Wozmon (written by Steve Wozniak in 1976) created for the MC6809/HD6309 and the 6800-family of peripherals.

The 6809Mon hex monitor runs in EEPROM (32k) space from address 0x8000. The input buffer is placed in RAM (16k) at 0x0100 to 0x017F, as well as eight page zero variables. The stack is initialised to the top of RAM at 0x03FF.

The monitor uses UART over the 6850 ACIA; 8 bits, 1 stop bit, no parity. Baudrate is generated by dedicated hardware (counters and some gates) and the ACIA uses 16x division. The ACIA is mapped to addresses 0x5000/0x5001.

I use Vasm oldstyle to assemble this project.

Currently, 6809Mon is 265 bytes in size. I'm willing to accept any kind of space optimisations to fit this into a 256 byte limit like the original Wozmon, but not with much inter-dependent magic. I'm also not that familiar with the 6809. Features such as the direct page, and probably some other things, are left out which adds room for improvement in the future.