This ROM provides a small interactive monitor on the UART/CTC card at I/O base 20. At reset, a small ROM bootstrap copies the monitor into the top 16 KiB of RAM at C000-FFFF and starts it there. Only the occupied vector/code bytes are stored and copied; uninitialized data is cleared directly in high RAM. The low ROM can subsequently be disabled without taking the monitor, its data, or its interrupt table away. Runtime code and vectors occupy the lower part of this window, globals begin at F000, and the stack grows downward from FFFF; no RAM below C000 is used.

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). The ROM layout is:

0000-007F: reset/copy bootstrap
0080...: compact vector/code image copied to RAM starting at C000
Remaining bytes: unused and available for additional ROM content

The monitor executable starts at C080; its IM 2 vector table is at C040. monitor.prog.bin ends immediately after the occupied payload, while monitor.bin remains a complete 32 KiB chip image.