Posted By
MIRKOSOFT
on 2015-03-02
09:13:30
|  What does 7501/8501 opcode $FB? 6502 it has as illegal ISC/ISB
Hi!
I'm learning more about TED Series computers.
I need to say that I don't know if is instruction set identical with 6502 also in illegal/undocummented opcodes...
So, Q is simple: What does opcode with hex. value $FB ? 6502 it has as illegal ISC/ISB opcode...
And if are instruction sets in case of illegal/undocummented opcodes different where to find any description of undocummented (illegal) opcodes?
Thank you for every reply.
Miro
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Posted By
gerliczer
on 2015-03-02
10:31:53
| Re: What does 7501/8501 opcode $FB? 6502 it has as illegal ISC/ISB
The Commodore 6502 derived CPUs work exactly the same except different number of embedded port bits are connected to pins and different clock and interrupt inputs are available. All documented and undocumented instructions work the same. The instabilities in undocumented instructions are also the same.
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Posted By
Luca
on 2015-03-02
11:13:50
 | Re: What does 7501/8501 opcode $FB? 6502 it has as illegal ISC/ISB
ISC {adr,Y} = INC {adr,Y} + SBC {adr,Y}
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Posted By
MIRKOSOFT
on 2015-03-02
13:25:45
| Re: What does 7501/8501 opcode $FB? 6502 it has as illegal ISC/ISB
Thank you boys!
This I need to know. I know differences between 6502 and 8502 and 7501/8501, now I know that also illegal opcodes are the same like 6502, 8502 and x501 too...
Miro
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