The M6800 had a few illegal opcodes, including the (in)famous HCF (Halt and Catch Fire). The following illegal opcodes were revealed in BYTE Magazine, December 1977:
$87: STAA immediate
Does anyone have a quick primer to the way the 6800's compare-and-branch instructions worked internally? I'm referring to the instructions like BLS that compared a value in memory to the accumulator.
I'd like to examine (disassemble and memory dump) and run the SWTBUG
monitor ROM in the SIMH SWTP6800 emulator, but I seem to be
having difficulty getting the devices attached properly, or I'm lost