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I may have found another error in MAME's disassembler. 0f5b: 10 4a DECA 0x4A is DECA, but 0x104A is DECD instead. On a 6809 $104a is a nonstandard version of DECA. $4a is officially undefined on opcode page 2. On a 6309 $104a is DECD Mame's debugger will show the correct disassembly depending on wh...

I've also noticed (by comparing my disassembly with MAME's) that I'm showing opcode 0xCD as LDQ Immediate (according to the instruction set) while MAME shows: 31f0: cd XHCF Could it be that XHCF is used if its prefixed by $10 or $11? $CD on a 6809 is XHCF. $CD on a 6309 is a LDQ Immediate. Mame has...

robcfg wrote: ↑Thu May 01, 2025 10:26 am I'm going through your table and noticed that postbyte $8A (F,X) is marked as having another byte following it, while $AA (F,Y) does not.
Is that an actual useless byte that only affects the ,X form or is it a typo in the table?

Yes. A typo.

The 6309 indexed addressing mode opcodes added to the existing 6809 indexed addressing modes without changing how the 6809 codes worked.

I originally wanted to disassemble the mnemonics a little differently, but I couldn't get buy in from the other MAMEDevs.

That's my doing. I took the behavior described here: https://github.com/hoglet67/6809Decoder/wiki/Undocumented-6809-Behaviours#undocumented-page-2-opcodes https://github.com/hoglet67/6809Decoder/wiki/Undocumented-6809-Behaviours#undocumented-page-3-opcodes https://github.com/hoglet67/6809Decoder/wik...

I'm a little confused with the terms soft and hard reset. I just did some testing on my CoCo 3 with a Multi-pak. I had a SDC in slot 4, Clowns & Balloons in slot 1, and the switch to slot 4. I powered on the machine and I got the SDC-DOS BASIC prompt. I typed in POKE &HFF7F,0 and it immediately boot...