z80_monitor/README.md

Z80 UART monitor

This ROM provides a small interactive monitor on the UART/CTC card at I/O base 20. Connect a terminal at 2400 baud, 8 data bits, no parity, 1 stop bit. Commands are case-insensitive and all numeric arguments are hexadecimal; an optional 0x prefix is accepted.

Command	Action
D 8000	Dump 40 bytes starting at address 8000
D 8000 20	Dump 20 bytes starting at address 8000
W 8000 3E 41 D3 25 C9	Write bytes starting at address 8000
I 20	Read I/O port 20
O 20 57	Write 57 to I/O port 20
G 8000	Execute code at address 8000
HELP	Show the command summary

G transfers control with a return address on the stack, so code ending in RET returns to the monitor. Code that changes the stack pointer, interrupt mode, or UART/CTC setup must restore it before returning.

Build the ROM and programmer-format images with:

make

The outputs are build/metal/monitor.bin (32 KiB ROM image) and build/metal/monitor.prog.bin (compact programmer image).