• Jesus@lemmy.world
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    22 hours ago

    Found an article in the same time it took to write a comment.

    https://www.pagetable.com/?p=406#%3A~%3Atext=The+MOS+6502+CPU+was%2Cgoing+on+in+these+chips.

    The MOS 6502 CPU was introduced in September of 1975, and while the documentation described the three shift/rotate instructions ASL, LSR and ROL, the ROR instruction was missing – the documentation said that ROR would be available in chips starting in June 1976. In fact, the reason for this omission was that the instruction, while being present, didn’t behave correctly. Only few 6502s with the defect are in existence, and nobody seemed to have checked what was actually going on in these chips.