Re: Sig. analysis on Atari 6502 boards

I found the MAME file tbl6502.c has:

OP(ea) { M6502_ICount -= 2; NOP; } // 2 NOP

so it looks like NOP is 0xEA in 6502 machine language.

Matt Rossiter - Verio Southern California <matt@rossiters.com>
@lists.cc.utexas.edu on 09/20/99 05:46:59 AM

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Subject: Re: Sig. analysis on Atari 6502 boards

I don't know machine language that well, but I thought I remember the
opcode being 0x5f ?? So I guess it would be...

D7 (msb) - GND
D6 - +5v
D5 - GND
D4 - +5v
D3 - +5v
D2 - +5v
D1 - +5v
D0 - +5v

Is that right? I suppose I could try it both ways.

Thanks guys, this'll be fun to try out.....

Matt

_____________________________________________________________________

On Sun, 19 Sep 1999, Jess Askey wrote:

> all you have to do is wire the data lines to the binary equivalent of
NOP... So
> if the NOP is 0x86 (which seems to pop into my head but I can't remember
for
> sure...
>
> D7(msb)- +5V
> D6 - GND
> D5 - GND
> D4 - GND
> D3 - GND
> D2 - +5V
> D1 - +5V
> D0 - GND
>
> If 0x86 isn't the opcode for NOP then this is wrong of course. But you
get the
> idea.
>
>
>
> Matt Rossiter - Verio Southern California wrote:
> >
> > I have some Kurz Kasch instructions for doing signature analysis on
Atari
> > 6502 boards.
> >
> > Step #2 says "Plug in 6502-A (Atari) NOP into socket with the textool
> > locking handle at the pin 1 location".
> >
> > - you then put the cpu into the socket and close the locking handle.
> >
> > - the signature analyser is connected by hooking clock to pin 37, start
> > and stop to pin 25 and ground to pin 21.
> >
> > My question is - how would you go about making a 6502-A NOP? Can you
do
> > this by just grounding certain pins on the cpu socket or is it more
> > involved? Would this set up work for comparing signatures in most of
the
> > Atari manuals or do you actually need to use the CAT box?
> >
> > Just wondering...
> >
> > Matt
>
>
Received on Mon Sep 20 06:50:54 1999