# KERNAL (C64 ROM Operating System)

Source: https://www.c64-wiki.com/wiki/Kernal

The KERNAL is Commodore's low-level Operating System. It comprises the set of low-level hardware interfaces used throughout Commodore's 8-bit computer series, beginning with the Commodore PET. (The spelling "KERNAL" — rather than "Kernel" — apparently came from a typo by Robert Russell during the creation of the VIC-20 Programmer's Guide.)

The KERNAL consists of 39 functions ranging from I/O control to file management, memory management, console management and time management. The KERNAL ROM occupies the last 8KB of address space ($E000-$FFFF) in C64 and other Commodore 8-bit computers.

KERNAL functions are accessible via a jump table at the end of addressable memory ($FF81-$FFF3).

## KERNAL Jump Table

| Name | Address Hex | Address Dec | Function |
|------|-------------|-------------|----------|
| ACPTR | $FFA5 | 65445 | Input byte from serial port |
| CHKIN | $FFC6 | 65478 | Open channel for input |
| CHKOUT | $FFC9 | 65481 | Open a channel for output |
| CHRIN | $FFCF | 65487 | Get a character from the input channel |
| CHROUT | $FFD2 | 65490 | Output a character |
| CIOUT | $FFA8 | 65448 | Transmit a byte over the serial bus |
| CINT | $FF81 | 65409 | Initialize the screen editor and VIC-II |
| CLALL | $FFE7 | 65511 | Close all open files |
| CLOSE | $FFC3 | 65475 | Close a logical file |
| CLRCHN | $FFCC | 65484 | Clear all I/O channels |
| GETIN | $FFE4 | 65508 | Get a character |
| IOBASE | $FFF3 | 65523 | Define I/O memory page |
| IOINIT | $FF84 | 65412 | Initialize I/O devices |
| LISTEN | $FFB1 | 65457 | Command a device on the serial bus to listen |
| LOAD | $FFD5 | 65493 | Load RAM from device |
| MEMBOT | $FF9C | 65436 | Set bottom of memory |
| MEMTOP | $FF99 | 65433 | Set the top of RAM |
| OPEN | $FFC0 | 65472 | Open a logical file |
| PLOT | $FFF0 | 65520 | Set or retrieve cursor location |
| RAMTAS | $FF87 | 65415 | Perform RAM test |
| RDTIM | $FFDE | 65502 | Read system clock |
| READST | $FFB7 | 65463 | Read status word |
| RESTOR | $FF8A | 65418 | Set the top of RAM |
| SAVE | $FFD8 | 65496 | Save memory to a device |
| SCNKEY | $FF9F | 65439 | Scan the keyboard |
| SCREEN | $FFED | 65517 | Return screen format |
| SECOND | $FF93 | 65427 | Send secondary address for LISTEN |
| SETLFS | $FFBA | 65466 | Set up a logical file |
| SETMSG | $FF90 | 65424 | Set system message output |
| SETNAM | $FFBD | 65469 | Set up file name |
| SETTIM | $FFDB | 65499 | Set the system clock |
| SETTMO | $FFA2 | 65442 | Set IEEE bus card timeout flag |
| STOP | $FFE1 | 65505 | Check if STOP key is pressed |
| TALK | $FFB4 | 65460 | Command a device on the serial bus to talk |
| TKSA | $FF96 | 65430 | Send a secondary address to a device commanded to talk |
| UDTIM | $FFEA | 65514 | Update the system clock |
| UNLSN | $FFAE | 65454 | Send an UNLISTEN command |
| UNTLK | $FFAB | 65451 | Send an UNTALK command |
| VECTOR | $FF8D | 65421 | Manage RAM vectors |

## C64 U4 Kernal ROM Failure Symptoms

- Blank screen, no border
- Most cartridges don't work, but a few (e.g. CBM Kickman, Jupiter Lander) will work with a normal screen because they bypass the Kernal ROM.

## See also

- Full KERNAL listing: http://unusedino.de/ec64/technical/aay/c64/krnromma.htm
- Commodore 64 Programmer's Reference Guide (free): http://www.zimmers.net/cbmpics/cbm/c64/c64prg.txt