C64 Demo — main.asm

A Commodore 64 intro written in 6502 assembly (compiled with the ACME assembler). The screen shows:

• giant TTG letters in the top half (built from 8×8 bitmaps, drawn with solid block characters),
• TELETYPE GAMES centered below,
• a horizontally scrolling credits line (MR.ZERO - TASNADI ZSOLT / MR.ONE - TARI BALAZS / MR.TWO - TIMAR ZOLTAN / MR.THREE - MEZO BELA),
• WWW.TELETYPEGAMES.ORG,
• SZEGED, 2026.

Build and run

make build       # produce main.prg
make run         # build + launch in VICE (x64sc)
make rebuildrun  # clean rebuild + run
make deps        # on macOS: install acme + vice via Homebrew

Loading the .prg on a real or emulated C64:

LOAD"*",8,1
RUN

Structure of main.asm

1. BASIC stub (from $0801)

A hand-encoded one-line BASIC program (10 SYS 2064) so the user only has to type RUN; it jumps to the machine-code entry point at $0810.

2. Initialization

Border and background are set to black, then screen RAM ($0400) is filled with spaces and color RAM ($D800) with white. Everything is drawn by writing to screen RAM directly — the KERNAL CHROUT routine is not used.

3. Giant letters

Each big letter is an 8×8 bitmap (bigfont, one byte per row, MSB = left pixel). The drawing loop walks the three letters, shifts each bitmap row out bit by bit, and writes an inverse-space block ($A0) plus yellow into color RAM for every set bit. Letters are 8 columns wide with a 2-column gap, so the 28-column logo is centered starting at column 6, row 2.

4. Static texts

Null-loop copies place the screen-code strings (!scr) at fixed, centered screen offsets:

Text	Row	Color
TELETYPE GAMES	12	white
scroller line	14	cyan
WWW.TELETYPEGAMES.ORG	17	light green
SZEGED, 2026	19	light grey

5. Scroller (main loop)

The main loop synchronizes to the display by waiting for raster line $FE ($D012), giving one iteration per frame. Every SCROLL_SPEED (4) frames it shifts row 14 one character to the left and feeds the next character of scrolltext into the rightmost column; the index wraps at the end of the text, so the credits loop forever.

Memory map

$0801 .. $080F   BASIC stub (10 SYS 2064)
$0810 .. ...     machine code + font bitmaps + texts + variables
$0400 .. $07E7   screen RAM (written directly)
$D800 ..         color RAM
$D012            raster line (frame sync)
$D020 / $D021    border / background color