Re: Signature Analyzing Question

David Shoemaker (RhoTech) wrote:
> >
> > > You also need to disable the watchdog reset. I lift the reset pin on my
> > > nop test cpu's and make a simple reset with a capacitor and pullup
> > > resistor. The nops that I make are just the cpu with the legs bent back
> > > over the body of the chip, wire the data pins (bent back) to the NOP
> > > instruction, lift the reset pin, and bend it over, then conect the mess
> > > to the +5 and Gnd legs (carefully). Works well...
> > >
> > What exactly are the data pins for the NOP instruction?
> >
> > David
 
 Hi, David (and others)!
 That depends on the processor. EAch type (Z80, 6502, etc) has it's own
 code for a NOP instruction. You need to look it up in the assembly code
 set for the cpu. For instance for the 6502 you dig out a Rockwell data
 book, and looking on the Instruction Code Summary page you find that
the
 NOP instruction is "EA" in hex. So you bend up the legs as follows:
 D7 D6 D5 D4 D3 D2 D1 D0
 H H H L H L H L
     "E" "A"
 Tie the "H"s to the +5Vdc leg (pin 8)(fussy folks use a 330Ohm resitor
 on each D, but it works if tied), and tie the "L"s to ground (pin 1 or
 21).
 Then bend up the Reset leg (pin 40) and connect it to the + lead of a
 10/16Vdc cap, the ground of hte cap to a ground leg (1 or 22), and a
10K
 pull up resistor on pin 40 (and 10ufd cap) to +5 (pin 8). You now have
a
 6502 NOP. Kinda ruins the 6502 fr any other job, but we all must make
 sacrifices in the cause, eh?
 John :-#)#

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