# 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:

```sh
make
```

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