6502 illegal opcodes testing

Discuss technical or other issues relating to programming the Nintendo Entertainment System, Famicom, or compatible systems.

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Oziphantom
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Joined: Tue Feb 07, 2017 2:03 am

6502 illegal opcodes testing

Post by Oziphantom » Wed Feb 13, 2019 12:36 am

On the Commodore side we speculate that different versions of the CPU might not have the same illegal opcodes. This is because they are dependent upon the exact layout of the ROM, traces and in some cases length of the traces and process used.

Has anybody seen or done testing of the full set against the NES CPU, R6502, GTE6502, 6507 etc

lidnariq
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Joined: Sun Apr 13, 2008 11:12 am
Location: Seattle

Re: 6502 illegal opcodes testing

Post by lidnariq » Wed Feb 13, 2019 12:56 am

I recall some random source stating that a very wide breadth of NMOS 6502 variants have been tested, and for every instruction that is not $8B ("sax #immed"), $AB ("lax #immed"), nor some of the KIL instructions, everything else works identically ... although sometimes inscrutably.

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