Questions tagged [undocumented-opcodes]

Opcodes available in a processor that are not part of its documented instruction set.

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Undocumented ModR/M byte combinations

The reason I am asking this question is because I was trying to compile a list of all 8086 opcodes, regardless of whether or not they are documented. The list is just for fun, the documented opcodes + ...
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Behavior of lesser known illegal M6800 opcodes

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: $14: NBA $87: STAA immediate $C7: ...