Re: Space Duel PCB weirdness

On Mon, 26 Jan 2009 21:19:50 -0600, you wrote:

>Not at all - the processor pins just stop. It really is baffling me - I'm
>looking to get a logic analyzer here sometime this week - I think it's the
>only way to really see what the processor is doing. Unless you have a trick
>up your sleeve? :)

Mmm... personally, I think a logic analyser may be overkill (although if
you happen to have one lying around that you can borrow, more power to ya!
:) ), at least until you've scoped or logic-probed out some of the simpler
possibilities, such as:

        (1) Check pin 6 (NMI*) of the 6502; make it isn't floating or stuck
low. According to the schematic, NMI* should be held permanently high
(along with pin 2 (READY) and pin 38 (SO)) through the 1K resistor at R19.

        (2) Pin 4 (IRQ*) is fed from pin 11 of the 74LS00 @ L3, which also
connects back to pin 10 of the 74LS161 counter @ J4. This counter is
driven by a 3KHz clock at pin 2; make sure this clock is present, and that
the LS161's CLEAR* signal at pin 1 isn't stuck low.

>The watchdog barks, so I disabled it

        (3) *How*, exactly, did you disable it? Make sure pin 40 (RESET*) at
the CPU isn't stuck low or floating...

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"It may be better to live under robber barons than under omnipotent moral
busybodies. The robber baron's cruelty may sometimes sleep, his cupidity may
at some point be satiated; but those who torment us for our own good will
torment us without end, for they do so with the approval of their
conscience." --- (C. S. Lewis)
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solarfox@removethis.triluminary.net (Gary Akins jr.)
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Received on Mon Jan 26 23:56:12 2009