Gregory's Serveryou know how the rev A 6502 from 1975 had a bug in ROR? turns out not to be true. https://youtu.be/Uk_QC1eU0Fg
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 @tubetime Very interesting, didn't know. (BTW those 1975 pearly white ceramic packages look very cool.) @tubetime thanks for posting this. The "conventional" explanation of this issue never sat well with me. I've seen some interesting silicon bugs in my time, but the outcome of running ROR on a rev A 6502 sounded a lot more like an undecoded instruction rather than a logic error in an intentional instruction. @tubetime this was an exceptionally good video. Thanks for the great explanation!   @rhialto i forgot to mention it in the video, but rotate left is kinda incredible. it just uses the ALU to add the number to itself. carry in, carry out just like a regular add! |
@tubetime Your comment regarding the 6502's use in the 2600 could have come with a small asterisk . The 2600 used a 6507, though of course the internal silicon was the same so it would have been hit by the same "missing feature" 🙂 BTW, also wanted to say that you do amazingly amazing work!