many parentheses.
ILLEGAL DIRECT The INPUT statement can only be used within a pro-
gram, and not in direct mode.
ILLEGAL QUANTITY A number used as the argument of a function or
statement is out of the allowable range.
400 APPENDIX K
~
LOAD There is a problem with the program on tape.
NEXT WITHOUT FOR This is caused by either incorrectly nesting loops or
having a variable name in a NEXT statement that
doesn't correspond with one in a FOR statement.
NOT INPUT FILE An attempt was made to INPUT or GET data from a file
which was specified to be for output only.
NOT OUTPUT FILE An attempt was mode to PRINT data to a file which was
specified as input only.
OUT OF DATA A READ statement was executed but there is no data
left unREAD in a DATA statement.
OUT OF MEMORY There is no more RAM available for program or
variables. This may also occur when too many FOR
loops have been nested, or when there are too many
GOSUBs in effect.
OVERFLOW The result of a computation is larger than the
largest number allowed, which is 1.70141884E+38.
REDIM'D ARRAY An array may only be DiMensioned once. If an array
variable is used before that array is DIM'D, an
automatic DIM operation is performed on that array
setting the number of elements to ten, and any
subsequent DIMs will cause this error.
REDO FROM START Character data was typed in during an INPUT statement
when numeric data was expected. Just re-type the
entry so that it is correct, and the program will
continue by itself.
RETURN WITHOUT GOSUB A RETURN statement was encountered, and no GOSUB
command has been issued.
STRING TOO LONG A string can contain up to 255 characters.
?SYNTAX ERROR A statement is unrecognizable by the Commodore 64. A
missing or extra parenthesis, misspelled keywords,
etc.
TYPE MISMATCH This error occurs when a number is used in place of a
string, or vice-versa.
UNDEF'D FUNCTION A user defined function was referenced, but it has
never been defined using the DEF FN statement.
UNDEF'D STATEMENT An attempt was made to GOTO or GOSUB or RUN a line
number that doesn't exist.
VERIFY The program on tape or disk does not match the
program currently in memory.
APPENDIX K 401
~
APPENDIX L
6510 MICROPROCESSOR CHIP
SPECIFICATIONS
DESCRIPTION
The 6510 is a low-cost microcomputer system capable of solving a broad
range of small-systems and peripheral-control problems at minimum cost to
the user.
An 8-bit Bi-Directional I/O Port is located on-chip with the Output
Register at Address 0000 and the Data-Direction Register at Address 0001.
The I/O Port is bit-by-bit programmable.
The Three-State sixteen-bit Address Bus allows Direct Memory Accessing
(DMA) and multiprocessor systems sharing a common memory.
The internal processor architecture is identical to the MOS Technology
6502 to provide software compatibility.
FEATURES OF THE 6510...
o Eight-Bit Bi-Directional I/O Port
o Single +5-volt supply
o N-channel, silicon gate, depletion load technology
o Eight-bit parallel processing
o 56 Instructions
o Decimal and binary arithmetic
o Thirteen addressing modes
o True indexing capability
o Programmable stack pointer
o Variable length stack
o Interrupt capability
o Eight-Bit Bi-Directional Data Bus
o Addressable memory range of up to 64K bytes
o Direct memory access capability
o Bus compatible with M6800
o Pipeline architecture
o 1-MHz and 2-MHz operation
o Use with any type or speed memory
402 APPENDIX L
~
PIN CONFIGURATION
+----+ +----+
01 IN 1 @| +-+ |@ 40 /RES
| |
RDY 2 @| |@ 39 02 IN
| |
/IRQ 3 @| |@ 38 R/W
| |
/NMI 4 @| |@ 37 D0
| |
AEC 5 @| |@ 36 D1
| |
VCC 6 @| |@ 35 D2
| |
A0 7 @| |@ 34 D3
| |
A1 8 @| |@ 33 D4
| |
A2 9 @| |@ 32 D5
| |
A3 10 @| |@ 31 D6
| 6510 |
A4 11 @| |@ 30 D7
| |
A5 12 @| |@ 29 P0
| |
A6 13 @| |@ 28 P1
| |
A7 14 @| |@ 27 P2
| |
A8 15 @| |@ 26 P3
| |
A9 16 @| |@ 25 P4
| |
A10 17 @| |@ 24 P5
| |
A11 18 @| |@ 23 A15
| |
A12 19 @| |@ 22 A14
| |
A13 20 @| |@ 21 GND
+-----------+
APPENDIX L 403
~
[THE PICTURE IS MISSING!]
6510 BLOCK DIAGRAM
404 APPENDIX L
~
6510 CHARACTERISTICS
MAXIMUM RATINGS
+--------------------------+------------+-----------------+-------------+
| RATING | SYMBOL | VALUE | UNIT |
+--------------------------+------------+-----------------+-------------+
| SUPPLY VOLTAGE | Vcc | -0.3 to +7.0 | VDC |
| INPUT VOLTAGE | Vin | -0.3 to +7.0 | VDC |
| OPERATING TEMPERATURE | Ta | 0 to +70 | Celsius |
| STORAGE TEMPERATURE | Tstg | -55 to +150 | Celsius |
+--------------------------+------------+-----------------+-------------+
+-----------------------------------------------------------------------+
| NOTE: This device contains input protection against damage due to high|
| static voltages or electric fields; however, precautions should be |
| taken to avoid application of voltages higher than the maximum rating.|
+-----------------------------------------------------------------------+
ELECTRICAL CHARACTERISTICS (VCC=5.0V +-5%, VSS=0, Ta=0 to +70 Celsius)
+------------------------------------+--------+-------+---+-------+-----+
| CHARACTERISTIC | SYMBOL | MIN. |TYP| MAX. |UNIT |
+------------------------------------+--------+-------+---+-------+-----+
| Input High Voltage | | | | | |
| 01, 02(in) | Vih |Vcc-0.2| - |Vcc+1.0| VDC |
| Input High Voltage | | | | | |
| /RES, P0-P7, /IRQ, Data | |Vss+2.0| - | - | VDC |
+------------------------------------+--------+-------+---+-------+-----+
| Input Low Voltage | | | | | |
| 01,02(in) | Vil |Vss-0.3| - |Vss+0.2| VDC |
| /RES, P0-P7, /IRQ, Data | | - | - |Vss+0.8| VDC |
+------------------------------------+--------+-------+---+-------+-----+
| Input Leakage Current | | | | | |
| (Vin=0 to 5.25V, Vcc=5.25V | | | | | |
| Logic | Iin | - | - | 2.5 | uA |
| 01, 02(in) | | - | - | 100 | uA |
+------------------------------------+--------+-------+---+-------+-----+
| Three State(Off State)Input Current| | | | | |
| (Vin=0.4 to 2.4V, Vcc=5.25V) | | | | | |
| Data Lines | Itsi | - | - | 10 | uA |
+------------------------------------+--------+-------+---+-------+-----+
| Output High Voltage | | | | | |
| (Ioh=-100uADC, Vcc=4.75V) | | | | | |
| Data, A0-A15, R/W, P0-P7 | Voh |Vss+2.4| - | - | VDC |
+------------------------------------+--------+-------+---+-------+-----+
APPENDIX L 405
~
+------------------------------------+--------+-------+---+-------+-----+
| CHARACTERISTIC | SYMBOL | MIN. |TYP| MAX. |UNIT |
+------------------------------------+--------+-------+---+-------+-----+
| Out Low Voltage | | | | | |
| (Iol=1.6mADC, Vcc=4.75V) | | | | | |
| Data, A0-A15, R/W, P0-P7 | Vol | - | - |Vss+0.4| VDC |
+------------------------------------+--------+-------+---+-------+-----+
| Power Supply Current | Icc | - |125| | mA |
+------------------------------------+--------+-------+---+-------+-----+
| Capacitance | C | | | | pF |
| Vin=0, Ta=25 Celsius, f=1MHz) | | | | | |
| Logic, P0-P7 | Cin | - | - | 10 | |
| Data | | - | - | 15 | |
| A0-A15, R/W | Cout | - | - | 12 | |
| 01 | C01 | - | 30| 50 | |
| 02 | C02 | - | 50| 80 | |
+------------------------------------+--------+-------+---+-------+-----+
CLOCK TIMING
[THE PICTURE IS MISSING!]
TIMING FOR READING DATA FROM MEMORY OR PERIPHERALS
406 APPENDIX L
~
CLOCK TIMING
[THE PICTURE IS MISSING!]
TIMING FOR WRITING DATA TO MEMORY OR PERIPHERALS
APPENDIX L 407
~
AC CHARACTERISTICS
ELECTRICAL CHARACTERISTICS (Vcc=5V +-5%, Vss=0V, Ta=0-70 Celsius)
CLOCK TIMING 1 MHz TIMING 2 MHz TIMING
+---------------------------------+------+----+---+---+---+---+---+-----+
| CHARACTERISTIC |SYMBOL|MIN.|TYP|MAX|MIN|TYP|MAX|UNITS|
+---------------------------------+------+----+---+---+---+---+---+-----+
| Cycle Time | Tcyc |1000| - | - |500| - | - | ns |
+---------------------------------+------+----+---+---+---+---+---+-----+
| Clock Pulse Width 01 |PWH01 | 430| - | - |215| - | - | ns |
| (Measured at Vcc-0.2V) 02 |PWH02 | 470| - | - |235| - | - | ns |
+---------------------------------+------+----+---+---+---+---+---+-----+
| Fall Time, Rise Time | | | | | | | | |
| (Measured from 0.2V to Vcc-0.2V)|Tf, Tr| - | - | 25| - | - | 15| ns |
+---------------------------------+------+----+---+---+---+---+---+-----+
| Delay Time between Clocks | | | | | | | | |
| (Measured at 0.2V) | Td | 0 | - | - | 0 | - | - | ns |
+---------------------------------+------+----+---+---+---+---+---+-----+
READ/WRITE TIMING (LOAD=1TTL) 1 MHz TIMING 2 MHz TIMING
+---------------------------------+------+----+---+---+---+---+---+-----+
| CHARACTERISTIC |SYMBOL|MIN.|TYP|MAX|MIN|TYP|MAX|UNITS|
+---------------------------------+------+----+---+---+---+---+---+-----+
| Read/Write Setup Time from 6508 | Trws | - |100|300| - |100|150| ns |
+---------------------------------+------+----+---+---+---+---+---+-----+
| Address Setup Time from 6508 | Tads | - |100|300| - |100|150| ns |
+---------------------------------+------+----+---+---+---+---+---+-----+
| Memory Read Access Time | Tacc | - | - |575| - | - |300| ns |
+---------------------------------+------+----+---+---+---+---+---+-----+
| Data Stability Time Period | Tdsu | 100| - | - | 50| | | ns |
+---------------------------------+------+----+---+---+---+---+---+-----+
| Data Hold Time-Read | Thr | | - | - | | | | ns |
+---------------------------------+------+----+---+---+---+---+---+-----+
| Data Hold Time-Write | Thw | 10| 30| - | 10| 30| | ns |
+---------------------------------+------+----+---+---+---+---+---+-----+
| Data Setup Time from 6510 | Tmds | - |150|200| - | 75|100| ns |
+---------------------------------+------+----+---+---+---+---+---+-----+
| Address Hold Time | Tha | 10| 30| - | 10| 30| | ns |
+---------------------------------+------+----+---+---+---+---+---+-----+
| R/W Hold Time | Thrw | 10| 30| - | 10| 30| | ns |
+---------------------------------+------+----+---+---+---+---+---+-----+
408 APPENDIX L
~
+---------------------------------+------+----+---+---+---+---+---+-----+
| Delay Time, Address valid to | | | | | | | | |
| 02 positive transition | Taew | 180| - | - | | | | ns |
+---------------------------------+------+----+---+---+---+---+---+-----+
| Delay Time, 02 positive | | | | | | | | |
| transition to Data valid on bus | Tedr | - | - |395| | | | ns |
+---------------------------------+------+----+---+---+---+---+---+-----+
| Delay Time, data valid to 02 | | | | | | | | |
| negative transition | Tdsu | 300| - | - | | | | ns |
+---------------------------------+------+----+---+---+---+---+---+-----+
| Delay Time, R/W negative | | | | | | | | |
| transition to 02 positive trans.| Twe | 130| - | - | | | | ns |
+---------------------------------+------+----+---+---+---+---+---+-----+
| Delay Time, 02 negative trans. | | | | | | | | |
| to Peripheral data valid | Tpdw | - | - | 1 | | | | us |
+---------------------------------+------+----+---+---+---+---+---+-----+
| Peripheral Data Setup Time | Tpdsu| 300| - | - | | | | ns |
+---------------------------------+------+----+---+---+---+---+---+-----+
| Address Enable Setup Time | Taes | | | 60| | | 60| ns |
+---------------------------------+------+----+---+---+---+---+---+-----+
APPENDIX L 409
~
SIGNAL DESCRIPTION
Clocks (01, 02)
The 6510 requires a two-phase non-overlapping clock that runs at the
Vcc voltage level.
Address Bus (A0-A15)
These outputs are TTL compatible, capable of driving one standard TTL
load and 130 pf.
Data Bus (D0-D7)
Eight pins are used for the data bus. This is a Bi-Directional bus,
transferring data to and from the device and peripherals. The outputs are
tri-state buffers capable of driving one standard TTL load and 130 pf.
Reset
This input is used to reset or start the microprocessor from a power
down condition. During the time that this line is held low, writing to or
from the microprocessor is inhibited. When a positive edge is detected on
the input, the microprocessor will immediately begin the reset sequence.
After a system initialization time of six clock cycles, the mask
interrupt flag will be set and the microprocessor will load the program
counter from the memory vector locations FFFC and FFFD. This is the start
location for program control.
After Vcc reaches 4.75 volts in a power-up routine, reset must be held
low for at least two clock cycles. At this time the R/W signal will
become valid.
When the reset signal goes high following these two clock cycles, the
microprocessor will proceed with the normal reset procedure detailed
above.
Interrupt Request (/IRQ)
This TTL level input requests that an interrupt sequence begin within
the microprocessor. The microprocessor will complete the current in-
struction being executed before recognizing the request. At that time,
the interrupt mask bit in the Status Code Register will be examined. If
the interrupt mask flag is not set, the microprocessor will begin an
410 APPENDIX L
~
interrupt sequence. The Program Counter and Processor Status Register are
stored in the stack. The microprocessor will then set the interrupt mask
flag high so that no further interrupts may occur. At the end of this
cycle, the program counter low will be loaded from address FFFE, and
program counter high from location FFFF, therefore transferring program
control to the memory vector located at these addresses.
Address Enable Control (AEC)
The Address Bus is valid only when the Address Enable Control line is
high. When low, the Address Bus is in a high-impedance state. This
feature allows easy DMA and multiprocessor systems.
I/O Port (P0-P7)
Six pins are used for the peripheral port, which can transfer data to
or from peripheral devices. The Output Register is located in RAM at
address 0001, and the Data Direction Register is at Address 0000. The
outputs are capable at driving one standard TTL load and 130 pf.
Read/Write (R/W)
This signal is generated by the microprocessor to control the direction
of data transfers on the Data Bus. This line is high except when the
microprocessor is writing to memory or a peripheral device.
ADDRESSING MODES
ACCUMULATOR ADDRESSING - This form of addressing is represented with a
one byte instruction, implying an operation on the accumulator.
IMMEDIATE ADDRESSING - In immediate addressing, the operand is contained
in the second byte of the instruction, with no further memory addressing
required.
ABSOLUTE ADDRESSING - In absolute addressing, the second byte of the
instruction specifies the eight low order bits of the effective address
while the third byte specifies the eight high order bits. Thus, the
absolute addressing mode allows access to the entire 64K bytes of
addressable memory.
ZERO PAGE ADDRESSING - The zero page instructions allow for shorter code
APPENDIX L 411
~
and execution times by only fetching the second byte of the instruction
and assuming a zero high address byte. Careful use of the zero page can
result in significant increase in code efficiency.
INDEXED ZERO PAGE ADDRESSING - (X, Y indexing)-This form of addressing is
used in conjunction with the index register and is referred to as "Zero
Page, X" or "Zero Page, Y." The effective address is calculated by adding
the second byte to the contents of the index register. Since this is a
form of "Zero Page" addressing, the content of the second byte references
a location in page zero. Additionally, due to the "Zero Page" addressing
nature of this mode, no carry is added to the high order 8 bits of memory
and crossing of page boundaries does not occur.
INDEXED ABSOLUTE ADDRESSING - (X, Y indexing)-This form of addressing is
used in conjunction with X and Y index register and is referred to as
"Absolute, X," and "Absolute, Y." The effective address is formed by
adding the contents of X and Y to the address contained in the second and
third bytes of the instruction. This mode allows the index register to
contain the index or count value and the instruction to contain the base
address. This type of indexing allows any location referencing and the
index to modify multiple fields resulting in reduced coding and execution
time.
IMPLIED ADDRESSING - In the implied addressing mode, the address
containing the operand is implicitly stated in the operation code of the
instruction.
RELATIVE ADDRESSING - Relative addressing is used only with branch
instructions and establishes a destination for the conditional branch.
The second byte of the instruction becomes the operand which is an
"Offset" added to the contents of the lower eight bits of the program
counter when the counter is set at the next instruction. The range of the
offset is -128 to +127 bytes from the next instruction.
INDEXED INDIRECT ADDRESSING - In indexed indirect addressing (referred to
as [Indirect, X]), the second byte of the instruction is added to the
contents of the X index register, discarding the carry. The result of
this addition points to a memory location on page zero whose contents is
the low order eight bits of the effective address. The next memory loca-
tion in page zero contains the high order eight bits of the effective ad-
dress. Both memory locations specifying the high and low order bytes of
412 APPENDIX L
~
the effective address must be in page zero.
INDIRECT INDEXED ADDRESSING - In indirect indexed addressing (referred to
as [Indirect], Y), the second byte of the instruction points to a memory
location in page zero. The contents of this memory location is added to
the contents of the Y index register, the result being the low order
eight bits of the effective address. The carry from this addition is
added to the contents of the next page zero memory location, the result
being the high order eight bits of the effective address.
ABSOLUTE INDIRECT - The second byte of the instruction contains the low
order eight bits of a memory location. The high order eight bits of that
memory location is contained in the third byte of the instruction. The
contents of the fully specified memory location is the low order byte of
the effective address. The next memory location contains the high order
byte of the effective address which is loaded into the sixteen bits of
the program counter.
INSTRUCTION SET - ALPHABETIC SEQUENCE
ADC Add Memory to Accumulator with Carry
AND "AND" Memory with Accumulator
ASL Shift left One Bit (Memory or Accumulator)
BCC Branch on Carry Clear
BCS Branch on Carry Set
BEQ Branch on Result Zero
BIT Test Bits in Memory with Accumulator
BMI Branch on Result Minus
BNE Branch on Result not Zero
BPL Branch on Result Plus
BRK Force Break
BVC Branch on Overflow Clear
BVS Branch on Overflow Set
CLC Clear Carry Flag
CLD Clear Decimal Mode
CLI Clear Interrupt Disable Bit
CLV Clear Overflow Flag
CMP Compare Memory and Accumulator
CPX Compare Memory and Index X
CPY Compare Memory and Index Y
APPENDIX L 413
~
DEC Decrement Memory by One
DEX Decrement Index X by One
DEY Decrement Index Y by One
EOR "Exclusive-OR" Memory with Accumulator
INC Increment Memory by One
INX Increment Index X by one
INY Increment Index Y by one
JMP Jump to New location
JSR Jump to New Location Saving Return Address
LDA Load Accumulator with Memory
LDX Load Index X with Memory
LDY Load Index Y with Memory
LSR Shift One Bit Right (Memory or Accumulator)
NOP No Operation
ORA "OR" Memory with Accumulator
PHA Push Accumulator on Stack
PHP Push Processor Status on Stack
PLA Pull Accumulator from Stack
PLP Pull Processor Status from Stack
ROL Rotate One Bit Left (Memory or Accumulator)
ROR Rotate One Bit Right (Memory or Accumulator)
RTI Return from Interrupt
RTS Return from Subroutine
SBC Subtract Memory from Accumulator with Borrow
SEC Set Carry Flag
SED Set Decimal Mode
SEI Set Interrupt Disable Status
STA Store Accumulator in Memory
STX Store Index X in Memory
STY Store Index Y in Merrory
414 APPENDIX L
~
TAX Transfer Accumulator to Index X
TAY Transfer Accumulator to Index Y
TSX Transfer Stack Pointer to Index X
TXA Transfer Index X to Accumulator
TXS Transfer Index X to Stack Register
TYA Transfer Index Y to Accumulator
PROGRAMMING MODEL
+---------------+
| A | ACCUMULATOR A
+---------------+
+---------------+
| Y | INDEX REGISTER Y
+---------------+
+---------------+
| X | INDEX REGISTER X
+---------------+
15 7 0
+---------------+---------------+
| PCH | PCL | PROGRAM COUNTER "PC"
+---------------+---------------+
8 7 0
+-+---------------+
|1| S | STACK POINTER "S"
+-+---------------+
7 0
+-+-+-+-+-+-+-+-+
|N|V| |B|D|I|Z|C| PROCESSOR STATUS REG "P"
+-+-+-+-+-+-+-+-+
| | | | | | |
| | | | | | +> CARRY 1=TRUE
| | | | | +--> ZERO 1=RESULT ZERO
| | | | +----> IRQ DISABLE 1=DISABLE
| | | +------> DECIMAL MODE 1=TRUE
| | +--------> BRK COMMAND
| |
| +------------> OVERFLOW 1=TRUE
+--------------> NEGATIVE 1=NEG
APPENDIX L 415
~
INSTRUCTION SET - OP CODES, EXECUTION TIME, MEMORY REQUIREMENTS
[THE PICTURE IS MISSING!]
+-----------------------------------------------------------------------+
| NOTE: COMMODORE SEMICONDUCTOR GROUP cannot assume liability for the |
| use of undefined OP CODES. |
+-----------------------------------------------------------------------+
416 APPENDIX L
~
INSTRUCTION SET - OP CODES, EXECUTION TIME, MEMORY REQUIREMENTS
[THE PICTURE IS MISSING!]
APPENDIX L 417
~
6510 MEMORY MAP
+-------------------+
FFFF | |
| ADDRESSABLE |
/ EXTERNAL /
/ MEMORY /
| |
0200 | |
+-------------------+ STACK
01FF | | STACK | | 01FF <--- POINTER
0100 | \|/ Page 1 \|/ | INITIALIZED
+-------------------+
00FF | |
| Page 0 |
+-------------------+
| OUTPUT REGISTER | 0001 <-+- Used For
+-------------------+ | Internal
0000 |DATA DIRECTION REG.| 0000 <-+ I/O Port
+-------------------+
APPLICATIONS NOTES
Locating the Output Register at the internal I/O Port in Page Zero
enhances the powerful Zero Page Addressing instructions of the 6510.
By assigning the I/O Pins as inputs (using the Data Direction Register)
the user has the ability to change the contents of address 0001 (the
Output Register) using peripheral devices. The ability to change these
contents using peripheral inputs, together with Zero Page Indirect
Addressing instructions, allows novel and versatile programming tech-
niques not possible earlier.
+-----------------------------------------------------------------------+
| COMMODORE SEMICONDUCTOR GROUP reserves the right to make changes to |
| any products herein to improve reliability, function or design. |
| COMMODORE SEMICONDUCTOR GROUP does not assume any liability arising |
| out of the application or use of any product or circuit described |
| herein; neither does it convey any license under its patent rights nor|
| the rights of others. |
+-----------------------------------------------------------------------+
418 APPENDIX L
~
APPENDIX M
6526 COMPLEX INTERFACE ADAPTER
(CIA) CHIP SPECIFICATIONS
DESCRIPTION
The 6526 Complex Interface Adapter (CIA) is a 65XX bus compatible
peripheral interface device with extremely flexible timing and I/O
capabilities.
FEATURES
o 16 Individually programmable 110 lines
o 8 or 16-Bit handshaking on read or write
o 2 independent, linkable 16-Bit interval timers
o 24-hour (AM/PM) time of day clock with programmable alarm
o 8-Bit shift register for serial I/O
o 2 TTL load capability
o CMOS compatible I/O lines
o 1 or 2 MHz operation available
APPENDIX M 419
~
PIN CONFIGURATION
+----+ +----+
Vss 1 @| +-+ |@ 40 CNT
| |
PA0 2 @| |@ 39 SP
| |
PA1 3 @| |@ 38 RS0
| |
PA2 4 @| |@ 37 RS1
| |
PA3 5 @| |@ 36 RS2
| |
PA4 6 @| |@ 35 RS3
| |
PA5 7 @| |@ 34 /RES
| |
PA6 8 @| |@ 33 D0
| |
PA7 9 @| |@ 32 D1
| |
PB0 10 @| |@ 31 D2
| 6526 |
PB1 11 @| |@ 30 D3
| |
PB2 12 @| |@ 29 D4
| |
PB3 13 @| |@ 28 D5
| |
PB4 14 @| |@ 27 D6
| |
PB5 15 @| |@ 26 D7
| |
PB6 16 @| |@ 25 02
| |
PB7 17 @| |@ 24 /FLAG
| |
/PC 18 @| |@ 23 /CS
| |
TOD 19 @| |@ 22 R/W
| |
Vcc 20 @| |@ 21 /IRQ
+-----------+
420 APPENDIX M
~
6526 BLOCK DIAGRAM
[THE PICTURE IS MISSING!]
APPENDIX M 421
~
MAXIMUM RATINGS
Supply Voltage, Vcc -0.3V to +7.0V
Input/Output Voltage, Vin -0.3V to +7.0V
Operating Temperature, Top 0 to 70 Celsius
Storage Temperature, Tstg -55 to 150 Celsius
All inputs contain protection circuitry to prevent damage due to high
static discharges. Care should be exercised to prevent unnecessary ap-
plication of voltages in excess of the allowable limits.
COMMENT
Stresses above those listed under "Absolute Maximum Ratings" may cause
permanent damage to the device. These are stress ratings oily. Functional
operation of this device at these or any other conditions above those
indicated in the operational sections of this specification is not
implied and exposure to absolute maximum rating conditions for extended
periods may affect device reliability.
ELECTRICAL CHARACTERISTICS (Vcc +-5%, Vss=0V, Ta=0-70 Celsius)
+-------------------------------+--------+-------+-------+-------+------+
| CHARACTERISTIC | SYMBOL | MIN. | TYP. | MAX. | UNIT |
+-------------------------------+--------+-------+-------+-------+------+
| Input High Voltage | Vih | +2.4 | - | Vcc | V |
+-------------------------------+--------+-------+-------+-------+------+
| Input Low Voltage | Vil | -0.3 | - | - | V |
+-------------------------------+--------+-------+-------+-------+------+
| Input Leakage Current; | Iin | - | 1.0 | 2.5 | uA |
| Vin=Vss+5V | | | | | |
| (TOD, R/W, /FLAG, 02, | | | | | |
| /RES, RS0-RS3, /CS) | | | | | |
+-------------------------------+--------+-------+-------+-------+------+
422 APPENDIX M
~
+-------------------------------+--------+-------+-------+-------+------+
| CHARACTERISTIC | SYMBOL | MIN. | TYP. | MAX. | UNIT |
+-------------------------------+--------+-------+-------+-------+------+
| Port Input Pull-up Resistance | Rpi | 3.1 | 5.0 | - | kohms|
+-------------------------------+--------+-------+-------+-------+------+
| Output Leakage Current for | Itsi | - |+-1.0 |+-10.0 | uA |
| High Impedance State (Three | | | | | |
| State); Vin=4V to 2.4V; | | | | | |
| (D0-D7, SP, CNT, /IRQ) | | | | | |
+-------------------------------+--------+-------+-------+-------+------+
| Output High Voltage | Voh | +2.4 | - | Vcc | V |
| Vcc=MIN, Iload < | | | | | |
| -200uA (PA0-PA7, /PC, | | | | | |
| PB0-PB7, D0-D7) | | | | | |
+-------------------------------+--------+-------+-------+-------+------+
| Output Low Voltage | Vol | - | - | +0.40 | V |
| Vcc=MIN, Iload < 3.2 mA | | | | | |
+-------------------------------+--------+-------+-------+-------+------+
| Output High Current (Sourcing)| Ioh | -200 | -1000 | - | uA |
| Voh > 2.4V (PA0-PA7, | | | | | |
| PB0-PB7, /PC, D0-D7 | | | | | |
+-------------------------------+--------+-------+-------+-------+------+
| Output Low Current (Sinking); | Iol | 3.2 | - | - | mA |
| Vol < .4V (PA0-PA7, /PC, | | | | | |
| PB0-PB7, D0-D7 | | | | | |
+-------------------------------+--------+-------+-------+-------+------+
| Input Capacitance | Cin | - | 7 | 10 | pf |
+-------------------------------+--------+-------+-------+-------+------+
| Output Capacitance | Cout | - | 7 | 10 | pf |
+-------------------------------+--------+-------+-------+-------+------+
| Power Supply Current | Icc | - | 70 | 100 | mA |
+-------------------------------+--------+-------+-------+-------+------+
APPENDIX M 423
~
6526 WRITE TIMING DIAGRAM
[THE PICTURE IS MISSING!]
424 APPENDIX M
~
6526 READ TIMING DIAGRAM
[THE PICTURE IS MISSING!]
APPENDIX M 425
~
6526 INTERFACE SIGNALS
02-Clock Input
The 02 clock is a TTL compatible input used for internal device opera-
tion and as a timing reference for communicating with the system data
bus.
/CS-Chip Select Input
The /CS input controls the activity of the 6526. A low level on /CS
while 02 is high causes the device to respond to signals on the R/W and
address (RS) lines. A high on /CS prevents these lines from controlling
the 6526. The /CS line is normally activated (low) at 02 by the
appropriate address combination.
R/W-Read/Write Input
The R/W signal is normally supplied by the microprocessor and controls
the direction of data transfers of the 6526. A high on R/W indicates
a read (data transfer out of the 6526), while a low indicates a write
(data transfer into the 6526).
RS3-RS0-Address Inputs
The address inputs select the internal registers as described by the
Register Map.
DB7-DB0-Data Bus Inputs/Outputs
The eight data bus pins transfer information between the 6526 and the
system data bus. These pins are high impedance inputs unless CS is low
and R/W and 02 are high to read the device. During this read, the data
bus output buffers are enabled, driving the data from the selected
register onto the system data bus.
IRQ-Interrupt Request Output
IRQ is an open drain output normally connected to the processor inter-
rupt input. An external pullup resistor holds the signal high, allowing
multiple IRQ outputs to be connected together. The IRQ output is normally
426 APPENDIX M
~
off (high impedance) and is activated low as indicated in the functional
description.
/RES-Reset Input
A low on the RES pin resets all internal registers. The port pins are
set as inputs and port registers to zero (although a read of the ports
will return all highs because of passive pullups). The timer control
registers are set to zero and the timer latches to all ones. All other
registers are reset to zero.
6526 TIMING CHARACTERISTICS
+--------+-----------------------+---------------+---------------+------+
| | | 1MHz | 2MHz | |
| | +-------+-------+-------+-------+ |
| Symbol | Characteristic | MIN | MAX | MIN | MAX | Unit |
+--------+-----------------------+-------+-------+-------+-------+------+
| | 02 CLOCK | | | | | |
| Tcyc | Cycle Time | 1000 |20,000 | 500 |20,000 | ns |
| Tr, Tf | Rise and Fall Time | - | 25 | - | 25 | ns |
| Tchw | Clock Pulse Width | | | | | |
| | (High) | 420 |10,000 | 200 |10,000 | ns |
| Tclw | Clock Pulse Width | | | | | |
| | (Low) | 420 |10,000 | 200 |10,000 | ns |
+--------+-----------------------+-------+-------+-------+-------+------+
| | WRITE CYCLE | | | | | |
| Tpd | Output Delay From 02 | - | 1000 | - | 500 | ns |
| Twcs | /CS low while 02 high | 420 | - | 200 | - | ns |
| Tads | Address Setup Time | 0 | - | 0 | - | ns |
| Tadh | Address Hold Time | 10 | - | 5 | - | ns |
| Trws | R/W Setup Time | 0 | - | 0 | - | ns |
| Trwh | R/W Hold Time | 0 | - | 0 | - | ns |
| Tds | Data Bus Setup Time | 150 | - | 75 | - | ns |
| Tdh | Data Bus Hold Time | 0 | - | 0 | - | ns |
+--------+-----------------------+-------+-------+-------+-------+------+
| | READ CYCLE | | | | | |
| Tps | Port Setup Time | 300 | - | 150 | - | ns |
| Twcs(2)| /CS low while 02 high | 420 | - | 20 | - | ns |
| Tads | Address Setup Time | 0 | - | 0 | - | ns |
| Tadh | Address Hold Time | 10 | - | 5 | - | ns |
| Trws | R/W Setup Time | 0 | - | 0 | - | ns |
| Trwh | R/W Hold Time | 0 | - | 0 | - | ns |
APPENDIX M 427
~
+--------+-----------------------+---------------+---------------+------+
| | | 1MHz | 2MHz | |
| | +-------+-------+-------+-------+ |
| Symbol | Characteristic | MIN | MAX | MIN | MAX | Unit |
+--------+-----------------------+-------+-------+-------+-------+------+
| Tacc | Data Access from | | | | | |
| | RS3-RS0 | - | 550 | - | 275 | ns |
| Tco(3) | Data Access from /CS | - | 320 | - | 150 | ns |
| Tdr | Data Release Time | 50 | - | 25 | - | ns |
+--------+-----------------------+-------+-------+-------+-------+------+
+-----------------------------------------------------------------------+
| NOTES: 1 -All timings are referenced from Vil max and Vih min on |
| inputs and Vol max and Voh min on outputs. |
| 2 -Twcs is measured from the later of 02 high or /CS low. /CS |
| must be low at least until the end of 02 high. |
| 3 -Tco is measured from the later of 02 high or /CS low. |
| Valid data is available only after the later of Tacc or Tco. |
+-----------------------------------------------------------------------+
REGISTER MAP
+---+---+---+---+---+----------+----------------------------------------+
|RS3|RS2|RS1|RS0|REG| NAME | |
+---+---+---+---+---+----------+----------------------------------------+
| 0 | 0 | 0 | 0 | 0 | PRA | PERIPHERAL DATA REG A |
| 0 | 0 | 0 | 1 | 1 | PRB | PERIPHERAL DATA REG B |
| 0 | 0 | 1 | 0 | 2 | DDRA | DATA DIRECTION REG A |
| 0 | 0 | 1 | 1 | 3 | DDRB | DATA DIRECTION REG B |
| 0 | 1 | 0 | 0 | 4 | TA LO | TIMER A LOW REGISTER |
| 0 | 1 | 0 | 1 | 5 | TA HI | TIMER A HIGH REGISTER |
| 0 | 1 | 1 | 0 | 6 | TB LO | TIMER B LOW REGISTER |
| 0 | 1 | 1 | 1 | 7 | TB HI | TIMER B HIGH REGISTER |
| 1 | 0 | 0 | 0 | 8 | TOD 10THS| 10THS OF SECONDS REGISTER |
| 1 | 0 | 0 | 1 | 9 | TOD SEC | SECONDS REGISTER |
| 1 | 0 | 1 | 0 | A | TOD MIN | MINUTES REGISTER |
| 1 | 0 | 1 | 1 | B | TOD HR | HOURS-AM/PM REGISTER |
| 1 | 1 | 0 | 0 | C | SDR | SERIAL DATA REGISTER |
| 1 | 1 | 0 | 1 | 0 | ICR | INTERRUPT CONTROL REGISTER |
| 1 | 1 | 1 | 0 | E | CRA | CONTROL REG A |
| 1 | 1 | 1 | 1 | F | CRB | CONTROL REG B |
+---+---+---+---+---+----------+----------------------------------------+
428 APPENDIX M
~
6526 FUNCTIONAL DESCRIPTION
I/O Ports (PRA, PRB, DDRA, DDRB).
Ports A and B each consist of an 8-bit Peripheral Data Register (PR)
and an 8-bit Data Direction Register (DDR). If a bit in the DDR is set to
a one, the corresponding bit in the PR is an output; if a DDR bit is set
to a zero, the corresponding PR bit is defined as an input. On a READ,
the PR reflects the information present on the actual port pins (PA0-PA7,
PB0-PB7) for both input and output bits. Port A and Port B have passive
pull-up devices as well as active pull-ups, providing both CMOS and TTL
compatibility. Both ports have two TTL load drive capability. In addition
to normal I/O operation, PB6 and PB7 also provide timer output functions.
Handshaking
Handshaking on data transfers can be accomplished using the /PC output
pin and the FLAG input pin. PC will go low for one cycle following a read
or write of PORT B. This signal can be used to indicate "data ready" at
PORT B or "data accepted" from PORT B. Handshaking on 16-bit data
transfers (using both PORT A and PORT B) is possible by always reading or
writing PORT A first. /FLAG is a negative edge sensitive input which can
be used for receiving the /PC output from another 6526, or as a general
purpose interrupt input. Any negative transition of /FLAG will set the
/FLAG interrupt bit.
+-----+---------+------+------+------+------+------+------+------+------+
| REG | NAME | D7 | D6 | D5 | D4 | D3 | D2 | D1 | D0 |
+-----+---------+------+------+------+------+------+------+------+------+
| 0 | PRA | PA7 | PA6 | PA5 | PA4 | PA3 | PA2 | PA1 | PA0 |
| 1 | PRB | PB7 | PB6 | PB5 | PB4 | PB3 | PB2 | PB1 | PB0 |
| 2 | DDRA | DPA7 | DPA6 | DPA5 | DPA4 | DPA3 | DPA2 | DPA1 | DPA0 |
| 3 | DDRB | DPB7 | DPB6 | DPB5 | DPB4 | DPB3 | DPB2 | DPB1 | DPB0 |
+-----+---------+------+------+------+------+------+------+------+------+
Interval Timers (Timer A, Timer B)
Each interval timer consists of a 16-bit read-only Timer Counter and a
16-bit write-only Timer Latch. Data written to the timer are latched in
the Timer Latch, while data read from the timer are the present contents
of the Time Counter. The timers can be used independently or linked for
extended operations. The various timer modes allow generation of long
time delays, variable width pulses, pulse trains and variable frequency
APPENDIX M 429
~
waveforms. Utilizing the CNT input, the timers can count external pulses
or measure frequency, pulse width and delay times of external signals.
Each timer has an associated control register, providing independent
control of the following functions:
Start/Stop
A control bit allows the timer to be started or stopped by the micro-
processor at any time.
PB On/Off:
A control bit allows the timer output to appear on a PORT B output line
(PB6 for TIMER A and PB7 for TIMER B). This function overrides the DDRB
control bit and forces the appropriate PB line to an output.
Toggle/Pulse
A control bit selects the output applied to PORT B. On every timer
underflow the output can either toggle or generate a single positive
pulse of one cycle duration. The Toggle output is set high whenever the
timer is started and is set low by /RES.
One-Shot/Continuous
A control bit selects either timer mode. In one-shot mode, the timer
will count down from the latched value to zero, generate an interrupt,
reload the latched value, then stop. In continuous mode, the timer will
count from the latched value to zero, generate' an interrupt, reload the
latched value and repeat the procedure continuously.
Force Load
A strobe bit allows the timer latch to be loaded into the timer counter
at any time, whether the timer is running or not.
Input Mode:
Control bits allow selection of the clock used to decrement the timer.
TIMER A can count 02 clock pulses or external pulses applied to the CNT
pin. TIMER B can count (02 pulses, external CNT pulses, TIMER A underflow
pulses or TIMER A underflow pulses while the CNT pin is held high.
430 APPENDIX M
~
The timer latch is loaded into the timer on any timer underflow, on a
force load or following a write to the high byte of the prescaler while
the timer is stopped. If the timer is running, a write to the high byte
will load the timer latch, but not reload the counter.
READ (TIMER)
REG NAME
+-----+---------+------+------+------+------+------+------+------+------+
| 4 | TA LO | TAL7 | TAL6 | TAL5 | TAL4 | TAL3 | TAL2 | TAL1 | TAL0 |
| 5 | TA HI | TAH7 | TAH6 | TAH5 | TAH4 | TAH3 | TAH2 | TAH1 | TAH0 |
| 6 | TB LO | TBL7 | TBL6 | TBL5 | TBL4 | TBL3 | TBL2 | TBL1 | TBL0 |
| 7 | TB HI | TBH7 | TBH6 | TBH5 | TBH4 | TBH3 | TBH2 | TBH1 | TBH0 |
+-----+---------+------+------+------+------+------+------+------+------+
WRITE (PRESCALER)
REG NAME
+-----+---------+------+------+------+------+------+------+------+------+
| 4 | TA LO | PAL7 | PAL6 | PAL5 | PAL4 | PAL3 | PAL2 | PAL1 | PAL0 |
| 5 | TA HI | PAH7 | PAH6 | PAH5 | PAH4 | PAH3 | PAH2 | PAH1 | PAH0 |
| 6 | TB LO | PBL7 | PBL6 | PBL5 | PBL4 | PBL3 | PBL2 | PBL1 | PBL0 |
| 7 | TB HI | PBH7 | PBH6 | PBH5 | PBH4 | PBH3 | PBH2 | PBH1 | PBH0 |
+-----+---------+------+------+------+------+------+------+------+------+
Time of Day Clock (TOD)
The TOD clock is a special purpose timer for real-time applications.
TOD consists of a 24-hour (AM/PM) clock with 1/10th second resolution. It
is organized into 4 registers: 10ths of seconds, Seconds, Minutes and
Hours. The AM/PM flag is in the MSB of the Hours register for easy bit
testing. Each register reads out in BCD format to simplify conversion for
driving displays, etc. The clock requires an external 60 Hz or 50 Hz
(programmable) TTL level input on the TOD pin for accurate time-keeping.
In addition to time-keeping, a programmable ALARM is provided for
generating an interrupt at a desired time. The ALARM registers or located
at the same addresses as the corresponding TOD registers. Access to the
ALARM is governed by a Control Register bit. The ALARM is write-only; any
read of a TOD address will read time regardless of the state of the ALARM
access bit.
A specific sequence of events must be followed for proper setting and
reading of TOD. TOD is automatically stopped whenever a write to the
Hours register occurs. The clock will not start again until after a write
to the 10ths of seconds register. This assures TOD will always start at
the desired time. Since a carry from one stage to the next can occur at
APPENDIX M 431
~
any time with respect to a read operation, a latching function is
included to keep all Time Of Day information constant during a read
sequence. All four TOD registers latch on a read of Hours and remain
latched until after a read of 10ths of seconds. The TOD clock continues
to count when the output registers are latched. If only one register is
to be read, there is no carry problem and the register can be read "on
the fly," provided that any read of Hours is followed by a read of 10ths
of seconds to disable the latching.
READ
REG NAME
+-----+---------+------+------+------+------+------+------+------+------+
| 8 |TOD 10THS| 0 | 0 | 0 | 0 | T8 | T4 | T2 | T1 |
| 9 |TOD SEC | 0 | SH4 | SH2 | SH1 | SL8 | SL4 | SL2 | SL1 |
| A |TOD MIN | 0 | MH4 | MH2 | MH1 | ML8 | ML4 | ML2 | ML1 |
| B |TOD HR | PM | 0 | 0 | HH | HL8 | HL4 | HL2 | HL1 |
+-----+---------+------+------+------+------+------+------+------+------+
WRITE
CRB7=0 TOD
CRB7=1 ALARM
(SAME FORMAT AS READ)
Serial Port (SDR)
The serial port is a buffered, 8-bit synchronous shift register system.
A control bit selects input or output mode. In input mode, data on the SP
pin is shifted into the shift register on the rising edge of the signal
applied to the CNT pin. After 8 CNT pulses, the data in the shift
register is dumped into the Serial Data Register and an interrupt is
generated. In the output mode, TIMER A is used for the baud rate
generator. Data is shifted out on the SP pin at 1/2 the underflow rate of
TIMER A. The maximum baud rate possible is 02 divided by 4, but the
maximum useable baud rate will be determined by line loading and the
speed at which the receiver responds to input data. Transmission will
start following a write to the Serial Data Register (provided TIMER A is
running and in continuous mode). The clock signal derived from TIMER A
appears as an output on the CNT pin. The data in the Serial Data Register
will be loaded into the shift register then shift out to the SP pin when
a CNT pulse occurs. Data shifted out becomes valid on the falling edge of
CNT and remains valid until the next falling edge. After 8 CNT pulses, an
432 APPENDIX M
~
interrupt is generated to indicate more data can be sent. If the Serial
Data Register was loaded with new information prior to this interrupt,
the new data will automatically be loaded into the shift register and
transmission will continue. If the microprocessor stays one byte ahead of
the shift register, transmission will be continuous. If no further data
is to be transmitted, after the 8th CNT pulse, CNT will return high and
SP will remain at the level of the last data bit transmitted. SDR data is
shifted out MSB first and serial input data should also appear in this
format.
The bidirectional capability of the Serial Port and CNT clock allows
many 6526 devices to be connected to a common serial communication bus on
which one 6526 acts as a master, sourcing data and shift clock, while all
other 6526 chips act as slaves. Both CNT and SP outputs are open drain to
allow such a common bus. Protocol for master/slave selection can be
transmitted over the serial bus, or via dedicated handshaking lines.
REG NAME
+-----+---------+------+------+------+------+------+------+------+------+
| C | SDR | S7 | S6 | S5 | S4 | S3 | S2 | S1 | S0 |
+-----+---------+------+------+------+------+------+------+------+------+
Interrupt Control (ICR)
There are five sources of interrupts on the 6526: underflow from TIMER
A, underflow from TIMER B, TOD ALARM, Serial Port full/empty and /FLAG.
A single register provides masking and interrupt information. The
interrupt Control Register consists of a write-only MASK register and a
read-only DATA register. Any interrupt will set the corresponding bit in
the DATA register. Any interrupt which is enabled by the MASK register
will set the IR bit (MSB) of the DATA register and bring the /IRQ pin
low. In a multi-chip system, the IR bit can be polled to detect which
chip has generated an interrupt request. The interrupt DATA register is
cleared and the /IRQ line returns high following a read of the DATA
register. Since each interrupt sets an interrupt bit regardless of the
MASK, and each interrupt bit can be selectively masked to prevent the
generation of a processor interrupt, it is possible to intermix polled
interrupts with true interrupts. However, polling the IR bit will cause
the DATA register to clear, therefore, it is up to the user to preserve
the information contained in the DATA register if any polled interrupts
were present.
The MASK register provides convenient control of individual mask bits.
When writing to the MASK register, if bit 7 (SET/CLEAR) of the data
APPENDIX M 433
~
written is a ZERO, any mask bit written with a one will be cleared, while
those mask bits written with a zero will be unaffected. If bit 7 of the
data written is a ONE, any mask bit written with a one will be set, while
those mask bits written with a zero will be unaffected. In order for an
interrupt flag to set IR and generate an Interrupt Request, the corre-
sponding MASK bit must be set.
READ (INT DATA)
REG NAME
+-----+---------+------+------+------+------+------+------+------+------+
| D | ICR | IR | 0 | 0 | FLG | SP | ALRM | TB | TA |
+-----+---------+------+------+------+------+------+------+------+------+
WRITE (INT MASK)
REG NAME
+-----+---------+------+------+------+------+------+------+------+------+
| D | ICR | S/C | X | X | FLG | SP | ALRM | TB | TA |
+-----+---------+------+------+------+------+------+------+------+------+
CONTROL REGISTERS
There are two control registers in the 6526, CRA and CRB. CRA is
associated with TIMER A and CRB is associated with TIMER B. The register
format is as follows:
CRA:
Bit Name Function
0 START 1=START TIMER A, 0=STOP TIMER A. This bit is automatically
reset when underflow occurs during one-shot mode.
1 PBON 1=TIMER A output appears on PB6, 0=PB6 normal operation.
2 OUTMODE 1=TOGGLE, 0=PULSE
3 RUNMODE 1=ONE-SHOT, 0=CONTINUOUS
4 LOAD 1=FORCE LOAD (this is a STROBE input, there is no data
storage, bit 4 will always read back a zero and writing a
zero has no effect).
5 INMODE 1=TIMER A counts positive CNT transitions, 0=TIMER A counts
02 pulses.
6 SPMODE 1=SERIAL PORT output (CNT sources shift clock),
0=SERIAL PORT input (external shift clock required).
7 TODIN 1=50 Hz clock required on TOD pin for accurate time,
0=60 Hz clock required on TOD pin for accurate time.
434 APPENDIX M
~
CRB:
Bit Name Function
(Bits CRB0-CRB4 are identical to CRA0-CRA4 for TIMER B with
the exception that bit 1 controls the output of TIMER B on
PB7).
5,6 INMODE Bits CRB5 and CRB6 select one of four input modes for
TIMER B as:
CRB6 CRB5
0 0 TIMER B counts 02 pulses.
0 1 TIMER B counts positive CNT transistions.
1 0 TIMER B counts TIMER A underflow pulses.
1 1 TIMER B counts TIMER A underflow pulses
while CNT is high.
7 ALARM 1=writing to TOD registers sets ALARM, 0=writing to TOD
registers sets TOD clock.
REGNAME TODIN SP MODE IN MODE LOAD RUN MODE OUT MODE PB ON START
+-+---+------+-------+-------+--------+-------+--------+--------+-------+
|E|CRA|0=60Hz|0=INPUT| 0=02 |1=FORCE |0=CONT.|0=PULSE |0=PB6OFF|0=STOP |
| | | | | | LOAD | | | | |
| | |1=50Hz|1=OUTP.| 1=CNT |(STROBE)|1=O.S. |1=TOGGLE|1=PB6ON |1=START|
+-+---+------+-------+-------+--------+-------+--------+--------+-------+
+------------------ TA ----------------------------+
REGNAME ALARM IN MODE LOAD RUN MODE OUT MODE PB ON START
+-+---+------+------+--------+--------+-------+--------+--------+-------+
|E|CRB|0=TOD | 0 |0=02 |1=FORCE |0=CONT.|0=PULSE |0=PB7OFF|0=STOP |
| | | | 1 |1=CNT |LOAD | | | | |
| | |1= | 1 |0=TA | | | | | |
| | | ALARM| 1 |1=CNT&TA|(STROBE)|1=O.S. |1=TOGGLE|1=PB7ON |1=START|
+-+---+------+------+--------+--------+-------+--------+--------+-------+
+-------------------------- TB ----------------------------+
All unused register bits are unaffected by a write and are forced to zero
on a read.
+-----------------------------------------------------------------------+
| COMMODORE SEMICONDUCTOR GROUP reserves the right to make changes to |
| any products herein to improve reliability, function or design. |
| COMMODORE SEMICONDUCTOR GROUP does not assume any liability arising |
| out of the application or use of any product or circuit described |
| herein; neither does it convey any license under its patent rights nor|
| the rights of others. |
+-----------------------------------------------------------------------+
APPENDIX M 435
~
APPENDIX N
6566/6567 (VIC-II) CHIP
SPECIFICATIONS
The 6566/6567 are multi-purpose color video controller devices for use
in both computer video terminals and video game applications. Both
devices contain 47 control registers which are accessed via a standard
8-bit microprocessor bus (65XX) and will access up to 16K of memory for
display information. The various operating modes and options within each
mode are described.
CHARACTER DISPLAY MODE
In the character display mode, the 6566/6567 fetches CHARACTER POINTERs
from the VIDEO MATRIX area of memory and translates the pointers to
character dot location addresses in the 2048 byte CHARACTER BASE area of
memory. The video matrix is comprised of 1000 consecutive locations in
memory which each contain an eight-bit character pointer. The location of
the video matrix within memory is defined by VM13-VM10 in register 24
($18) which are used as the 4 MSB of the video matrix address. The lower
order 10 bits are provided by an internal counter (VC9-VC0) which steps
through the 1000 character locations. Note that the 6566/6567 provides 14
address outputs; therefore, additional system hardware may be required
for complete system memory decodes.
CHARACTER POINTER ADDRESS
A13| A12| A11| A10| A09| A08| A07| A06| A05| A04| A03| A02| A01| A00
------+----+----+----+----+----+----+----+----+----+----+----+----+------
VM13|VM12|VM11|VM10| VC9| VC8| VC7| VC6| VC5| VC4| VC3| VC2| VC1| VC0
436 APPENDIX N
~
The eight-bit character pointer permits up to 256 different character
definitions to be available simultaneously. Each character is an 8*8 dot
matrix stored in the character base as eight consecutive bytes. The loca-
tion of the character base is defined by CB13-CB11 also in register 24
($18) which are used for the 3 most significant bits (MSB) of the char-
acter base address. The 11 lower order addresses are formed by the 8-bit
character pointer from the video matrix (D7-D0) which selects a
particular character, and a 3-bit raster counter (RC2-RC0) which selects
one of the eight character bytes. The resulting characters are formatted
as 25 rows of 40 characters each. In addition to the 8-bit character
pointer, a 4-bit COLOR NYBBLE is associated with each video matrix
location (the video matrix memory must be 12 bits wide) which defines one
of sixteen colors for each character.
CHARACTER DATA ADDRESS
A13| A12| A11| A10| A09| A08| A07| A06| A05| A04| A03| A02| A01| A00
------+----+----+----+----+----+----+----+----+----+----+----+----+------
CB13|CB12|CB11| D7 | D6 | D5 | D4 | D3 | D2 | D1 | D0 | RC2| RC1| RC0
STANDARD CHARACTER MODE (MCM = BMM = ECM = 0)
In the standard character mode, the 8 sequential bytes from the
character base are displayed directly on the 8 lines in each character
region. A "0" bit causes the background #0 color (from register 33 ($21))
to be displayed while the color selected by the color nybble (foreground)
is displayed for a "1" bit (see Color Code Table).
| CHARACTER |
FUNCTION | BIT | COLOR DISPLAYED
--------------+-----------+----------------------------------------------
Background | 0 | Background #0 color
| | (register 33 ($21)
Foreground | 1 | Color selected by 4-bit color nybble
Therefore, each character has a unique color determined by the 4-bit
color nybble (1 of 16) and all characters share the common background
color.
APPENDIX N 437
~
MULTI-COLOR CHARACTER MODE (MCM = 1, BMM = ECM = 0 )
Multi-color mode provides additional color flexibility allowing up to
four colors within each character but with reduced resolution. The multi-
color mode is selected by setting the MCM bit in register 22 ($16) to
"1," which causes the dot data stored in the character base to be
interpreted in a different manner. If the MSB of the color nybble is a
"0," the character will be displayed as described in standard character
mode, allowing the two modes to be inter-mixed (however, only the lower
order 8 colors are available). When the MSB of the color nybble is a "1"
(if MCM:MSB(CM) = 1) the character bits are interpreted in the multi-
color mode:
| CHARACTER |
FUNCTION | BIT PAIR | COLOR DISPLAYED
--------------+------------+---------------------------------------------
Background | 00 | Background #0 Color
| | (register 33 ($21))
Background | 01 | Background #1 Color
| | (register 34 ($22)
Foreground | 10 | Background #2 Color
| | (register 35 ($23)
Foreground | 11 | Color specified by 3 LSB
| | of color nybble
Since two bits are required to specify one dot color, the character is
now displayed as a 4*8 matrix with each dot twice the horizontal size as
in standard mode. Note, however, that each character region can now
contain 4 different colors, two as foreground and two as background (see
MOB priority).
EXTENDED COLOR MODE (ECM = 1, Bmm = MCM = 0)
The extended color mode allows the selection of individual, background
colors for each character region with the normal 8*8 character
resolution. This mode is selected by setting the ECM bit of register 17
($11) to "1". The character dot data is displayed as in the standard mode
(foreground color determined by the color nybble is displayed for a "1"
438 APPENDIX N
~
data bit), but the 2 MSB of the character pointer are used to select the
background color for each character region as follows:
CHAR. POINTER |
MS BIT PAIR | BACKGROUND COLOR DISPLAYED FOR 0 BIT
--------------------+----------------------------------------------------
00 | Background #0 color (register 33 ($21))
01 | Background #l color (register 34 ($22))
10 | Background #2 color (register 35 ($23))
11 | Background #3 color (register 36 ($24))
Since the two MSB of the character pointers are used for color informa-
tion, only 64 different character definitions are available. The 6566/
6567 will force CB10 and CB9 to "0" regardless of the original pointer
values, so that only the first 64 character definitions will be accessed.
With extended color mode each character has one of sixteen individually
defined foreground colors and one of the four available background
colors.
+-----------------------------------------------------------------------+
| NOTE: Extended color mode and multi-color mode should not be enabled |
| simultaneously. |
+-----------------------------------------------------------------------+
BIT MAP MODE
In bit map mode, the 6566/6567 fetches data from memory in a different
fashion, so that a one-to-one correspondence exists between each
displayed dot and a memory bit. The bit map mode provides a screen
resolution of 320H * 200V individually controlled display dots. Bit map
mode is selected by setting the BMM bit in register 17 ($11) to a "1".
The VIDEO MATRIX is still accessed as in character mode, but the video
matrix data is no longer interpreted as character pointers, but rather as
color data. The VIDEO MATRIX COUNTER is then also used as an address to
fetch the dot data for display from the 8000-byte DISPLAY BASE. The
display base address is formed as follows:
A13| A12| A11| A10| A09| A08| A07| A06| A05| A04| A03| A02| A01| A00
------+----+----+----+----+----+----+----+----+----+----+----+----+------
CB13| VC9| VC8| VC7| VC6| VC5| VC4| VC3| VC2| VC1| VC0| RC2| RC1| RC0
APPENDIX N 439
~
VCx denotes the video matrix counter outputs, RCx denotes the 3-bit
raster line counter and CB13 is from register 24 ($18). The video matrix
counter steps through the same 40 locations for eight raster lines, con-
tinuing to the next 40 locations every eighth line, while the raster
counter increments once for each horizontal video line (raster line).
This addressing results in each eight sequential memory locations being
formatted as an 8*8 dot block on the video display.
STANDARD BIT MAP MODE (BMM =1, MCM = 0)
When standard bit map mode is in use, the color information is derived
only from the data stored in the video matrix (the color nybble is
disregarded). The 8 bits are divided into two 4-bit nybbles which allow
two colors to be independently selected in each 8*8 dot block. When a bit
in the display memory is a "0" the color of the output dot is set by the
least significant (lower) nybble (LSN). Similarly, a display memory bit
of "1" selects the output color determined by the MSN (upper nybble).
BIT | DISPLAY COLOR
-----------+-------------------------------------------------------------
0 | Lower nybble of video matrix pointer
1 | Upper nybble of video matrix pointer
MULTI-COLOR BIT MAP MODE (BMM = MCM = 1)
Multi-colored bit map mode is selected by setting the MCM bit in
register 22 ($16) to a "1" in conjunction with the BMM bit. Multi-color
mode uses the same memory access sequences as standard bit map mode, but
interprets the dot data as follows:
BIT PAIR | DISPLAY COLOR
--------------------+----------------------------------------------------
00 | Background #0 color (register 33 ($21))
01 | Upper nybble of video matrix pointer
10 | Lower nybble of video matrix pointer
11 | Video matrix color nybble
Note that the color nybble (DB11-DB8) IS used for the multi-color bit map
mode. Again, as two bits are used to select one dot color, the horizontal
440 APPENDIX N
~
dot size is doubled, resulting in a screen resolution of 160H*200V.
Utilizing multi-color bit map mode, three independently selected colors
can be displayed in each 8*8 block in addition to the background color.
MOVABLE OBJECT BLOCKS
The movable object block (MOB) is a special type of character which can
be displayed at any one position on the screen without the block
constraints inherent in character and bit map mode. Up to 8 unique MOBs
can be displayed simultaneously, each defined by 63 bytes in memory which
are displayed as a 24*21 dot array (shown below). A number of special
features make MOBs especially suited for video graphics and game
applications.
MOB DISPLAY BLOCK
+--------+--------+--------+
| BYTE | BYTE | BYTE |
+--------+--------+--------+
| 00 | 01 | 02 |
| 03 | 04 | 05 |
| . | . | . |
| . | . | . |
| . | . | . |
| 57 | 58 | 59 |
| 60 | 61 | 62 |
+--------+--------+--------+
ENABLE
Each MOB can be selectively enabled for display by setting its corre-
sponding enable bit (MnE) to "1" in register 21 ($15). If the MnE bit is
"0," no MOB operations will occur involving the disabled MOB.
POSlTlON
Each MOB is positioned via its X and Y position register (see register
map) with a resolution of 512 horizontal and 256 vertical positions. The
APPENDIX N 441
~
position of a MOB is determined by the upper-left corner of the array. X
locations 23 to 347 ($17-$157) and Y locations 50 to 249 ($32-$F9) are
visible. Since not all available MOB positions are entirely visible on
the screen, MOBs may be moved smoothly on and off the display screen.
COLOR
Each MOB has a separate 4-bit register to determine the MOB color. The
two MOB color modes are:
STANDARD MOB (MnMC = 0)
In the standard mode, a "0" bit of MOB data allows any background data
to show through (transparent) and a "1" bit is displayed as the MOB color
determined by the corresponding MOB Color register.
MULTI-COLOR MOB (MnMC = 1)
Each MOB can be individually selected as a multi-color MOB via MnMC
bits in the MOB Multi-color register 28 ($1C). When the MnMC bit is "1",
the corresponding MOB is displayed in the multi-color mode. In the multi-
color mode, the MOB data is interpreted in pairs (similar to the other
multi-color modes) as follows:
BIT PAIR | COLOR DISPLAYED
--------------------+----------------------------------------------------
00 | Transparent
01 | MOB Multi-color #0 (register 37 ($25))
10 | MOB Color (registers 39-46 ($27-$2E))
11 | MOB Multi-color #1 (register 38 ($26))
Since two bits of data are required for each color, the resolution of the
MOB is reduced to 12X21, with each horizontal dot expanded to twice
standard size so that the overall MOB size does not change. Note that up
to 3 colors can be displayed in each MOB (in addition to transparent) but
that two of the colors are shared among all the MOBs in the multi-color
mode.
442 APPENDIX N
~
MAGNIFICATION
Each MOB can be selectively expanded (2X) in both the horizontal and
vertical directions. Two registers contain the control bits (MnXE,MnYE)
for the magnification control.
REGISTER | FUNCTION
------------+------------------------------------------------------------
23 ($17) | Horizontal expand MnXE-"1"=expand; "0"=normal
29 ($1D) | Vertical expand MnYE-"1"=expand; "0"=normal
When MOBs are expanded, no increase in resolution is realized. The same
24*21 array (12X21 if multi-colored) is displayed, but the overall MOB
dimension is doubled in the desired direction (the smallest MOB dot may
be up to 4X standard dot dimension if a MOB is both multi-colored and
expanded).
PRIORITY
The priority of each MOB may be individually controlled with respect to
the other displayed information from character or bit map modes. The
priority of each MOB is set by the corresponding bit (MnDP) of register
27 ($1B) as follows:
REG BIT | PRIORITY TO CHARACTER OR BIT MAP DATA
------------+------------------------------------------------------------
0 | Non-transparent MOB data will be displayed (MOB in front)
1 | Non-transparent MOB data will be displayed only instead of
| Bkgd #0 or multi-color bit pair 01 (MOB behind)
MOB-DISPLAY DATA PRIORITY
+--------------+--------------+
| MnDP = 1 | MnDP = 0 |
+--------------+--------------+
| MOBn | Foreground |
| Foreground | MOBn |
| Background | Background |
+--------------+--------------+
APPENDIX N 443
~
MOB data bits of "0" ("00" in multi-color mode) are transparent, always
permitting any other information to be displayed.
The MOBs have a fixed priority with respect to each other, with MOB 0
having the highest priority and MOB 7 the lowest. When MOB data (except
transparent data) of two MOBs are coincident, the data from the lower
number MOB will be displayed. MOB vs. MOB data is prioritized before
priority resolution with character or bit map data.
COLLISION DETECTION
Two types of MOB collision (coincidence) are detected, MOB to MOB
collision and MOB to display data collision:
1) A collision between two MOBs occurs when non-transparent output data
of two MOBs are coincident. Coincidence of MOB transparent areas
will not generate a collision. When a collision occurs, the MOB bits
(MnM) in the MOB-MOB COLLISION register 30 ($1E) will be set to "1"
for both colliding MOBS. As a collision between two (or more) MOBs
occurs, the MOB-MOB collision bit for each collided MOB will be set.
The collision bits remain set until a read of the collision
register, when all bits are automatically cleared. MOBs collisions
are detected even if positioned off-screen.
2) The second type of collision is a MOB-DATA collision between a MOB
and foreground display data from the character or bit map modes. The
MOB-DATA COLLISION register 31 ($1F) has a 'bit (MnD) for each MOB
which is set to "1" when both the MOB and non-background display
data are coincident. Again, the coincidence of only transparent data
does not generate a collision. For special applications, the display
data from the 0-1 multicolor bit pair also does not cause a
collision. This feature permits their use as background display data
without interfering with true MOB collisions. A MOB-DATA collision
can occur off-screen in the horizontal direction if actual display
data has been scrolled to an off-screen position (see scrolling).
The MOB-DATA COLLISION register also automatically clears when read.
444 APPENDIX N
~
The collision interrupt latches are set whenever the first bit of
either register is set to "1". Once any collision bit within a register
is set high, subsequent collisions will not set the interrupt latch
until that collision register has been cleared to all "0s" by a read.
MOB MEMORY ACCESS
The data for each MOB is Stored in 63 consecutive bytes of memory. Each
block of MOB data is defined by a MOB pointer, located at the end of the
VIDEO MATRIX. Only 1000 bytes of the video matrix are used in the normal
display modes, allowing the video matrix locations 1016-1023 (VM base+
$3F8 to VM base+$3FF) to be used for MOB pointers 0-7, respectively. The
eight-bit MOB pointer from the video matrix together with the six bits
from the MOB byte counter (to address 63 bytes) define the entire 14-bit
address field:
A13| A12| A11| A10| A09| A08| A07| A06| A05| A04| A03| A02| A01| A00
------+----+----+----+----+----+----+----+----+----+----+----+----+------
MP7| MP6| MP5| MP4| MP3| MP2| MP1| MP0| MC5| MC4| MC3| MC2| MC1| MC0
Where MPx are the MOB pointer bits from the video matrix and MCx are the
internally generated MOB counter bits. The MOB pointers are read from the
video matrix at the end of every raster line. When the Y position
register of a MOB matches the current raster line count, the actual
fetches of MOB data begin. Internal counters automatically step through
the 63 bytes of MOB data, displaying three bytes on each raster line.
OTHER FEATURES
SCREEN BLANKING
The display screen may be blanked by setting the DEN bit in register
17 ($11) to a "0". When the screen is blanked, the entire screen will be
filled with the exterior color as set in register 32 ($20). When blanking
is active, only transparent (Phase 1) memory accesses are required, per-
mitting full processor utilization of the system bus. MOB data, however,
will be accessed if the MOBs are not also disabled. The DEN bit must be
set to "1" for normal video display.
APPENDIX N 445
~
ROW/COLUMN SELECT
The normal display consists of 25 rows of 40 characters (or character
regions) per row. For special display purposes, the display window may be
reduced to 24 rows and 38 characters. There is no change in the format of
the displayed information, except that characters (bits) adjacent to the
exterior border area will now be covered by the border. The select bits
operate as follows:
RSEL | NUMBER OF ROWS | CSEL | NUMBER OF COLUMNS
-------+----------------------------+-------+----------------------------
0 | 24 rows | 0 | 38 columns
1 | 25 rows | 1 | 40 columns
The RSEL bit is in register 17 ($11) and the CSEL bit is in register 22
($16). For standard display the larger display window is normally used,
while the smaller display window is normally used in conjunction with
scrolling.
SCROLLING
The display data may be scrolled up to one entire character space in
both the horizontal and vertical direction. When used in conjunction with
the smaller display window (above), scrolling can be used to create a
smooth panning motion of display data while updating the system memory
only when a new character row (or column) is required. Scrolling is also
used to center a fixed display within the display window.
BITS | REGISTER | FUNCTION
----------------------+--------------------+-----------------------------
X2,X1,X0 | 22 ($16) | Horizontal Position
Y2,Y1,Y0 | 17 ($11) | Vertical Position
LIGHT PEN
The light pen input latches the current screen position into a pair of
registers (LPX,LPY) on a low-going edge. The X position register 19 ($13)
will contain the 8 MSB of the X position at the time of transition. Since
the X position is defined by a 512-state counter (9 bits) resolution to 2
horizontal dots is provided. Similarly, the Y position is latched to its
446 APPENDIX N
~
register 20 ($14) but here 8 bits provide single raster resolution within
the visible display. The light pen latch may be triggered only once per
frame, and subsequent triggers within the same frame will have no effect.
Therefore, you must take several samples before turning the light pen to
the screen (3 or more samples, average), depending upon the
characteristics of your light pen.
RASTER REGISTER
The raster register is a dual-function register. A read of the raster
register 18 ($12) returns the lower 8 bits of the current raster position
(the MSB-RC8 is located in register 17 ($11)). The raster register can be
interrogated to implement display changes outside the visible area to
prevent display flicker. The visible display window is from raster 51
through raster 251 ($033-$0FB). A write to the raster bits (including
RC8) is latched for use in an internal raster compare. When the current
raster matches the written value, the raster interrupt latch is set.
INTERRUPT REGISTER
The interrupt register shows the status of the four sources of
interrupt. An interrupt latch in register 25 ($19) is set to "1" when an
interrupt source has generated an interrupt request. The four sources of
interrupt are:
LATCH |ENABLE|
BIT | BIT | WHEN SET
-------+------+----------------------------------------------------------
IRST | ERST | Set when (raster count) = (stored raster count)
IMDC | EMDC | Set by MOB-DATA collision register (first collision only)
IMMC | EMMC | Set by MOB-MOB collision register (first collision only)
ILP | ELP | Set by negative transition of LP input (once per frame)
IRQ | | Set high by latch set and enabled (invert of /IRQ output)
To enable an interrupt request to set the /IRQ output to "0", the
corresponding interrupt enable bit in register 26 ($1A) must be set to
"1". Once an interrupt latch has been set, the latch may be cleared only
by writing a "1" to the desired latch in the interrupt register. This
feature allows selective handling of video interrupts without software
required to "remember" active interrupts.
APPENDIX N 447
~
DYNAMIC RAM REFRESH
A dynamic ram refresh controller is built in to the 6566/6567 devices.
Five 8-bit row addresses are refreshed every raster line. This rate
guarantees a maximum delay of 2.02 ms between the refresh of any single
row address in a 128 refresh scheme. (The maximum delay is 3.66 ms in a
256 address refresh scheme.) This refresh is totally transparent to the
system, since the refresh occurs during Phase 1 of the system clock. The
6567 generates both /RAS and /CAS which are normally connected directly
to the dynamic rams. /RAS and /CAS are generated for every Phase 2 and
every video data access (including refresh) so that external clock
generation is not required.
RESET
THEORY OF OPERATION
SYSTEM INTERFACE
The 6566/6567 video controller devices interact with the system data
bus in a special way. A 65XX system requires the system buses only during
the Phase 2 (clock high) portion of the cycle. The 6566/6567 devices take
advantage of this feature by normally accessing system memory during the
Phase 1 (clock low) portion of the clock cycle. Therefore, operations
such as character data fetches and memory refresh are totally transparent
to the processor and do not reduce the processor throughput. The video
chips provide the interface control signals required to maintain this bus
sharing.
The video devices provide the signal AEC (address enable control) which
is used to disable the processor address bus drivers allowing the video
device to access the address bus. AEC is active low which, permits direct
connection to the AEC input of the 65XX family. The AEC signal is
448 APPENDIX N
~
normally activated during Phase 1 so that processor operation is not
affected. Because of this bus "sharing", all memory accesses must be
completed in 1/2 cycle. Since the video chips provide a 1-MHz clock
(which must be used as system Phase 2), a memory cycle is 500 ns
including address setup, data access and, data setup to the reading
device.
Certain operations of the 6566/6567 require data at a faster rate than
available by reading only during the Phase 1 time; specifically, the ac-
cess of character pointers from the video matrix and the fetch of MOB
data. Therefore, the processor must be disabled and the data accessed
during the Phase 2 clock. This is accomplished via the BA (bus available)
signal. The BA line is normally high but is brought low during Phase 1 to
indicate that the video chip will require a Phase 2 data access. Three
Phase-2 times are allowed after BA low for the processor to complete any
current memory accesses. On the fourth Phase 2 after BA low, the AEC
signal will remain low during Phase 2 as the video chip fetches data. The
BA line is normally connected to the RDY input of a 65XX processor. The
character pointer fetches occur every eighth raster line during the
display window and require 40 consecutive Phase 2 accesses to fetch the
video matrix pointers. The MOB data fetches require 4 memory accesses as
follows:
PHASE | DATA | CONDITION
--------+-------------+--------------------------------------------------
1 | MOB Pointer | Every raster
2 | MOB Byte 1 | Each raster while MOB is displayed
1 | MOB Byte 2 | Each raster while MOB is displayed
2 | MOB Byte 3 | Each raster while MOB is displayed
The MOB pointers are fetched every other Phase 1 at the end of each
raster line. As required, the additional cycles are used for MOB data
fetches. Again, all necessary bus control is provided by the 6566/6567
devices.
MEMORY INTERFACE
The two versions of the video interface chip, 6566 and 6567, differ in
address output configurations. The 6566 has thirteen fully decoded
APPENDIX N 449
~
addresses for direct connection to the system address bus. The 6567 has
multiplexed addresses for direct connection to 64K dynamic RAMS. The
least significant address bits, A06-A00, are present on A06-A00 while
/RAS is brought low, while the most significant bits, A13-A08, are pres-
ent on A05-A00 while /CAS is brought low. The pins A11-A07 on the 6567
are static address outputs to allow direct connection of these bits to a
conventional 16K (2K*8) ROM. (The lower order addresses require external
latching.)
PROCESSOR INTERFACE
Aside from the special memory accesses described above, the 6566/6567
registers can be accessed similar to any other peripheral device. The
following processor interface signals are provided:
DATA BUS (DB7-DB0)
The eight data bus pins are the bidirectional data port, controlled by
/CS, RW, and Phase 0. The data bus can only be accessed while AEC and
Phase 0 are high and /CS is low.
CHIP SELECT (/CS)
The chip select pin, /CS, is brought low to enable access to the device
registers in conjunction with the address and RW pins. /CS low is recog-
nized only while AEC and Phase 0 are high.
READ/WRITE (R/W)
The read/write input, R/W, is used to determine the direction of data
transfer on the data bus, in conjunction with /CS. When R/W is high ("1")
data is transferred from the selected register to the data bus output.
When R/W is low ("0") data presented on the data bus pins is loaded into
the selected register.
ADDRESS BUS (A05-A00)
The lower six address pins, A5-A0, are bidirectional. During a pro-
cessor read or write of the video device, these address pins are inputs.
The data on the address inputs selects the register for read or write as
defined in the register map.
450 APPENDIX N
~
CLOCK OUT (PH0)
The clock output, Phase 0, is the 1-MHz clock used as the 65XX pro-
cessor Phase 0 in. All system bus activity is referenced to this clock.
The clock frequency is generated by dividing the 8-MHz video input clock
by eight.
INTERRUPTS (/IRQ)
The interrupt output, /IRQ, is brought low when an enabled source of
interrupt occurs within the device. The /IRQ output is open drain,
requiring an external pull-up resistor.
VIDEO INTERFACE
The video output signal from the 6566/6567 consists of two signals
which must be externally mixed together. SYNC/LUM output contains all the
video data, including horizontal and vertical syncs, as well as the
luminance information of the video display. SYNC/LUM is open drain,
requiring an external pull-up of 500 ohms. The COLOR output contains all
the chrominance information, including the color reference burst and the
color of all display data. The COLOR output is open source and should be
terminated with 1000 ohms to ground. After appropriate mixing of these
two signals, the resulting signal can directly drive a video monitor or
be fed to a modulator for use with a standard television.
SUMMARY OF 6566/6567 BUS ACTIVITY
+-----+-----+-----+-----+-----------------------------------------------+
| AEC | PH0 | /CS | R/W | ACTION |
+-----+-----+-----+-----+-----------------------------------------------+
| 0 | 0 | X | X | PHASE 1 FETCH, REFRESH |
| 0 | 1 | X | X | PHASE 2 FETCH (PROCESSOR OFF) |
| 1 | 0 | X | X | NO ACTION |
| 1 | 1 | 0 | 0 | WRITE TO SELECTED REGISTER |
| 1 | 1 | 0 | 1 | READ FROM SELECTED REGISTER |
| 1 | 1 | 1 | X | NO ACTION |
+-----+-----+-----+-----+-----------------------------------------------+
APPENDIX N 451
~
PIN CONFIGURATION
+----+ +----+
D6 1 @| +-+ |@ 40 Vcc
| |
D5 2 @| |@ 39 D7
| |
D4 3 @| |@ 38 D8
| |
D3 4 @| |@ 37 D9
| |
D2 5 @| |@ 36 D10
| |
D1 6 @| |@ 35 D11
| |
D0 7 @| |@ 34 A10
| |
/IRQ 8 @| |@ 33 A9
| |
LP 9 @| |@ 32 A8
| |
/CS 10 @| |@ 31 A7
| 6567 |
R/W 11 @| |@ 30 A6("1")
| |
BA 12 @| |@ 29 A5(A13)
| |
Vdd 13 @| |@ 28 A4(A12)
| |
COLOR 14 @| |@ 27 A3(A11)
| |
S/LUM 15 @| |@ 26 A2(A10)
| |
AEC 16 @| |@ 25 A1(A9)
| |
PH0 17 @| |@ 24 A0(A8)
| |
/RAS 18 @| |@ 23 A11
| |
/CAS 19 @| |@ 22 PHIN
| |
Vss 20 @| |@ 21 PHCL
+-----------+
452 APPENDIX N (Multiplexed addresses in parentheses)
~
PIN CONFIGURATION
+----+ +----+
D6 1 @| +-+ |@ 40 Vcc
| |
D5 2 @| |@ 39 D7
| |
D4 3 @| |@ 38 D8
| |
D3 4 @| |@ 37 D9
| |
D2 5 @| |@ 36 D10
| |
D1 6 @| |@ 35 D11
| |
D0 7 @| |@ 34 A13
| |
/IRQ 8 @| |@ 33 A12
| |
LP 9 @| |@ 32 A11
| |
/CS 10 @| |@ 31 A10
| 6567 |
R/W 11 @| |@ 30 A9
| |
BA 12 @| |@ 29 A8
| |
Vdd 13 @| |@ 28 A7
| |
COLOR 14 @| |@ 27 A6
| |
S/LUM 15 @| |@ 26 A5
| |
AEC 16 @| |@ 25 A4
| |
PH0 17 @| |@ 24 A3
| |
PHIN 18 @| |@ 23 A2
| |
PHCOL 19 @| |@ 22 A1
| |
Vss 20 @| |@ 21 A0
+-----------+
APPENDIX N 453
~
REGISTER MAP
+----------+------------------------------------------------------------+
| ADDRESS | DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 DESCRIPTION |
+----------+------------------------------------------------------------+
| 00 ($00) | M0X7 M0X6 M0X5 M0X4 M0X3 M0X2 M0X1 M0X0 MOB 0 X-position |
| 01 ($01) | M0Y7 M0Y6 M0Y5 M0Y4 M0Y3 M0Y2 M0Y1 M0Y0 MOB 0 Y-position |
| 02 ($02) | M1X7 M1X6 M1X5 M1X4 M1X3 M1X2 M1Xl M1X0 MOB 1 X-position |
| 03 ($03) | M1Y7 M1Y6 M1Y5 M1Y4 M1Y3 M1Y2 M1Y1 M1Y0 MOB 1 Y-position |
| 04 ($04) | M2X7 M2X6 M2X5 M2X4 M2X3 M2X2 M2X1 M2X0 MOB 2 X-position |
| 05 ($05) | M2Y7 M2Y6 M2Y5 M2Y4 M2Y3 M2Y2 M2Y1 M2Y0 MOB 2 Y-position |
| 06 ($06) | M3X7 M3X6 M3X5 M3X4 M3X3 M3X2 M3X1 M3X0 MOB 3 X-position |
| 07 ($07) | M3Y7 M3Y6 M3Y5 M3Y4 M3Y3 M3Y2 M3Y1 M3Y0 MOB 3 Y-position |
| 08 ($08) | M4X7 M4X6 M4X5 M4X4 M4X3 M4X2 M4X1 M4X0 MOB 4 X-position |
| 09 ($09) | M4Y7 M4Y6 M4Y5 M4Y4 M4Y3 M4Y2 M4Y1 M4Y0 MOB 4 Y-position |
| 10 ($0A) | M5X7 M5X6 M5X5 M5X4 M5X3 M5X2 M5X1 M5X0 MOB 5 X-position |
| 11 ($0B) | M5Y7 M5Y6 M5Y5 M5Y4 M5Y3 M5Y2 M5Y1 M5Y0 MOB 5 Y-position |
| 12 ($0C) | M6X7 M6X6 M6X5 M6X4 M6X3 M6X2 M6X1 M6X0 MOB 6 X-position |
| 13 ($0D) | M6Y7 M6Y6 M6Y5 M6Y4 M6Y3 M6Y2 M6Y1 M6Y0 MOB 6 Y-position |
| 14 ($0E) | M7X7 M7X6 M7X5 M7X4 M7X3 M7X2 M7Xl M7X0 MOB 7 X-position |
| 15 ($0F) | M7Y7 M7Y6 M7Y5 M7Y4 M7Y3 M7Y2 M7Y1 M6Y0 MOB 7 Y-position |
| 16 ($10) | M7X8 M6X8 M5X8 M4X8 M3X8 M2X8 M1X8 M0X8 MSB of X-position |
| 17 ($11) | RC8 ECM BMM DEN RSEL Y2 Y1 Y0 See text |
| 18 ($12) | RC7 RC6 RC5 RC4 RC3 RC2 RC1 RC0 Raster register |
| 19 ($13) | LPX8 LPX7 LPX6 LPX5 LPX4 LPX3 LPX2 LPX1 Light Pen X |
| 20 ($14) | LPY7 LPY6 LPY5 LPY4 LPY3 LPY2 LPY1 LPY0 Light Pen Y |
| 21 ($15) | M7E M6E M5E M4E M3E M2E M1E M0E MOB Enable |
| 22 ($16) | - - RES MCM CSEL X2 X1 X0 See text |
| 23 ($17) | M7YE M6YE M5YE M4YE M3YE M2YE M1YE M0YE MOB Y-expand |
454 APPENDIX N
~
| 24 ($18) | VM13 VM12 VM11 VM10 CB13 CB12 CB11 - Memory Pointers |
| 25 ($19) | IRQ - - - ILP IMMC IMBC IRST Interrupt Register|
| 26 ($1A) | - - - - ELP EMMC EMBC ERST Enable Interrupt |
| 27 ($1B) | M7DP M6DP M5DP M4DP M3DP M2DP M1DP M0DP MOB-DATA Priority |
| 28 ($1C) | M7MC M6MC M5MC M4MC M3MC M2MC M1MC M0MC MOB Multicolor Sel|
| 29 ($1D) | M7XE M6XE M5XE M4XE M3XE M2XE M1XE M0XE MOB X-expand |
| 30 ($1E) | M7M M6M M5M M4M M3M M2M M1M M0M MOB-MOB Collision |
| 31 ($1F) | M7D M6D M5D M4D M3D M2D M1D M0D MOB-DATA Collision|
| 32 ($20) | - - - - EC3 EC2 EC1 EC0 Exterior Color |
| 33 ($21) | - - - - B0C3 B0C2 B0C1 B0C0 Bkgd #0 Color |
| 34 ($22) | - - - - B1C3 B1C2 B1C1 B1C0 Bkgd #1 Color |
| 35 ($23) | - - - - B2C3 B2C2 B2C1 B2C0 Bkgd #2 Color |
| 36 ($24) | - - - - B3C3 B3C2 B3C1 B3C0 Bkgd #3 Color |
| 37 ($25) | - - - - MM03 MM02 MM01 MM00 MOB Multicolor #0 |
| 38 ($26) | - - - - MM13 MM12 MM11 MM10 MOB Multicolor #1 |
| 39 ($27) | - - - - M0C3 M0C2 M0C1 M0C0 MOB 0 Color |
| 40 ($28) | - - - - M1C3 M1C2 M1C1 M1C0 MOB 1 Color |
| 41 ($29) | - - - - M2C3 M2C2 M2C1 M2C0 MOB 2 Color |
| 42 ($2A) | - - - - M3C3 M3C2 M3C1 M3C0 MOB 3 Color |
| 43 ($2B) | - - - - M4C3 M4C2 M4C1 M4C0 MOB 4 Color |
| 44 ($2C) | - - - - M5C3 M5C2 M5C1 M5C0 MOB 5 Color |
| 45 ($2D) | - - - - M6C3 M6C2 M6C1 M6C0 MOB 6 Color |
| 46 ($2E) | - - - - M7C3 M7C2 M7C1 M7C0 MOB 7 Color |
+----------+------------------------------------------------------------+
+-----------------------------------------------------------------------+
| NOTE: A dash indicates a no connect. All no connects are read as a |
| "1" |
+-----------------------------------------------------------------------+
APPENDIX N 455
~
COLOR CODES
+--------+--------+--------+--------+--------+--------+-----------------+
| D3 | D2 | D1 | D0 | HEX | DEC | COLOR |
+--------+--------+--------+--------+--------+--------+-----------------+
| 0 | 0 | 0 | 0 | 0 | 0 | BLACK |
| 0 | 0 | 0 | 1 | 1 | 1 | WHITE |
| 0 | 0 | 1 | 0 | 2 | 2 | RED |
| 0 | 0 | 1 | 1 | 3 | 3 | CYAN |
| 0 | 1 | 0 | 0 | 4 | 4 | PURPLE |
| 0 | 1 | 0 | 1 | 5 | 5 | GREEN |
| 0 | 1 | 1 | 0 | 6 | 6 | BLUE |
| 0 | 1 | 1 | 1 | 7 | 7 | YELLOW |
| 1 | 0 | 0 | 0 | 8 | 8 | ORANGE |
| 1 | 0 | 0 | 1 | 9 | 9 | BROWN |
| 1 | 0 | 1 | 0 | A | 10 | LT RED |
| 1 | 0 | 1 | 1 | B | 11 | DARK GREY |
| 1 | 1 | 0 | 0 | C | 12 | MED GREY |
| 1 | 1 | 0 | 1 | 0 | 13 | LT GREEN |
| 1 | 1 | 1 | 0 | E | 14 | LT BLUE |
| 1 | 1 | 1 | 1 | F | 15 | LT GREY |
+--------+--------+--------+--------+--------+--------+-----------------+
456 APPENDIX N
~
APPENDIX O
6581 SOUND INTERFACE DEVICE (SID)
CHIP SPECIFICATIONS
CONCEPT
The 6581 Sound Interface Device (SID) is a single-chip, 3-voice elec-
tronic music synthesizer/sound effects generator compatible with the 65XX
and similar microprocessor families. SID provides wide-range, high-
resolution control of pitch (frequency), tone color (harmonic content),
and dynamics (volume). Specialized control circuitry minimizes software
overhead, facilitating use in arcade/home video games and low-cost
musical instruments.
FEATURES
o 3 TONE OSCILLATORS
Range: 0-4 kHz
o 4 WAVEFORMS PER OSCILLATOR
Triangle, Sawtooth,
Variable Pulse, Noise
o 3 AMPLITUDE MODULATORS
Range: 48 dB
o 3 ENVELOPE GENERATORS
Exponential response
Attack Rate: 2 ms-8 s
Decay Rate: 6 ms-24 s
Sustain Level: 0-peak volume
Release Rate: 6 ms-24 s
o OSCILLATOR SYNCHRONIZATION
o RING MODULATION
o PROGRAMMABLE FILTER
Cutoff range: 30 Hz-12 kHz
12 dB/octave Rolloff
Low pass, Bandpass,
High pass, Notch outputs
Variable Resonance
APPENDIX O 457
~
o MASTER VOLUME CONTROL
o 2 A/D POT INTERFACES
o RANDOM NUMBER/MODULATION GENERATOR
o EXTERNAL AUDIO INPUT
PIN CONFIGURATION
+----+ +----+
CAP1A 1 @| +-+ |@ 28 Vdd
| |
CAP1B 2 @| |@ 27 AUDIO OUT
| |
CAP2A 3 @| |@ 26 EXT IN
| |
CAP2B 4 @| |@ 25 Vcc
| |
/RES 5 @| |@ 24 POT X
| |
02 6 @| |@ 23 POT Y
| |
R/W 7 @| |@ 22 D7
| 6581 |
/CS 8 @| SID |@ 21 D6
| |
A0 9 @| |@ 20 D5
| |
A1 10 @| |@ 19 D4
| |
A2 11 @| |@ 18 D3
| |
A3 12 @| |@ 17 D2
| |
A4 13 @| |@ 16 D1
| |
GND 14 @| |@ 15 D0
+-----------+
458 APPENDIX O
~
[THE PICTURE IS MISSING!]
6581 BLOCK DIAGRAM
APPENDIX O 459
~
DESCRIPTION
The 6581 consists of three synthesizer "voices" which can be used
independently or in conjunction with each other (or external audio
sources) to create complex sounds. Each voice consists of a Tone
Oscillator/Waveform Generator, an Envelope Generator and an Amplitude
Modulator. The Tone Oscillator controls the pitch of the voice over a
wide range. The Oscillator produces four waveforms at the selected
frequency, with the unique harmonic content of each waveform providing
simple control of tone color. The volume dynamics of the oscillator are
controlled by the Amplitude Modulator under the direction of the Envelope
Generator. When triggered, the Envelope Generator creates an amplitude
envelope with programmable rates of increasing and decreasing volume. In
addition to the three voices, a programmable Filter is provided for
generating complex, dynamic tone colors via subtractive synthesis.
SID allows the microprocessor to read the changing output of the third
Oscillator and third Envelope Generator. These outputs can be used as a
source of modulation information for creating vibrato, frequency/filter
sweeps and similar effects. The third oscillator can also act as a random
number generator for games. Two A/D converters are provided for inter-
facing SID with potentiometers. These can be used for "paddles" in a
game environment or as front panel controls in a music synthesizer. SID
can process external audio signals, allowing multiple SID chips to be
daisy-chained or mixed in complex polyphonic systems.
SID CONTROL REGISTERS
There are 29 eight-bit registers in SID which control the generation of
sound. These registers are either WRITE-only or READ-only and are listed
below in Table 1.
460 APPENDIX O
~
Table 1. SID Register Map WO=WRITE-ONLY
RO=READ-ONLY
REG# DATA
(HEX) D7 D6 D5 D4 D3 D2 D1 D0 REG NAME REG
Voice 1 TYPE
0 00 F7 F6 F5 F4 F3 F2 F1 F0 FREQ LO WO
1 01 F15 F14 F13 F12 F11 F10 F9 F8 FREQ HI WO
2 02 PW7 PW6 PW5 PW4 PW3 PW2 PW1 PW0 PW LO WO
3 03 - - - - PW11 PW10 PW9 PW8 PW HI WO
4 04 NOISE PULSE SAW TRIANG TEST RING SYNC GATE CONTROL REG WO
5 05 ATK3 ATK2 ATK1 ATK0 DCY3 DCY2 DCY1 DCY0 ATTACK/DECAY WO
6 06 STN3 STN2 STN1 STN0 RLS3 RLS2 RLS1 RLS0 SUSTAIN/RELEASE WO
Voice 2
7 07 F7 F6 F5 F4 F3 F2 F1 F0 FREQ LO WO
8 08 F15 F14 F13 F12 F11 F10 F9 F8 FREQ HI WO
9 09 PW7 PW6 PW5 PW4 PW3 PW2 PW1 PW0 PW LO WO
10 0A - - - - PW11 PW10 PW9 PW8 PW HI WO
11 0B NOISE PULSE SAW TRIANG TEST RING SYNC GATE CONTROL REG WO
12 0C ATK3 ATK2 ATK1 ATK0 DCY3 DCY2 DCY1 DCY0 ATTACK/DECAY WO
13 0D STN3 STN2 STN1 STN0 RLS3 RLS2 RLS1 RLS0 SUSTAIN/RELEASE WO
Voice 3
14 0E F7 F6 F5 F4 F3 F2 F2 F1 FREQ LO WO
15 0F F15 F14 F13 F12 F11 F10 F9 F8 FREQ HI WO
16 10 PW7 PW6 PW5 PW4 PW3 PW2 PW1 PW0 PW LO WO
17 11 - - - - PW11 PW10 PW9 PW8 PW HI WO
18 12 NOISE PULSE SAW TRIANG TEST RING SYNC GATE CONTROL REG WO
19 13 ATK3 ATK2 ATK1 ATK0 DCY3 DCY2 DCY1 DCY0 ATTACK/DECAY WO
20 14 STN3 STN2 STN1 STN0 RLS3 RLS2 RLS1 RLS0 SUSTAIN/RELEASE WO
Filter
21 15 - - - - - FC2 FC1 FC0 FC LO WO
22 16 FC10 FC9 FC8 FC7 FC6 FC5 FC4 FC3 FC HI WO
23 17 RES3 RES2 RES1 RES0 FILTEX FILT3 FILT2 FILT1 RES/FILT WO
24 18 3OFF HP BP LP VOL3 VOL2 VOL1 VOL0 MODE/VOL WO
Misc.
25 19 PX7 PX6 PX5 PX4 PX3 PX2 PX1 PX0 POT X RO
26 1A PY7 PY6 PY5 PY4 PY3 PY2 PY1 PY0 POT Y RO
27 1B O7 O6 O5 O4 O3 O2 O1 O0 OSC3/RANDOM RO
28 1C E7 E6 E5 E4 E3 E2 E1 E0 ENV3 RO
APPENDIX O 461
~
SID REGISTER DESCRIPTION
VOICE 1
FREQ LO/FREQ HI (Registers 00,01)
Together these registers form a 16-bit number which linearly controls
the frequency of Oscillator 1 . The frequency is determined by the
following equation:
Fout = (Fn*Fclk/16777216) Hz
Where Fn is the 16-bit number in the Frequency registers and Fclk is
the system clock applied to the 02 input (pin 6). For a standard 1.0-MHz
clock, the frequency is given by:
Fout = (Fn*0.059604645) Hz
A complete table of values for generating 8 octaves of the equally
tempered musical scale with concert A (440 Hz) tuning is provided in
Appendix E. It should be noted that the frequency resolution of SID is
sufficient for any tuning scale and allows sweeping from note to note
(portamento) with no discernable frequency steps.
PW LO/PW HI (Registers 02,03)
Together these registers form a 12-bit number (bits 4-7 of PW HI are
not used) which linearly controls the Pulse Width (duty cycle) of the
Pulse waveform on Oscillator 1. The pulse width is determined by the
following equation:
PWout = (PWn/40.95) %
Where PWn is the 12-bit number in the Pulse Width registers.
The pulse width resolution allows the width to be smoothly swept with
no discernable stepping. Note that the Pulse waveform on Oscillator 1
must be selected in order for the Pulse Width registers to have any au-
dible effect. A value of 0 or 4095 ($FF) in the Pulse Width registers
will produce a constant DC output, while a value of 2048 ($800) will
produce a square wave.
462 APPENDIX O
~
CONTROL REGISTER (Register 04)
This register contains eight control bits which select various options
on Oscillator 1.
GATE (Bit 0): The GATE bit controls the Envelope Generator for Voice 1.
When this bit is set to a one, the Envelope Generator is Gated
(triggered) and the ATTACK/DECAY/SUSTAIN cycle is initiated. When the bit
is reset to a zero, the RELEASE cycle begins. The Envelope Generator
controls the amplitude of Oscillator I appearing at the audio output,
therefore, the GATE bit must be set (along with suitable envelope pa-
rameters) for the selected output of Oscillator 1 to be audible. A de-
tailed discussion of the Envelope Generator can be found at the end of
this Appendix.
SYNC (Bit 1): The SYNC bit, when set to a one, synchronizes the
fundamental frequency of Oscillator 1 with the fundamental frequency of
Oscillator 3, producing "Hard Sync" effects.
Varying the frequency of Oscillator 1 with respect to Oscillator 3 pro-
duces a wide range of complex harmonic structures from Voice I at the
frequency of Oscillator 3. In order for sync to occur, Oscillator 3 must
be set to some frequency other than zero but preferably lower than the
frequency of Oscillator 1. No other parameters of Voice 3 have any effect
on sync.
RING MOD (Bit 2): The RING MOD bit, when set to a one, replaces the
Triangle waveform output of Oscillator 1 with a "Ring Modulated"
combination of Oscillators 1 and 3. Varying the frequency of Oscillator 1
with respect to Oscillator 3 produces a wide range of non-harmonic
overtone structures for creating bell or gong sounds and for special ef-
fects. In order for ring modulation to be audible, the Triangle waveform
of Oscillator 1 must be selected and Oscillator 3 must be set to some
frequency other than zero. No other parameters of Voice 3 have any effect
on ring modulation.
TEST (Bit 3): The TEST bit, when set to a one, resets and locks Oscil-
lator 1 at zero until the TEST bit is cleared. The Noise waveform output
of Oscillator 1 is also reset and the Pulse waveform output is held at a
DC level. Normally this bit is used for testing purposes, however, it can
be used to synchronize Oscillator 1 to external events, allowing the
generation of highly complex waveforms under real-time software control.
APPENDIX O 463
~
(Bit 4): When set to a one, the Triangle waveform output of Oscillator
1 is selected. The Triangle waveform is low in harmonics and has a
mellow, flute-like quality.
(Bit 5): When set to a one, the Sawtooth waveform output of Oscillator
1 is selected. The Sawtooth waveform is rich in even and odd harmonics
and has a bright, brassy quality.
(Bit 6): When set to a one, the Pulse waveform output of Oscillator 1
is selected. The harmonic content of this waveform can be adjusted by the
Pulse Width registers, producing tone qualities ranging from a bright,
hollow square wave to a nasal, reedy pulse. Sweeping the pulse width in
real-time produces a dynamic "phasing" effect which adds a sense of
motion to the sound. Rapidly jumping between different pulse widths can
produce interesting harmonic sequences.
NOISE (Bit 7): When set to a one, the Noise output waveform of
Oscillator 1 is selected. This output is a random signal which changes at
the frequency of Oscillator 1. The sound quality can be varied from a low
rumbling to hissing white noise via the Oscillator 1 Frequency registers.
Noise is useful in creating explosions, gunshots, jet engines, wind, surf
and other unpitched sounds, as well as snore drums and cymbals. Sweeping
the oscillator frequency with Noise selected produces a dramatic rushing
effect.
One of the output waveforms must be selected for Oscillator 1 to be
audible, however, it is NOT necessary to de-select waveforms to silence
the output of Voice 1. The amplitude of Voice 1 at the final output is a
function of the Envelope Generator only.
+-----------------------------------------------------------------------+
| NOTE: The oscillator output waveforms are NOT additive. If more than |
| one output waveform is selected simultaneously, the result will be a |
| logical ANDing of the waveforms. Although this technique can be used |
| to generate additional waveforms beyond the four listed above, it must|
| be used with care. If any other waveform is selected while Noise is |
| on, the Noise output can "lock up " If this occurs, the Noise output |
| will remain silent until reset by the TEST bit or by bringing RES |
| (pin 5) low. |
+-----------------------------------------------------------------------+
464 APPENDIX O
~
ATTACK/DECAY (Register 05)
Bits 4-7 of this register (ATK0-ATK3) select 1 of 16 ATTACK rates for
the Voice 1 Envelope Generator. The ATTACK rate determines how rapidly
the output of Voice 1 rises from zero to peak amplitude when the Envelope
Generator is Gated. The 16 ATTACK rates are listed in Table 2.
Bits 0-3 (DCY0-DCY3) select 1 of 16 DECAY rates for the Envelope
Generator. The DECAY cycle follows the ATTACK cycle and the DECAY rate
determines how rapidly the output fails from the peak amplitude to the
selected SUSTAIN level. The 16 DECAY rates are listed in Table 2.
SUSTAIN/RELEASE (Register 06)
Bits 4-7 of this register (STN0-STN3) select 1 of 16 SUSTAIN levels for
the Envelope Generator. The SUSTAIN cycle follows the DECAY cycle and the
output of Voice 1 will remain at the selected SUSTAIN amplitude as long
as the Gate bit remains set. The SUSTAIN levels range from zero to peak
amplitude in 16 linear steps, with a SUSTAIN value of 0 selecting zero
amplitude and a SUSTAIN value of 15 ($F) selecting the peak amplitude. A
SUSTAIN value of 8 would cause Voice I to SUSTAIN at an amplitude one-
half the peak amplitude reached by the ATTACK cycle.
Bits 0-3 (RLS0-RLS3) select 1 of 16 RELEASE rates for the Envelope
Generator. The RELEASE cycle follows the SUSTAIN cycle when the Gate bit
is reset to zero. At this time, the output of Voice 1 will fall from the
SUSTAIN amplitude to zero amplitude at the selected RELEASE rate. The 16
RELEASE rates are identical to the DECAY rates.
+-----------------------------------------------------------------------+
| NOTE: The cycling of the Envelope Generator can be altered at any |
| point via the Gate bit. The Envelope Generator can be Gated and |
| Released without restriction. For example, if the Gate bit is reset |
| before the envelope has finished the ATTACK cycle, the RELEASE cycle |
| will immediately begin, starting from whatever amplitude had been |
| reached. if the envelope is then Gated again (before the RELEASE cycle|
| has reached zero amplitude), another ATTACK cycle will begin, starting|
| from whatever amplitude had been reached. This technique can be used |
| to generate complex amplitude envelopes via real-time software |
| control. |
+-----------------------------------------------------------------------+
APPENDIX O 465
~
Table 2. Envelope Rates
+-----------------+--------------------------+--------------------------+
| VALUE | ATTACK RATE | DECAY/RELEASE RATE |
+-----------------+--------------------------+--------------------------+
| DEC (HEX) | (Time/Cycle) | (Time/Cycle) |
+-----------------+--------------------------+--------------------------+
| 0 (0) | 2 ms | 6 ms |
| 1 (1) | 8 ms | 24 ms |
| 2 (2) | 16 ms | 48 ms |
| 3 (3) | 24 ms | 72 ms |
| 4 (4) | 38 ms | 114 ms |
| 5 (5) | 56 ms | 168 ms |
| 6 (6) | 68 ms | 204 ms |
| 7 (7) | 80 ms | 240 ms |
| 8 (8) | 100 ms | 300 ms |
| 9 (9) | 250 ms | 750 ms |
| 10 (A) | 500 ms | 1.5 s |
| 11 (B) | 800 ms | 2.4 s |
| 12 (C) | 1 s | 3 s |
| 13 (D) | 3 s | 9 s |
| 14 (E) | 5 s | 15 s |
| 15 (F) | 8 s | 24 s |
+-----------------+--------------------------+--------------------------+
+-----------------------------------------------------------------------+
| NOTE: Envelope rates are based on a 1.0-MHz 02 clock. For other 02 |
| frequencies, multiply the given rate by 1 MHz/02. The rates refer to |
| the amount of time per cycle. For example, given an ATTACK value of 2,|
| the ATTACK cycle would take 16 ms to rise from zero to peak amplitude.|
| The DECAY/RELEASE rates refer to the amount of time these cycles would|
| take to fall from peak amplitude to zero. |
+-----------------------------------------------------------------------+
VOICE 2
Registers 07-$0D control Voice 2 and are functionally identical to reg-
isters 00-06 with these exceptions:
1) When selected, SYNC synchronizes Oscillator 2 with Oscillator 1.
2) When selected, RING MOD replaces the Triangle output of Oscillator 2
with the ring modulated combination of Oscillators 2 and 1.
466 APPENDIX O
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VOICE 3
Registers $0E-$14 control Voice 3 and are functionally identical to
registers 00-06 with these exceptions:
1) When selected, SYNC synchronizes Oscillator 3 with Oscillator 2.
2) When selected, RING MOD replaces the Triangle output of Oscillator 3
with the ring modulated combination of Oscillators 3 and 2.
Typical operation of a voice consists of selecting the desired parame-
ters: frequency, waveform, effects (SYNC, RING MOD) and envelope rates,
then gating the voice whenever the sound is desired. The sound can be
sustained for any length of time and terminated by clearing the Gate bit.
Each voice can be used separately, with independent parameters and
gating, or in unison to create a single, powerful voice. When used in
unison, a slight detuning of each oscillator or tuning to musical
intervals creates a rich, animated sound.
FILTER
FC LO/FC HI (Registers $15,$16)
Together these registers form an 11-bit number (bits 3-7 of FC LO are
not used) which linearly controls the Cutoff (or Center) Frequency of the
programmable Filter. The approximate Cutoff Frequency ranges from 30
Hz to 12 KHz.
RES/FILT (Register $17)
Bits 4-7 of this register (RES0-RES3) control the resonance of the
filter. Resonance is a peaking effect which emphasizes frequency com-
ponents at the Cutoff Frequency of the Filter, causing a sharper sound.
There are 16 resonance settings ranging linearly from no resonance (0) to
maximum resonance (15 or $F). Bits 0-3 determine which signals will be
routed through the Filter:
FILT 1 (Bit 0): When set to a zero, Voice 1 appears directly at the
audio output and the Filter has no effect on it. When set to a one, Voice
1 will be processed through the Filter and the harmonic content of Voice
1 will be altered according to the selected Filter parameters.
FILT 2 (Bit 1): Same as bit 0 for Voice 2.
FILT 3 (Bit 2): Same as bit 0 for Voice 3.
FILTEX (Bit 3): Same as bit 0 for External audio input (pin 26).
APPENDIX O 467
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MODE/VOL (Register $18)
Bits 4-7 of this register select various Filter mode and output
options:
LP (Bit 4): When set to a one, the Low-Pass output of the Filter is
selected and sent to the audio output. For a given Filter input signal,
all frequency components below the Filter Cutoff Frequency are passed
unaltered, while all frequency components above the Cutoff are attenuated
at a rate of 12 dB/Octave. The Low-Pass mode produces fullbodied sounds.
BP (Bit 5): Same as bit 4 for the Bandpass output. All frequency
components above and below the Cutoff are attenuated at a rate of 6
dB/Octave. The Bandpass mode produces thin, open sounds.
HP (Bit 6): Same as bit 4 for the High-Pass output. All frequency
components above the Cutoff are passed unaltered, while all frequency
components below the Cutoff are attenuated at a rate of 12 dB/Octave.
The High-Pass mode produces tinny, buzzy sounds.
3 OFF (Bit 7): When set to a one, the output of Voice 3 is disconnected
from the direct audio path. Setting Voice 3 to bypass the Filter
(FILT 3 = 0) and setting 3 OFF to a one prevents Voice 3 from reaching
the audio output. This allows Voice 3 to be used for modulation purposes
without any undesirable output.
+-----------------------------------------------------------------------+
| NOTE: The Filter output modes ARE additive and multiple Filter modes |
| may be selected simultaneously. For example, both LP and HP modes can |
| be selected to produce a Notch (or Band Reject) Filter response. In |
| order for the Filter to have any audible effect, at least one Filter |
| output must be selected and at least one Voice must be routed through |
| the Filter. The Filter is, perhaps, the most important element in SID |
| as it allows the generation of complex tone colors via subtractive |
| synthesis (the Filter is used to eliminate specific frequency |
| components from a harmonically rich input signal). The best results |
| are achieved by varying the Cutoff Frequency in real-time. |
+-----------------------------------------------------------------------+
Bits 0-3 (VOL0-VOL3) select 1 of 16 overall Volume levels for the final
composite audio output. The output volume levels range from no output (0)
to maximum volume (15 or $F) in 16 linear steps. This control can be used
as a static volume control for balancing levels in multi-chip systems or
for creating dynamic volume effects, such as Tremolo. Some Volume level
other than zero must be selected in order for SID to produce any sound.
468 APPENDIX O
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MISCELLANEOUS
POTX (Register $19)
This register allows the microprocessor to read the position of the
potentiometer tied to POTX (pin 24), with values ranging from 0 at
minimum resistance, to 255 ($FF) at maximum resistance. The value is
always valid and is updated every 512 (02 clock cycles. See the Pin
Description section for information on pot and capacitor values.
POTY (Register $1A)
Same as POTX for the pot tied to POTY (pin 23).
OSC 3/RANDOM (Register $1B)
This register allows the microprocessor to read the upper 8 output bits
of Oscillator 3. The character of the numbers generated is directly re-
lated to the waveform selected. If the Sawtooth waveform of Oscillator 3
is selected, this register will present a series of numbers incrementing
from 0 to 255 ($FF) at a rate determined by the frequency of Oscillator
3. If the Triangle waveform is selected, the output will increment from 0
up to 255, then decrement down to 0. If the Pulse waveform is selected,
the output will jump between 0 and 255. Selecting the Noise waveform
will produce a series of random numbers, therefore, this register can be
used as a random number generator for games. There are numerous timing
and sequencing applications for the OSC 3 register, however, the chief
function is probably that of a modulation generator. The numbers
generated by this register can be added, via software, to the Oscillator
or Filter Frequency registers or the Pulse Width registers in real-time.
Many dynamic effects can be generated in this manner. Siren-like sounds
can be created by adding the OSC 3 Sawtooth output to the frequency
control of another oscillator. Synthesizer "Sample and Hold" effects can
be produced by adding the OSC 3 Noise output to the Filter Frequency
control registers. Vibrato can be produced by setting Oscillator 3 to a
frequency around 7 Hz and adding the OSC 3 Triangle output (with proper
scaling) to the Frequency control of another oscillator. An unlimited
range of effects are available by altering the frequency of Oscillator 3
and scaling the OSC 3 output. Normally, when Oscillator 3 is used for
modulation, the audio output of Voice 3 should be eliminated (3 OFF = 1).
APPENDIX O 469
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ENV 3 (Register $1C)
Same as OSC 3, but this register allows the microprocessor to read the
output of the Voice 3 Envelope Generator. This output can be added to the
Filter Frequency to produce harmonic envelopes, WAH-WAH, and similar
effects. "Phaser" sounds can be created by adding this output to the
frequency control registers of an oscillator. The Voice 3 Envelope
Generator must be Gated in order to produce any output from this regis-
ter. The OSC 3 register, however, always reflects the changing output of
the oscillator and is not affected in any way by the Envelope Generator.
SID PIN DESCRIPTION
CAP1A,CAP1B, (Pins 1,2)/ CAP2A,CAP2B (Pins 3,4)
These pins are used to connect the two integrating capacitors required
by the programmable Filter. C1 connects between pins 1 and 2, C2 between
pins 3 and 4. Both capacitors should be the some value. Normal operation
of the Filter over the audio range (approximately 30 Hz-12 kHz) is
accomplished with a value of 2200 pF for C1 and C2. Polystyrene
capacitors are preferred and in complex polyphonic systems, where many
SID chips must track each other, matched capacitors are recommended.
The frequency range of the Filter can be tailored to specific applica-
tions by the choice of capacitor values. For example, a low-cost game may
not require full high-frequency response. In this case, larger values
for C1 and C2 could be chosen to provide more control over the bass
frequencies of the Filter. The maximum Cutoff Frequency of the Filter is
given by:
FCmax = 2.6E-5/C
Where C is the capacitor value. The range of the Filter extends 9 octaves
below the maximum Cutoff Frequency.
RES (Pin 5)
This TTL-level input is the reset control for SID. When brought low for
at least ten 02 cycles, all internal registers are reset to zero and the
audio output is silenced. This pin is normally connected to the reset
line of the microprocessor or a power-on-clear circuit.
470 APPENDIX O
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02 (Pin 6)
This TTL-Level input is the master clock for SID. All oscillator
frequencies and envelope rates are referenced to this clock. 02 also
controls data transfers between SID and the microprocessor. Data can only
be transferred when (02 is high. Essentially, (02 acts as a high-active
chip select as far as data transfers are concerned. This pin is normally
connected to the system clock, with a nominal operating frequency of 1.0
MHz.
R/W (Pin 7)
This TTL-level input controls the direction of data transfers between
SID and the microprocessor. If the chip select conditions have been met,
a high on this line allows the microprocessor to Read data from the
selected SID register and a low allows the microprocessor to Write data
into the selected SID register. This pin is normally connected to the
system Read/Write line.
CS (Pin 8)
This TTL-Level input is a low active chip select which controls data
transfers between SID and the microprocessor. CS must be low for any
transfer. A Read from the selected SID register can only occur if CS is
low, 02 is high and R/W is high. A Write to the selected SID register can
only occur if CS is low, (02 is high and R/W is low. This pin is normally
connected to address decoding circuitry, allowing SID to reside in the
memory map of a system.
A0-A4 (Pins 9-13)
These TTL-Level inputs are used to select one of the 29 SID registers.
Although enough addresses are provided to select 1 of 32 registers, the
remaining three register locations are not used. A Write to any of these
three locations is ignored and a Read returns invalid data. These pins
are normally connected to the corresponding address lines of the micro-
processor so that SID may be addressed in the same manner as memory.
GND (Pin 14)
For best results, the ground line between SID and the power supply
should be separate from ground lines to other digital circuitry. This
will minimize digital noise at the audio output.
APPENDIX O 471
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D0-D7 (Pins 15-22)
These bidirectional lines are used to transfer data between SID and the
microprocessor. They are TTL compatible in the input mode and capable of
driving 2 TTL loads in the output mode. The data buffers are usually in
the high-impedance off state. During a Write operation, the data buffers
remain in the off (input) state and the microprocessor supplies data to
SID over these lines. During a Read operation, the data buffers turn on
and SID supplies data to the microprocessor over these lines. The pins
are normally connected to the corresponding data lines of the micro-
processor.
POTX,POTY (Pins 24,23)
These pins are inputs to the A/D converters used to digitize the posi-
tion of potentiometers. The conversion process is based on the time con-
stant of a capacitor tied from the POT pin to ground, charged by a
potentiometer tied from the POT pin to +5 volts. The component values are
determined by:
RC = 4.7E-4
Where R is the maximum resistance of the pot and C is the capacitor.
The larger the capacitor, the smaller the POT value jitter. The recom-
mended values for R and C are 470 komhs and 1000 pF. Note that a separate
pot and cap are required for each POT pin.
VCC (Pin 25)
As with the GND line, a separate +5 VDC line should be run between SID
Vcc and the power supply in order to minimize noise. A bypass capacitor
should be located close to the pin.
EXT IN (Pin 26)
This analog input allows external audio signals to be mixed with the
audio output of SID or processed through the Filter. Typical sources in-
clude voice, guitar, and organ. The input impedance of this pin is on the
order of 100 kohms. Any signal applied directly to the pin should ride at
a DC level of 6 volts and should not exceed 3 volts p-p. In order to pre-
472 APPENDIX O
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vent any interference caused by DC level differences, external signals
should be AC-coupled to EXT IN by an electrolytic capacitor in the 1-10
uF range. As the direct audio path (FILTEX=0) has unity gain, EXT IN can
be used to mix outputs of many SID chips by daisy-chaining. The number of
chips that can be chained in this manner is determined by the amount of
noise and distortion allowable at the final output. Note that the output
Volume control will affect not only the three SID voices, but also any
external inputs.
AUDIO OUT (Pin 27)
This open-source buffer is the final audio output of SID, comprised of
the three SID voices, the Filter and any external input. The output level
is set by the output Volume control and reaches a maximum of 2 volts p-p
at a DC level of 6 volts. A source resistor from AUDIO OUT to ground is
required for proper operation. The recommended resistance is 1 kohm for
a standard output impedance.
As the output of SID rides at a 6-volt DC level, it should be AC-
coupled to any audio amplifier with an electrolytic capacitor in the 1-10
uF range.
VDD (Pin 28)
As with Vcc, a separate +12 VDC line should be run to SID VDD and a
bypass capacitor should be used.
6581 SID CHARACTERISTICS
ABSOLUTE MAXIMUM RATINGS
+--------------------------+------------+-----------------+-------------+
| RATING | SYMBOL | VALUE | UNITS |
+--------------------------+------------+-----------------+-------------+
| Supply Voltage | VDD | -0.3 to +17 | VDC |
| Supply Voltage | VCC | -0.3 to +7 | VDC |
| Input Voltage (analog) | Vina | -0.3 to +17 | VDC |
| Input Voltage (digital) | Vind | -0.3 to +7 | VDC |
| Operating Temperature | Ta | 0 to +70 | Celsius |
| Storage Temperature | Tstg | -55 to +150 | Celsius |
+--------------------------+------------+-----------------+-------------+
APPENDIX O 473
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ELECTRICAL CHARACTERISTICS (Vdd=12 VDC+-5%, Vcc=5 VDC+-5%,
Ta=0 to 70 Celsius)
+------------------------------------------+----+-----+---+-------+-----+
| CHARACTERISTIC SYMBOL MIN |TYP| MAX |UNITS|
+------------------------------------------+----+-----+---+-------+-----+
| Input High Voltage (RES, 02, RIN, CS, | Vih| 2 | - | Vcc | VDC |
| Input Low Voltage A0-A4, D0-D7) | Vil|-0.3 | - | 0.8 | VDC |
+------------------------------------------+----+-----+---+-------+-----+
| Input Leakage Current (RES, 02, R/W, CS, | Iin| - | - | 2.5 | uA |
| A0-A4; Vin=0-5 VDC)| | | | | |
| Three-State (Off) (D0-D7; Vcc=max) |Itsi| - | - | 10 | uA |
+------------------------------------------+----+-----+---+-------+-----+
| Input Leakage Current Vin=0.4-2.4 VDC | | | | | |
+------------------------------------------+----+-----+---+-------+-----+
| Output High Voltage (D0-D7; Vcc=min, | Voh| 2.4 | - |Vcc-0.7| VDC |
| I load=200 uA) | | | | | |
+------------------------------------------+----+-----+---+-------+-----+
| Output Low Voltage (D0-D7; Vcc=max, | Vol| GND | - | 0.4 | VDC |
| I load=3.2 mA) | | | | | |
+------------------------------------------+----+-----+---+-------+-----+
| Output High Current (D0-D7; Sourcing, | Ioh| 200 | - | - | uA |
| Voh=2.4 VDC) | | | | | |
+------------------------------------------+----+-----+---+-------+-----+
| Output Low Current (D0-D7; Sinking, | Iol| 3.2 | - | - | mA |
| Vol=0.4 VDC) | | | | | |
+------------------------------------------+----+-----+---+-------+-----+
| Input Capacitance (RES, 02, R/W, CS, | Cin| - | - | 10 | pF |
| A0-A4, D0-D7) | | | | | |
+------------------------------------------+----+-----+---+-------+-----+
| Pot Trigger Voltage (POTX, POTY) |Vpot| - Vcc/2 - | VDC |
+------------------------------------------+----+-----+---+-------+-----+
| Pot Sink Current (POTX, POTY) |Ipot| 500 | - | - | uA |
+------------------------------------------+----+-----+---+-------+-----+
| Input Impedance (EXT IN) | Rin| 100 |150| - |kohms|
+------------------------------------------+----+-----+---+-------+-----+
| Audio Input Voltage (EXT IN) | Vin| 5.7 | 6 | 6.3 | VDC |
| | | - |0.5| 3 | VAC |
474 APPENDIX O
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+------------------------------------------+----+-----+---+-------+-----+
| Audio Output Voltage (AUDIO OUT; 1 kohm | | | | | |
| load, volume=max) |Vout| 5.7 | 6 | 6.3 | VDC |
| One Voice on: | | 0.4 |0.5| 0.6 | VAC |
| All Voices on: | | 1.0 |1.5| 2.0 | VAC |
+------------------------------------------+----+-----+---+-------+-----+
| Power Supply Current (VDD) | Idd| - | 20| 25 | mA |
+------------------------------------------+----+-----+---+-------+-----+
| Power Supply Current (VCC) | Icc| - | 70| 100 | mA |
+------------------------------------------+----+-----+---+-------+-----+
| Power Dissipation (Total) | Pd | - |600| 1000 | mW |
+------------------------------------------+----+-----+---+-------+-----+
APPENDIX O 475
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6581 SID TIMING
[THE PICTURE IS MISSING!]
READ CYCLE
+----------+----------------------------+-------+-------+-------+-------+
| SYMBOL | NAME | MIN | TYP | MAX | UNITS |
+----------+----------------------------+-------+-------+-------+-------+
| Tcyc | Clock Cycle Time | 1 | - | 20 | uA |
| Tc | Clock High Pulse Width | 450 | 500 |10,000 | ns |
| Tr,Tf | Clock Rise/Fall Time | - | - | 25 | ns |
| Trs | Read Set-Up Time | 0 | - | - | ns |
| Trh | Read Hold Time | 0 | - | - | ns |
| Tacc | Access Time | - | - | 300 | ns |
| Tah | Address Hold Time | 10 | - | - | ns |
| Tch | Chip Select Hold Time | 0 | - | - | ns |
| Tdh | Data Hold Time | 20 | - | - | ns |
+----------+----------------------------+-------+-------+-------+-------+
476 APPENDIX O
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[THE PICTURE IS MISSING!]
WRITE CYCLE
+----------+----------------------------+-------+-------+-------+-------+
| SYMBOL | NAME | MIN | TYP | MAX | UNITS |
+----------+----------------------------+-------+-------+-------+-------+
| Tw | Write Pulse Width | 300 | - | - | ns |
| Twh | Write Hold Time | 0 | - | - | ns |
| Taws | Address Set-up Time | 0 | - | - | ns |
| Tah | Address Hold Time | 10 | - | - | ns |
| Tch | Chip Select Hold Time | 0 | - | - | ns |
| Tvd | Valid Data | 80 | - | - | ns |
| Tdh | Data Hold Time | 10 | - | - | ns |
+----------+----------------------------+-------+-------+-------+-------+
APPENDIX O 477
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EQUAL-TEMPERED MUSICAL SCALE VALUES
The table in Appendix E lists the numerical values which must be stored
in the SID Oscillator frequency control registers to produce the notes of
the equal-tempered musical scale. The equal-tempered scale consists of an
octave containing 12 semitones (notes): C,D,E,F,G,A,B and C#,D#,F#,G#,A#.
The frequency of each semitone is exactly the 12th root of 2 times the
frequency of the previous semitone. The table is based on a (02 clock of
1.02 MHz. Refer to the equation given in the Register Description for use
of other master clock frequencies. The scale selected is concert pitch,
in which A-4 = 440 Hz. Transpositions of this scale and scales other than
the equal-tempered scale are also possible.
Although the table in Appendix E provides a simple and quick method for
generating the equal-tempered scale, it is very memory inefficient as it
requires 192 bytes for the table alone. Memory efficiency can be improved
by determining the note value algorithmically. Using the fact that each
note in an octave is exactly half the frequency of that note in the next
octave, the note look-up table can be reduced from 96 entries to 12
entries, as there are 12 notes per octave. If the 12 entries (24 bytes)
consist of the 16-bit values for the eighth octave (C-7 through B-7),
then notes in lower octaves can be derived by choosing the appropriate
note in the eighth octave and dividing the 16-bit value by two for each
octave of difference. As division by two is nothing more than a right-
shift of the value, the calculation can easily be accomplished by a
simple software routine. Although note B-7 is beyond the range of the
oscillators, this value should still be included in the table for
calculation purposes (the MSB of B-7 would require a special software
case, such as generating this bit in the CARRY before shifting). Each
note must be specified in a form which indicates which of the 12
semitones is desired, and which of the eight octaves the semitone is in.
Since four bits are necessary to select 1 of 12 semitones and three bits
are necessary to select 1 of 8 octaves, the information can fit in one
byte, with the lower nybble selecting the semitone (by addressing the
look-up table) and the upper nybble being used by the division routine to
determine how many times the table value must be right-shifted.
478 APPENDIX O
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SID ENVELOPE GENERATORS
The four-part ADSR (ATTACK, DECAY, SUSTAIN, RELEASE) envelope generator
has been proven in electronic music to provide the optimum trade-off
between flexibility and ease of amplitude control. Appropriate selection
of envelope parameters allows the simulation of a wide range 2: of
percussion and sustained instruments. The violin is a good example of a
sustained instrument. The violinist controls the volume by bowing the
instrument. Typically, the volume builds slowly, reaches a peak, then
drops to an intermediate level. The violinist can maintain this level for
as long as desired, then the volume is allowed to slowly die away. A
"snapshot" of this envelope is shown below:
PEAK AMPLITUDE --- + <- SUSTAIN ->
/ \ PERIOD
A/ D\ S R
/ +------------+
/ INTERMEDIATE +
/ LEVEL +
ZERO AMPLITUDE ---+ +--
This volume envelope can be easily reproduced by the ADSR as shown
below, with typical envelope rates:
+
/ \
/ +--------+
ATTACK: 10 ($A) 500 ms / +
DECAY: 8 300 ms --+ A D S R +-
SUSTAIN: 10 ($A)
RELEASE: 9 750 ms
GATE+--------------+
--+ +-----
Note that the tone can be held at the intermediate SUSTAIN level for
as long as desired. The tone will not begin to die away until GATE is
cleared. With minor alterations, this basic envelope can be used for
brass and woodwinds as well as strings.
An entirely different form of envelope is produced by percussion in-
struments such as drums, cymbals and gongs, as well as certain
keyboards such as pianos and harpsichords. The percussion envelope is
characterized by a nearly instantaneous attack, immediately followed by
a decay to zero volume. Percussion instruments cannot be sustained at
APPENDIX O 479
~
a constant amplitude. For example, the instant a drum is struck, the
sound reaches full volume and decays rapidly regardless of how it was
struck. A typical cymbal envelope is shown below:
ATTACK: 0 2 ms +
DECAY: 9 750 ms |+
SUSTAIN: 0 | +
RELEASE: 9 750 ms ----+ +--
A D
Note that the tone immediately begins to decay to zero amplitude after
the peak is reached, regardless of when GATE is cleared. The amplitude
envelope of pianos and harpsichords is somewhat more complicated, but can
be generated quite easily with the ADSR. These instruments reach full
volume when a key is first struck. The amplitude immediately begins to
die away slowly as long as the key remains depressed. If the key is
released before the sound has fully died away, the amplitude will
immediately drop to zero. This envelope is shown below:
ATTACK: 0 2 ms +
DECAY: 9 750 ms |+
SUSTAIN: 0 | +
RELEASE: 0 6 ms ----+ +-----
A D R
Note that the tone decays slowly until GATE is cleared, at which point
the amplitude drops rapidly to zero.
The most simple envelope is that of the organ, When a key is pressed,
the tone immediately reaches full volume and remains there. When the key
is released, the tone drops immediately to zero volume. This envelope is
shown below:
+----+
ATTACK: 0 2 ms | |
DECAY: 0 6 ms | |
SUSTAIN: 15 ($F) | |
RELEASE: 0 6 ms ----+ +---
A S R
The real power of SID lies in the ability to create original sounds
rather than simulations of acoustic instruments. The ADSR is capable of
creating envelopes which do not correspond to any "real" instruments. A
good example would be the "backwards" envelope. This envelope is
characterized by a slow attack and rapid decay which sounds very much
480 APPENDIX O
~
like an instrument that has been recorded on tape then played backwards.
This envelope is shown below: S
+----------+
ATTACK: 10 ($A) 500 ms A / | R
DECAY: 0 6 ms / +
SUSTAIN: 15 ($F) / +
RELEASE: 3 72 ms --+ +--
Many unique sounds can be created by applying the amplitude envelope of
one instrument to the harmonic structure of another. This produces sounds
similar to familiar acoustic instruments, yet notably different. In
general, sound is quite subjective and experimentation with various
envelope rates and harmonic contents will be necessary in order to
achieve the desired sound.
[THE PICTURE IS MISSING!]
TYPICAL 6581/SID APPLICATION
APPENDIX O 481
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APPENDIX P
GLOSSARY
ADSR Attack/Decay/Sustain/Release envelope.
attack Rate at which musical note reaches peak volume.
binary Base-2 number system.
Boolean operators Logical operators.
byte Memory location.
CHROMA noise Color distortion.
CIA Complex Interface Adapter.
DDR Data Direction Register.
decay Rate at which musical note falls from peak
volume to sustain volume.
decimal Base-10 number system.
e Mathematical constant (approx. 2.71828183).
envelope Shape of the volume of a note over time.
FIFO First-In/First-Out.
hexadecimal Base-16 number system.
integer Whole number (without decimal point).
jiffy clock Hardware interval timer.
NMI Non-Maskable Interrupt.
octal Base-8 number system.
operand Parameter.
OS Operating System.
pixel Dot of resolution on the screen.
queue Single-file line.
register Special memory storage location.
release Rate at which a musical note fails from
sustain volume to no volume.
ROM Read-Only Memory.
SID Sound Interface Device
signed numbers Plus or minus numbers.
subscript Index variable.
sustain Volume level for sustain of musical note.
syntax Programming sentence structure.
truncated Cut off, eliminated (not rounded).
VIC-II Video Interface Chip.
video screen Television set
482 APPENDIX P
~
INDEX
Abbreviations, BASIC Commands, Statements, and Functions, x, 29, 31-34,
374-375
ABS function, 31, 35, 374
Accessories, 335-371
Accumulator, 213
ACPTR, 272-274
ADC, 232, 235, 254
Addition, 3, 9-11, 16
Addressing, 211, 215-217, 411-413
A/D/S/R, 183-185, 189, 196-199
AND, 232, 235, 254
AND operator, 13-16, 31, 35-36, 374
Animation, xiii, 153, 166
Applications, xiii-xvi
Arithmetic expressions, 10-12
Arithmetic operators, 10-12, 16
Arrays, 10-12, 44-45
ASC function, 31, 37, 374
ASCII character codes, 31, 38, 340, 374
ASL, 232, 236, 254
Assembler, 215, 218, 227, 310
ArcTaNgent function, 31, 38, 374
Attack, (see A/D/S/R)
Bank selection, 101-102, 133
BASIC abbreviations, 29, 31-34, 374-375
BASIC commands, 31-34, 41, 58-60, 62, 81-82, 91
BASIC miscellaneous functions, 31-34, 43-44, 49, 56-57, 61, 69, 70, 80,
83-85, 89
BASIC numeric functions, 31-35, 37-38, 42, 46-47, 49, 83-84, 88-89
BASIC operators, 3, 9-15, 31-36, 63-64, 68, 92
BASIC statements, 18-26, 31-34, 39-55, 57, 62-67, 69-79, 86-87, 92
BASIC string functions, 31-34, 38, 56, 61, 79, 87, 89
BASIC variables, 7-26
BCC, 232, 236, 254
BCS, 232, 236, 254
BEQ, 226-227, 232, 237, 254
Bibliography, 388-390
Binary, 69, 92, 108, 112, 216-217
Bit, 99-149, 290, 298, 300-301, 305, 343-357, 359
INDEX 483
~
BIT, 232, 237, 254
Bit map mode, 121-130
Bit map mode, multicolor, 127-130
Bit mapping, 121-130
BMI, 232, 237, 254
BNE, 226-227, 232, 238, 254
Boolean arithmetic, 14
BPL, 232, 238, 254
Branches and testing, 226-227
BRK, 232, 238, 254
Buffer, keyboard, 93
Business aids, xiii-xvi
BVC, 232, 239, 254
BVS, 232, 239, 254
Byte, 9, 104, 108, 117-119, 124-127, 196, 213, 218-220, 222-227, 260-263,
274, 278-279, 286, 292-293, 299, 307, 349, 357-359
Cassette port, 337, 340-342
Cassette, tape recorder, xiii, 39-41, 65-67, 81-82, 91, 187, 192, 283,
293-294, 297, 320-321, 337-338, 340-342
Character PEEKs and POKES, 104, 106, 109-111, 115, 118, 120-122, 127-130,
134-137, 150, 154-155, 159-161, 165-166
CHAREN, 260-261
CHKIN, 272-273, 275
CHKOUT, 272-273, 276
CHRGET, 272-273, 307-308
CHRIN, 272-273, 277-278
CHROUT, 272-273, 278-279
CHR$ function, 24, 31, 37-38, 45, 50, 55, 75-76, 93-94, 97, 120, 156,
336-342, 374, 379-381
CINT, 272-273, 280
CIOUT, 272-273, 279-280
CLALL, 272-273, 281
CLC, 232, 239, 254
CLD, 232, 240, 254
CLI, 232, 240, 254
Clock, 80, 89, 314, 329-332, 366, 406-408, 421-427, 431, 451
Clock timing diagram, 406-408
CLOSE, 272-273, 281-282
CLOSE statement, 31, 39-41, 348, 354, 374
CLR statement, 31, 39-40, 81, 109, 374
CLRCHN, 272-273, 282
484 INDEX
~
CLR/HOME key, 220
CLV, 232, 240, 254
CMD statement, 31, 40-41, 374
CMP, 232, 241, 254
Collision detect, 144-145, 180
Color adjustment, 113
Color combinations chart, 152
Color memory, 103
Color register, 117, 120, 128, 135-136, 179
Color screen, background, border, 115-119, 128, 135-137, 176, 179-180
Commands, BASIC, 31-92
Commodore magazine, xvii-xviii, 390
Commodore 64 memory map, 310
Complement, twos, 63-64
Constants, floating-point, integer, string, 4-7, 46, 77-78
CONTinue command, 31, 41-42, 46, 81, 86, 374
ConTRoL key, 58, 72, 93-97, 171
COSine function, 31-34, 42, 374
CP/M, x, xiv, 368-371
CPX, 227, 232, 241, 254
CPY, 227, 232, 241, 254
Crunching BASIC programs, 24-27, 156
CuRSoR keys, 93-97, 336
DATASSETTE(TM) recorder, (see cassette, tape recorder)
DATA statement, 26, 31, 42-43, 76-77, 111-114, 164, 169, 174, 374
DEC, 232, 242, 254
Decay, (see AIDIS/R)
DEFine FuNction statement, 31, 43-44, 374
DELete key, 71-72, 95-96
DEX, 226, 232 242, 254
DEY, 226, 232: 242, 254
DiMension statement, 9, 31, 44-45, 374
Direct mode, 3
Division, 3, 10-11
Edit mode, 93-97
Editor, screen, 93-97
END statement, 32, 46, 79, 93, 374
Envelope generator, (see A/D/S/R)
EOR, 232, 243, 254
Equal, not-equal-to signs, 3, 9-12
INDEX 485
~
Error messages, 306, 400-401
Expansion port(s), (also user port, serial port, RS-232 port), 335-371
EXPonent function, 32, 46, 374
Exponentiation, 5-6, 10, 12, 16
Files (cassette), 40, 50, 55, 59-60, 65-66, 75, 84-85, 91, 337-338,
340-342
Files (disk), 40, 50, 55, 59-60, 65-66, 75, 84-85, 91, 337-338, 342
Filtering, 183, 189, 199-202
Fire button, joystick/paddle/lightpen, 328-329, 343-348
FOR statement, 20-21, 32, 39, 47-48, 62-63, 77-78, 86, 110, 155-156,
165-166, 169-171, 198-199, 309, 374
Football, 45
FREE function, 32, 49, 109, 374
FuNction function, 32, 47, 374
Functions, 31-34, 35, 37-38, 42, 46-47, 49, 56-57, 61, 69-70, 79-80,
83-85, 87-90, 374-375
Game controls and ports, 343-348
GET statement, 22-24, 32, 37, 49-50, 93, 374-375
GETIN, 272-273, 283
GET# statement, 32, 37, 50, 55, 65, 341-342, 348, 374
GOSUB statement, 32, 39, 51-52, 77, 79, 85, 374
GOTO (GO TO) statement, 32, 37, 48, 52-53, 64, 77, 81, 86, 374
Graphics keys, xiv-xv, 70-74, 95-96, 108-114
Graphics mode, xiv-xv, 99-183
Graphics mode, bit mapped, 121-130
Graphics symbols, (see graphics keys)
Greater than, equal to or, 3, 12-13, 16
Hexadecimal notation, 101, 209, 215-218
Hierarchy of operations, 16
IEEE-488 interface, (see serial port)
IF...THEN statement, 32, 46-47, 49, 52-53, 64, 70, 86, 172-173, 180, 374
INC, 232, 243, 254
Income/expense program, 20-21
Indexed indirect, 224-225
Indexing, 223-225
Indirect indexed, 223-224
INPUT statement, 18-22, 32, 45, 53-55, 93, 374
INPUT# statement, 32, 55, 75, 86, 88, 90, 374
INSerT key, 72, 95-96
486 INDEX
~
INTeger function, 32, 56, 80, 374
Integer,, arrays, constants, variables, 4-5, 7-9
INX, 226-227, 232, 243, 254
INY, 226-227, 232, 244, 254
IOBASE, 272-273, 284
I/O Guide, 335-375
IOINIT, 272-273, 285
I/O Pinouts, 395-397
I/O Ports, 214, 260, 335-375
I/O Registers, 104-106, 212-214
I/O Statements, 39, 50, 54-55, 65-67, 75
IRQ, 308
Joysticks, 343-345
JMP, 228-230, 232, 244, 254, 270, 308
JSR, 228-230, 233, 244, 255, 268, 270
KERNAL, 2, 94, 209, 228-230, 308, 268-306, 348-358
Keyboard, 93-98
Keywords, BASIC, 29-92
LDA, 218-220, 233, 245, 255
LDX, 233, 245, 255
LDY, 233, 246, 255
LEFT$ function, 32, 56, 375
LENgth function, 32, 57, 375
Less than, equal to or, 3, 12-13, 16
LET statement, 32, 57, 375
LIST command, 32, 58, 375
LISTEN, 272-273, 285
LOAD, 272-273, 286
LOAD command, 32, 59-60, 370, 375
Loading programs from tape, disk, 59-60, 337-338, 340-342
LOGarithm function, 32, 61, 375
Lower case characters, 72-74, 105
LPX (LPY), 348
LSR, 233, 246, 255
Machine language, 209-334, 411-413
Mask, 92
Mathematics formulas, 394
Mathematical symbols, 3, 6-17, 394
INDEX 487
~
MEMBOT, 272-273, 287
Memory maps, 212, 262-267, 272-273,
310-3@4
Memory map, abbreviated, 212
Memory reallocation, 101-103
MEMTOP, 272-273, 288
MID$ function, 33, 61, 375
Modem, xiii-xviii, 339-340
Modulation, 183, 207-208
Multiplication, 3, 10-11
Music, 183-208
NEW command, 18, 33, 62, 111, 117, 185, 187,375
NEXT command, 20-21, 33, 39, 47-48, 62-63, 77-78, 86, 110, 155-156,
165-166, 169-171, 198-199, 309, 375
NOP, 233, 246, 255
NOT operator, 13-16, 33, 63-64, 375
Note types, 190
Numeric variables, 7-8, 26
ON (ON...GOTO/GOSUB) statement, 33, 64,375
OPEN, 272-273, 289
OPEN statement, 33, 41, 65-67, 75-76, 85, 94, 337-339, 349-352, 375
Operating system, 210-211
Operators, arithmetic, 3, 9-12, 16
Operators, logical, 13-16, 31-33, 35-37, 63-64, 68, 374-375
Operators, relational, 3, 10-12, 16
OR operator, 13-26, 33, 68, 101-102, 104, 106, 115, 118, 120, 122,
126-127, 129, 134, 136-137, 375
ORA, 233, 247, 255
Parentheses, 3, 8, 30, 33, 83-84, 88, 375
PEEK function, 33, 69, 93, 101-102, 104, 106, 108-111, 115, 118, 120-122,
126-130, 134-137, 145, 150, 159-160, 176-177, 180, 185, 211, 361, 375
Peripherals, (see I/O Guide)
PHA, 233, 247, 255
PHP, 233, 247, 255
Pinouts, (also see I/O Pinouts), 363, 395-397
PLA, 233, 248, 255
PLOT, 273, 290
PLP, 233, 248, 255
488 INDEX
~
POKE statement, 25, 33, 69-70, 94, 101-102, 104, 106, 109-111, 115-116,
118, 120-123, 126-130, 134-137, 150, 153-161, 165-166, 168-170,
172-173, 177-178, 180, 184-186, 194, 198-199, 204-205, 211, 220, 309,
361, 375-376
Ports, I/O, 214, 335-375, 395-397
POSition function, 33, 70, 375
Power/Play, xvi, 390
PRINT statement, 13-15, 18-22, 25, 33-54, 56-61, 63, 68-75, 79-80,
83-84, 87-89, 94-96, 109, 168, 171, 210, 213, 220, 375
PRINT# statement, 33, 40-41, 75-76, 85, 94, 337, 340-341, 348, 353, 375
Printer, xv, 338-339
Program counter, 214
Program mode, 3
Prompt, 45
Quotation marks, xi, 3, 23, 72, 95, 337
Quote mode, 72-73, 95-96
RAM, 49, 100-101, 104-105, 107-108, 110-111, 117, 122, 260-262, 269, 340
RAMTAS, 273, 291
Random numbers, 53, 80
RaNDom function, 33, 43, 53, 80, 375
Raster interrupt, 131, 150-152
RDTIM, 273, 291
READST, 273, 292
READ statement, 33, 42, 76-77, 111, 170, 309,375
Release, (see A/D/S/R)
Register map, CIA chip, 428
Register map, SID chip, 461
Register map, VIC chip, 454-455
REMark statement, 25-26, 33, 37-38, 41-42, 45-46, 50, 77-78, 93-95, 101,
118, 198-199, 338, 340, 356, 375
Reserved words, (see Keywords, BASIC)
RESTOR, 273, 293
RESTORE key, 22, 92, 126, 353
RESTORE statement, 33, 78, 375
RETURN key, 3, 18, 22, 41, 50-51, 74, 93-97, 154-155, 166, 217, 220,
336-337, 370
RETURN statement, 33, 51-52, 79, 85, 175, 375
ReVerSe ON, OFF keys, 97
RIGHT$ function, 33, 79, 375
ROL, 233, 248, 255
ROM, 261, 268-269
INDEX 489
~
ROM, character generator, 103-111, 134
ROR, 233, 249, 255
RS-232C, 335, 348-359
RTI, 233, 249, 255, 308
RTS, 233, 249, 255
RUN command, 33, 40, 59, 81, 113, 154, 375
RUN/STOP key, 22, 41-42, 52, 58, 86, 92, 126, 220, 353
SAVE, 273, 293-294
SAVE command, 34, 81-82, 375
SBC, 233, 250, 255
SCNKEY, 273, 295
SCREEN, 273, 295-296
Screen editor, 2, 94-97, 211
Screen memory, 102-103
Scrolling, 128-130, 166
SEC, 233, 250, 255
SECOND, 273, 296
SED, 233, 250, 255
SEI, 233, 251, 255
Serial port (IEEE-488), 262, 331, 333, 362-366, 432-433
SETLFS, 273, 297
SETMSG, 273, 298
SETNAM, 273, 299
SETTIM, 273, 299-300
SETTMO, 273, 300-301
SGN function, 34, 83, 109, 375
SHIFT key, 4, 30, 72, 74, 94, 96-97, 168, 220
SID chip programming, xiv, 183-208
SID chip specifications, 457-481
SID chip memory map, 223-328
SiNe function, 34, 83, 375
Sound waves, 186-187, 192-196
SPaCe function, 27, 34, 83-84, 336, 375
Sprites, x, xiv, 99-100, 131-149, 153-182
Sprite display priorities, 144, 161, 179
Sprite positioning, 137-143, 157-161, 177
SQuare Root function, 34, 84, 375
STA, 221, 233, 251, 255
Stack pointer, 214, 222
STATUS function, 34, 84-85, 354, 375
Status register, 214, 354
490 INDEX
~
STEP keyword, (see FOR...TO), 34, 86
STOP, 273, 301-302
STOP command, 34, 41, 86, 375
STOP key, (see RUN/STOP key)
String arrays, constants, variables, 4, 6-9
String expressions, 9, 17
String operators, 9, 16-17
STR$ function, 34, 87, 375
STX, 233, 251, 255
STY, 233, 252, 255
Subroutines, 222, 228-229, 270, 307
Subtraction, 3, 10-11, 16
Sustain, (see A/D/S/R)
SYS statement, 34, 87, 121, 307, 375
TAB function, 27, 34, 45, 88, 336, 375
TANgent function, 34, 88, 375
TALK, 273, 302
TAX, 233, 252, 255
TAY, 233, 252, 255
THEN keyword, (see IF...THEN), 34
TIME function, 34, 89, 375
TIME$ function, 34, 89, 375
TKSA, 273, 302-303
TO keyword, (see FOR...TO), 34
TSX, 233, 253, 255
TXA, 229, 233, 253, 255
TXS, 233, 253, 255
TYA, 229, 233, 253, 255
UDTIM, 273, 303
UNLSN, 273, 304
UNTLK, 273, 304
User port, 355, 359-362
USR function, 34, 90, 307, 375
VALue function, 34, 90, 375
VECTOR, 273, 305-306
VERIFY command, 34, 91, 375
Vibrato, 203
Voices, 187-191
Volume control, SID, 186
INDEX 491
~
WAIT statement, 13-14, 34, 92, 375
XOR, (see WAIT statement), 13-14
X index register, 213, 223-224
Y index register, 214, 223-224
Z-80, (see CP/M)
Zero page, 221-222, 358-359
492 INDEX
~
COMMODORE 64 QUICK REFERENCE CARD
SIMPLE VARIABLES
Type Name Range
Real XY +-1.70141183E+38
+-2.93873588E-39
Integer XY% +-32767
String XY$ 0 to 255 characters
X is a letter (A-Z), Y is a letter or number (0-9). Variable names
can be more than 2 characters, but only the first two are recognized.
ARRAY VARIABLES
Type Name
Single Dimension XY(5)
Two-Dimension XY(5,5)
Three-Dimension XY(5,5,5)
Arrays of up to eleven elements (subscripts 0-10) can be used
where needed. Arrays with more than eleven elements need to be
DIMensioned.
ALGEBRAIC OPERATORS RELATIONAL AND LOGICAL OPERATORS
= Assigns value to variable = Equal
- Negation <> Not Equal To
^ Exponentiation < Less Than
* Multiplication > Greater Than
/ Division <= Less Than or Equal To
+ Addition >= Greater Than or Equal To
- Substraction NOT Logical "Not"
AND Logical "And"
OR Logical "Or"
Expression equals 1 if true, 0 if false
~
SYSTEM COMMANDS
LOAD"NAME" Loads a program from tape
SAVE"NAME" Saves a program on tape
LOAD"NAME",8 Loads a program from disk
SAVE"NAME",8 Saves a program to disk
VERIFY"NAME" Verifies that program was SAVEd without errors
RUN Executes a program
RUN xxx Executes program starting at line xxx
STOP Halts execution
END Ends execution
CONT Continues program execution from line where
program was halted
PEEK(X) Returns contents of memory location X
POKE X,Y Changes contents of location X to value Y
SYS xxxxx Jumps to execute a machine language program,
starting at xxxxx
WAIT X,Y,Z Program waits until contents of location X,
when EORed with Z and ANDed with Y, is nonzero.
USR(X) Passes value of X to a machine language subroutine.
EDITING AND FORMATTING COMMANDS
LIST Lists entire program
LIST A-B Lists from line A to line B
REM Message Comment message can be listed but is ignored during
program execution
TAB(X) Used in PRINT statement. Spaces X positions on screen
SPC(X) PRINTs X blanks on line
POS(X) Returns current cursor position
CLR/HOME Positions cursor to left corner of screen
SHIFT+CLR/HOME Clears screen and places cursor in "Home" position
SHIFT+INST/DEL Inserts space at current cursor position
INST/DEL Deletes character at current cursor position
CTRL When used with numeric color key, selects text color.
May be used in PRINT statement.
CRSR keys Moves cursor up, down, left, right on screen
Commodore Key When used with SHIFT selects between upper/lower case
and graphic display mode.
When used with numeric color key, selects optional
text color
~
ARRAYS AND STRINGS
DIM A(X,Y,Z) Sets maximum subscripts for A; reserves space for
(X+1)*(Y+1)*(Z+1) elements starting at A(0,0,0)
LEN(X$) Returns number of characters in X$
STR$(X) Returns numeric value of X, converted to a string
VAL(X$) Returns numeric value of X$, up to first
non-numeric character
CHR$(X) Returns ASCII character whose code is X
ASC(X$) Returns ASCII code for first character of X$
LEFT$(A$,X) Returns leftmost X characters of A$
RIGHT$(A$,X) Returns rightmost X characters of A$
MID$(A$,X,Y) Returns Y characters of A$ starting at character X
INPUT/OUTPUT COMMANDS
INPUT A$ or A PRINTs "?" on screen and waits for user to enter
a string or value
INPUT "ABC";A PRINTs message and waits for user to enter value.
Can also INPUT A$
GET A$ or A Waits for user to type one-character value; no
RETURN needed
DATA A,"B",C Initializes a set of values that can be used by
READ statement
READ A$ or A Assigns next DATA value to A$ or A
RESTORE Resets data pointer to start READing the DATA list again
PRINT"A= ";A PRINTs string "A=" and value of A
";" suppresses spaces - "," tabs data to next field
PROGRAM FLOW
GOTO X Branches to line X
IF A=1 TO 10 IF assertion is true THEN execute following part of
statement. IF false, execute next line number
FOR A=1 TO 10 STEP 2 Executes all statements between FOR and
corresponding NEXT, with A going from 1 to 10
by 2. Step size is 1 unless specified
NEXT A Defines end of loop. A is optional
GOSUB 2000 Branches to subtoutine starting at line 2000
RETURN Marks end of subroutine. Returns to statement following
most recent GOSUB
ON X GOTO A,B Branches to Xth line number on list. If X=1 branches
to A, etc.
ON X GOSUB A,B Branches to subroutine at Xth line number in list
~
ABOUT THE COMMODORE 64 PROGRAMMER'S REFERENCE GUIDE...
----------------------------------------------------------
Game cartridge compability... spectacular sound... arcade
style graphics... and high caliber computing capabilities
make Commodore 64 the most advanced personal computer in
its class for home, business and educational use.
The COMMODORE 64 PROGRAMMER'S REFERENCE GUIDE tells you
everything you need to know about your Commodore 64. The
perfect companion to your Commodore 64 User's Guide, this
manual presents detailed information on everything from
graphics and sound to advanced machine language techniques.
This book is a must for everyone from the beginner to the
advanced programmer.
For the beginner, the most complicated topics are explained
with many sample programs and an easy-to-read writing style.
For the advanced programmer, this book has been subjected
to heavy pre-testing with your needs in mind. And it's
designed so that you can easily get the most out of your
Commodore 64's extensive capabilities.
C= COMMODORE
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COMMODORE BUSINESS MACHINES (UK) LTD.
675 Ajax Avenue
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Slough, Berkshire SL1 4BG
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9.95 pounds/22056 ISBN 0-672-22056-3
~
*********
The end of the Project 64 etext of the Commodore 64 Programmer's
Reference Guide, first edition.
*********
~
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