https://github.com/codesleuth7/northstar_horizon_z80_rom
The NorthStar Horizon is a S-100 bus Z80 computer from 1977. This ROM monitor
was created as part of a restoration project. The initial need was a diagnostic
to isolate and troubleshoot basic hardware problems. The minimum hardware
required for this ROM was only the Z80 CPU and console serial port. Basic
function without memory was a design goal to assist with memory troubleshooting.
Memory from this era was a common source of failure for many retro computers.
Design requirements:
- No RAM, which includes no stack.
- Relative code, no fixed addressing.
- Modified Z80 CPU card uses ROM 2716, 2048 bytes max size
Features:
- Map Memory
- Test Memory
- Display Memory
- Edit Memory
- Go to address
- Boot - E800
- Fill Memory
- Loop address - for testing
- Intel-HEX load
Assembler:
Develment environment was Ubuntu using z80asm. No preprocesser in this version which
should make it easier to port to other z80 assemblers.
For example:
$ z80asm -onsz80rom.bin -lnsz80rom.lst nsz80rom.mac
This ROM requires 2K and works with a 2716 using this on the CPU card:
https://deramp.com/downloads/north_star/horizon/roms/ZPB-A%20PROM%20Mod.pdf