RE: Testing Cinematronics CPU's

At 11:57 AM 12/31/98 -0600, you wrote:
>On Thu, 31 Dec 1998, Keith, Brendan wrote:
>
>> It's not just for diagnostics. If you power up a previously working game
>> but the board has died, the monitor won't have to go to the corner and
>> blow out. My AA just did that last week.
>>
>
> When the board dies, the board will conceivably pull the inputs to
>the monitor in some "random" way, since I don't think they get tri-stated.
>
> Since your pull-up/pull-down would have to be weak enough to not
>affect the normal operation of the monitor, it wouldn't affect the
>"failure-mode" operation, either, where the game board is pulling the,
>inputs, just not in the way you'd like it to....(i.e. all high or all
>low might be common cases...)
>
>Joe
>

What about a little add on board to do the following: Add a tri-state
buffer and after that add Brendan's pullup and pulldown scheme. Have the
buffer control look at the CPU's reset circuitry and if the reset is on or
oscillating keep the buffer tri-stated. A one shot 555 setup could be used
for that.

-Chris

--
Christopher V. Moore -- Principal Engineeer
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