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:
In addition, this article reveals these additional illegal opcodes:
HCFwith slightly different behavior
Okay, that's all well and good. I only listed them all because the first article I linked to, from BYTE Magazine in December 1977, says the following:
Some of those codes seem to be just NOPS: they do nothing. Others change the flags in the condition code register according to some pattern that is, as yet, undeciphered.
What are these additional illegal opcodes on the M6800, which are not listed above? And has someone deciphered their flag changing patterns in the intervening 42.5 years?