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Undocumented 'NOP's are not handled properly #299

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Yazwh0 opened this issue Sep 9, 2024 · 2 comments
Open

Undocumented 'NOP's are not handled properly #299

Yazwh0 opened this issue Sep 9, 2024 · 2 comments
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@Yazwh0
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Yazwh0 commented Sep 9, 2024 •
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There are two nops that act like a LDA $abcd but does not store the value in a register. The opcodes are $dc, $fc.

This 'dummy' read doesn't happen. Also the PC is not incremented by 3, but only 1. Possibly because pagetable.com table have these incorrectly listed? https://www.pagetable.com/c64ref/6502/?cpu=65c02&tab=2#NOP

I suspect $5C also is wrong (as its also wrong on pagetable), but I've not yet been able to check this vs hardware.

Edit: $5c is apparently three bytes as well.
@Yazwh0
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Yazwh0 commented Sep 9, 2024

Updated the port tester for these two opcodes. If F6 doesn't display 2 lines then the opcode isn't supported.

dataport.zip

@Yazwh0
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Yazwh0 commented Sep 9, 2024 •
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On hardware:

image

@mooinglemur mooinglemur added the bug Something isn't working label Sep 11, 2024
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@mooinglemur @Yazwh0