Arlet (and others),

I got confused by following the state machine decoder for undocumented opcodes. Could you please clarify what the core does? Undefined? Random stuff? Matching 6502 for all or some instructions (which ones)? Any 65C02 or Rockwell or WDC instructions?

Thanks, and sorry if it's been covered elsewhere (couldn't find a clear answer).

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In theory, there is no difference between theory and practice. In practice, there is. ...Jan van de Snepscheut

The behavior for undocumented opcodes is undefined. This was done on purpose, to allow the synthesis tools to pick the smallest implementation for the documented opcodes. The designers of the NMOS 6502 took a similar approach, but because their implementation was completely different, the behavior of the undocumented opcodes will be different too. In any case, you should not use any of the undocumented opcodes, unless you modify the code to provide support for them.

Just to be clear, are the following instruction considered undefined?

80 BRA rel
12 ORA indirect
32 AND indirect
52 EOR indirect
72 ADC indirect
92 STA indirect
B2 LDA indirect
D2 CMP indirect
F2 SBC indirect
04 TSB zeropage
14 TRB zeropage
34 BIT zpg,X
64 STZ zpg
74 STZ zpg,X
89 BIT imm
1A INC A
3A DEC A
5A PHY
7A PLY
DA PHX
FA PLX
0C TSB absolute
1C TRB absolute
3C BIT abs,X
7C JMP ind,x
9C STZ absolute
9E STZ abs,x

Thank you

_________________
In theory, there is no difference between theory and practice. In practice, there is. ...Jan van de Snepscheut

Correct. Only NMOS instructions are supported, the green ones from this table