The following addresses (except for C2F2, C8E6, FFFA, FFFC and FFFE) are the entry points for some useful routines in BASIC and COS. Note that most are not documented by Acorn, and so may change in future ROMs.
| Address | |
| C2F2 | Entry point for BASIC
interpreter; locations 5 and 6 should point to the start of the BASIC program |
| C278 | File Shut - just RTS |
| C589 | Print4-byte binary integer from #16,#25,#34, #43 (MSB) |
| C8E6 | Auto start address for routine loaded from tape. |
| C9D8 | BRK service routine;
retrieves PC from stack, stores it in 0, then goes to BASIC routine pointed to by 10,11 (normally C9E7) |
| F6E2 | Plot mode 0 |
| F73B | Plot mode 1 |
| F754 | Plot mode 2 |
| F76D | Plot mode 3 |
| F7AA | Plot mode 4. See block zero RAM |
| F7D1 | Output ASCII string
from the calling routine following 'JSR F7D1'. Returns calling routine at first byte with bit 7 = 1. Uses A,X,Y. |
| F802 | Print A as two hex digits. A destroyed. |
| F87E | Convert ASCII hex
char in A to binary. A destroyed. Returns C=1 if char was not ASCII '0' to '9' |
| F89E | Converts ASCII hex
string at 0100,Y to 16 bit binary in 0,X and 1,X. Uses
2,X. Destroys A. Returns with Y pointing to first non-hex character, Z=1 if first character is not ASCII '0' to '9' |
| F8EF | Interpret string
starting at 0100 as an Operating System command. Uses all registers. Legal commands are: 'CAT', 'LOAD', 'SAVE', 'RUN', 'MON', 'NOMON', 'FLOAD' and 'DOS'. The latter causes a jump to E000 |
| F96E | Load cassette file. Enter with X pointing to the first of five data bytes in zero page RAM; 0,X and 1,X pointing to the file name string, 2,X and 3,X pointing to the first byte to be loaded. 4,X bit 7 should be 0 to use the file's start address |
| FAE5 | Save cassette file. Enter with X pointing to the first of 10 data bytes in zero page RAM; 0,X and 1,X pointing to the file name string, 2,X and 3,X pointing to the reload address 4,X and 5,X pointing to the execution address 6,X and 7,X pointing to the first byte to be saved 8,X and 9,X pointing to the last byte to be saved plus one |
| FB83 | Wait X/60 seconds. Returns with X=0. Other registers preserved |
| FBEE | Get byte from tape,
return with it in A. X and Y preserved Byte added to checksum at 00DC |
| FC38 | Prints 'PLAY TAPE' if
flag C=1, or 'RECORD TAPE' if C=0. Then waits for a key press before returning. Returns with A=13, X and Y destroyed. |
| FC40 | Prints 'REWIND TAPE',
then waits for a key press before returning with A=13. X and Y destroyed. |
| FC7C | Put byte to tape. All registers preserved. Byte added to checksum at 00DC. |
| FD1A | Bleep. All registers destroyed. |
| FD44 | Invert character at
current cursor position. See page zero RAM locations DE to E0. A and Y destroyed. |
| FE52 | Write ASCII character
in A to printer and VDU (if enabled). Control characters recognised and acted upon. All registers preserved. |
| FE55 | As FE52 but does not write to printer. |
| FE66 | Wait for start of VDU fly-back (blanking) period. All registers preserved. |
| FE71 | Scan key (except for
CTRL, SHIFT, RPT and BRK). Returns with flag C-1 if no key pressed, else C=0 and Y = key number. All registers destroyed. |
| FE94 | Wait for key press then return with its ASCII code in A. X and Y preserved. |
| FEFB | Write ASCII character
in A to printer (if enabled). If A=02 (STX), enable printer. If A=03 (ETX), disable printer. All registers preserved. |
| FFCB | OSSHUT; normally calls C278 (RTS) |
| FFCE | OSFIND; normally calls FC38 |
| FFD1 | OSBPUT; normally calls FC7C |
| FFD4 | OSBGET; normally calls FBEE |
| FFDD | OSSAVE; normally calls FAE5 |
| FFE0 | OSLOAD; normally calls F96E |
| FFE3 | OSRDCH; normally calls FE94 |
| FFE6 | OSECHO; normally calls FE94 then FE52 |
| FFE9 | OSASCI; normally calls FE52 |
| FFED | OSCRLF; normally calls FE52 to print CR/LF |
| FFF7 | OSCLI; normally calls F8EF |
| FFFA | NMI vector; normally contains FFC7 |
| FFFC | Reset vector; normally contains FF3F |
| FFFE | IRQ/BRK vector; normally contains FFB2 |
Note: #C014 input routine in #100. Y register must be zero.