Undocumented CPU Opcodes
Discussions center on undocumented, illegal, and quirky opcodes in vintage processors like the 6502 and x86/8086, including their encoding, history, microcode, and artifacts from early designs.
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Think more! One would guess that the search for undocumented opcodes yields results...?
Certainly the BCD instructions are not used?
No, but see kiwidrew's comments that discuss undocumented opcodes.
6502 zero page instruction vibes.
Probably an artifact of the Datapoint's instruction decoder unit.
They could have wired those instructions as a NOP, rather than aliasing another opcode...
You mean like the AMX instructions?
Interesting, explaining the encoding of x86 opcodes (opcodes encoded in octal, addressing modes, etc.).
Source on the intel opcode thing?
Do the '040/060 also support this "undocumented instruction"?