This is Eric Smith's faithful translation of the Apple-1 ROM monitor (wozmon) to the Motorola 6800 (M6800) microprocessor.
See YouTube demo and blog posts (#1, #2).
- Build and install the AS Macro Assembler http://john.ccac.rwth-aachen.de:8000/as/
- Run
make
When making modifications, symbol addresses should generally be preserved in order to maintain compatibility with any client software that makes use of the monitor.
In particular, the following entry points are documented in the original Apple-1 manual (addresses shown here are for this 6800 version):
| Symbol | Address | Description |
|---|---|---|
| GETLINE | $FF21 | monitor entry point (jumping to $FF21 will enter monitor and echo carriage return. You can then examine memory locations with the monitor.) |
| ECHO | $FFB4 | prints one byte (ASCII) (data from ACC A, contents of ACC A not disturbed. Example: BD FF B4 (JSR ECHO)) |
| PRBYTE | $FFA2 | prints one byte (HEX) (data from ACC A, contents of ACC A disturbed.) |
| PRHEX | $FFAA | prints one hex digit (data from four least significant bits of ACC A, contents of ACC A disturbed.) |
RAM locations $24 to $2F are used by the monitor and should be avoided by client software that makes use of the monitor.
NOTE: This version of the monitor uses RAM locations $30 to $38 as vectors for IRQ, SWI, and NMI interrupts, so use of these locations for other purposes in user software must also be avoided if those interrupts may occur in the system.
Refer to the assembly listing (a1mon68.lst) for additional symbol addresses.