Undocumented 'NOP's are not handled properly

X16Community / x16-emulator

Emulator for the Commander X16 8-bit computer

BSD 2-Clause "Simplified" License

183 stars 39 forks source link

Open Yazwh0 opened 1 week ago

Yazwh0 commented 1 week ago

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 commented 1 week ago

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

Yazwh0 commented 1 week ago

On hardware: