45 lines
1.9 KiB
Markdown
45 lines
1.9 KiB
Markdown
# Z80 UART monitor
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This ROM provides a small interactive monitor on the UART/CTC card at I/O base
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`20`. At reset, a small ROM bootstrap copies the monitor into the top 16 KiB of
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RAM at `C000-FFFF` and starts it there. Only the occupied vector/code bytes are
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stored and copied; uninitialized data is cleared directly in high RAM. The low ROM can subsequently be disabled
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without taking the monitor, its data, or its interrupt table away. Runtime code
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and vectors occupy the lower part of this window, globals begin at `F000`, and
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the stack grows downward from `FFFF`; no RAM below `C000` is used.
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Connect a terminal at **2400 baud, 8 data bits, no parity, 1 stop bit**.
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Commands are case-insensitive and all numeric arguments are hexadecimal; an
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optional `0x` prefix is accepted.
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| Command | Action |
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| --- | --- |
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| `D 8000` | Dump 40 bytes starting at address 8000 |
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| `D 8000 20` | Dump 20 bytes starting at address 8000 |
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| `W 8000 3E 41 D3 25 C9` | Write bytes starting at address 8000 |
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| `I 20` | Read I/O port 20 |
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| `O 20 57` | Write 57 to I/O port 20 |
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| `G 8000` | Execute code at address 8000 |
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| `HELP` | Show the command summary |
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`G` transfers control with a return address on the stack, so code ending in
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`RET` returns to the monitor. Code that changes the stack pointer, interrupt
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mode, or UART/CTC setup must restore it before returning.
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Build the ROM and programmer-format images with:
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```sh
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make
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```
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The outputs are `build/metal/monitor.bin` (32 KiB ROM image) and
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`build/metal/monitor.prog.bin` (compact programmer image). The ROM layout is:
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- `0000-007F`: reset/copy bootstrap
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- `0080...`: compact vector/code image copied to RAM starting at `C000`
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- Remaining bytes: unused and available for additional ROM content
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The monitor executable starts at `C080`; its IM 2 vector table is at `C040`.
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`monitor.prog.bin` ends immediately after the occupied payload, while
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`monitor.bin` remains a complete 32 KiB chip image.
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