I'm working on some Ghidra loader and filesystem modules for 80s microcomputers.
I started work on a Loader for .cas tape image files for the TRS-80 CoCo because Ghidra suports the 6805 CPU. (It also supports the M68HC05TB and MC68HC908QY4)
I never used the CoCo or anything with a 6809 back in the day so wasn't accustomed to its instructions. I am used to a few other instruction sets though. Anyway I assumed 6805 and 6809 would be quite that using Ghidra for CoCo and Dragon 32 binaries would be useful.
But when I got my loader module to the point it was ready to test I found it did not produce code for the CoCo's ROM that matched disassemblies on the Internet. Many bytes could not be decoded into instructions at all.
But when I search for the 6805 I can't find information saying the instruction sets are substantially different, though they only give the impression it should be quite close to the 6809 rather than outright saying it.
So have I made a wrong assumption, have I mixed something up on Ghidra, or do the two similarly named chips have totally different instruction sets? Should I be able to disassemble code for these '80s machines using Ghidra if I set it properly?
(I'm sure there are other disassemblers but I'm only working with Ghidra for this project.)