WDC 65C02 SXB Monitor

A machine-language monitor for the WDC W65C02SXB single-board computer. The stock ROM that ships with these boards comes with a software that will only work with WDC's TIDE, which I was not able to get to work on Windows 11. So instead this replaces the stock ROM with a proper ROM monitor. The board's USB port is connected to an FT245RL USB-parallel FIFO which the monitor uses for as the debug port.

As a reminder, this machine uses a straightfoward ~32 K RAM + I/O space + 32 K ROM memory map:

$0000-$7EFF: RAM
$7F00-$7FFF: I/O space (USB port on VIA2 at $7FE0-$7FFF)
$8000-$FFFF: ROM

This was adapted from smon6502, itself an adaptation of the SMON monitor originally published in the German magazine 64'er in 1984. I say adapted because this is not a straight port: differences in interrupt handling between the original 6502 and the 65C02 required rewriting the trace and breakpoint code. The orignal source was written in VASM and used fixed addressing and required the C64's KERNAL ROM.

This is a rewrite specifically for the W65C02SXB, but using the cc65 toolchain and relocatable asm so it's likely portable to other computers.

• Memory fill, copy, compare, and dump in hex and ASCII
• Integrated disassembler with 65C02 extended instruction set support
• Search memory by byte sequence, opcode arguments, and addresses references
• Load Intel HEX files from the terminal into memory
• Trace / single-step / breakpoint execution
• Address relocation (convert + copy)
• Immediate evaluation (hex to decimal, binary to hex, etc., integer arithmetic)
• Indirect jump through vectors (G (addr))
• A W65C02SXB simulator implemented with py65

• cc65 toolchain (ca65, ld65, cl65, ar65)
• minipro (for flashing the ROM chip)
• GNU Make

Note: the source uses the c_sp zero-page name, which requires a cc65 built from git master (the 2.19 release still calls it sp). The Makefile auto-detects the cc65 data directory in /usr/local/share/cc65 and /usr/share/cc65; override with make CC65_DATA_DIR=... if yours lives elsewhere.

The SBC uses a 128 KB ROM chip, but only the top 32 KB is visible to the CPU. The ROM image is padded with $FF to 128 KB for flashing.

You'll probably need a PLCC-32 to DIP-32 and a PLCC puller to flash the ROM chip, as well as a programmer. I was never able to get the board's built-in USB to work, which is why I'm using this in the first place.

make test runs the ROM image under a simulated W65C02SXB and drives the monitor through an emulated terminal, checking the responses. The simulation uses py65's 65C02 core with the board's memory map, and emulates the FT245 USB FIFO.

Requirements: python3 and py65 (pip install -r test/requirements.txt).

The monitor will start on NMI or BRK.

Type H at the monitor prompt to display the built-in help.