Re: Signature Analysing Question

Mark Shostak wrote:
>
> In message "Signature Analysing Question", pinball@istar.ca writes:
>
> > Hi, Mark!
> >
> > You can also wire up a special CPU that is locked into "NOP" function,
> > this will generate a nice pattern for SI.
> >
> > John :-#)#
>
> Hi John,
>
> I've done that, but for some reason on Atari boards, the NOP configuration
> does not yield stable signatures. So far I've been too busy to figure out
> why, so I just use the CAT box. However, it does work well on Space Inva-
> ders.
>
> Cheers,
> Mark
>
> P.S. Come to think of it, it may just be the phase difference between ph.1
> and ph.2 of the clock. With the CAT, they're in phase, but with the
> NOP they're not. Note to self: check the clocks.

Hi!
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...
John :-#)#

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