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A comment on 6502 “Illegal” Opcodes Demystified. Parent comment

Re:6502 “Illegal” Opcodes Demystified by nicetryguy on Sunday June 06, 2021 @01:28PM (#27414671)
There is a story about how BIT sets bit 6 into the overflow flag, and this was documented on a piece of parchment paper in pencil!

http://www.6502.org/tutorials/vflag.html

Either way, every transistor in the processor has been broken down completely, and even recreated in a visual simulation:

http://visual6502.org/

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Re:6502 “Illegal” Opcodes Demystified by masswerk on Sunday June 06, 2021 @01:42PM (#27414779)
The overflow flag and its intrinsics was quite a mystery for a while.

(Related fun fact: There is no such thing as a break flag, it just gets inserted, whenever the the status register is pushed to the stack by an instruction, i.e. by software, as opposed to a hardware interrupt. This is also, why it is commonly shown as 1, because this is the value it would show up with, if there was a PHP or BRK instruction at the given time, which is also: always. But this is really just a virtual state and there is no such flag in the CPU.)

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