Re: Off definition request for design help

On Wed, 7 Jan 1998 21:57:39 -0800, "David Shoemaker" <davids@wolfenet.com>
wrote:

>>You just asked the question wrong, try...
>Very good point Zonn :)
>
><Ahem>
>
>>I am working on a [Cinematronics] multigame rig and in the process of doing
>the
>>control panel re-routing per game I just don't like my design. As there
>are
>>many of you here who have very much more EE design knowledge than I, I have
>>been wanting to ask forever.
>>
>>My question is:
>
>I am attempting to route say 8 TTL control lines from point a to point b
>with them being re-arraigned as needed for each game. I want to be able to
>tie this into a dip switch which picks the "Mode" of the routing.
>
>I can do this with a large amount of digital switches but as I can only do
>one mode in no less than 3 of these parts it is a very cumbersome process as
>I have say 8 modes to perform.
>
>Graphically I am doing something like this (on 4 modes with 4 lines to save
>space)
>
>Mode 1 2 3 4
> a a d d
> b b b c
> c d c b
> d c a a
>
>Where a-d is the source pin designator and its vertical position in the
>chart is its destination pin.
>
>I know there must be some way to load the "mode" map into some sort of
>controller which would then route signals to the appropriate place.
>
>Ultimate goal would be 16 i/o's with routing. And 8 modes. I am willing to
>break this up into as many as 4 parts handling 1/4th the load but I am
>really trying to reduce part count. Cost is not nearly as much an issue but
>my minimal knowledge of microcontrolers / PLD / GAL / (and the rest of the
>alphabet soup that goes around here sometimes :) and there capabilities is.
>
>One idea I had was using 2 large 8bit EPROM's with the inputs from the
>control panel being the address select (8 bit + 3 mode select bits) and data
>outs being the data out to the game. But this really seems like a large
>waste and I am not sure I can reasonably get EPROM's to perform fast enough
>for my purpose.

The cleanest would be a self contain microprocessor (like the PIC). You could
get by with just the PIC, a couple of resistors and a cap or two, the dipswitch,
and possibly a voltage regulator. Then whatever connectors you would use to
wire everything up to the control panel.

This would of course require software and the ability to burn PICs. PIC burners
can be had fairly cheap. (<$100 I've seen as low as $40 on the net)

Large EPROMs would work great and are a magnitude (at the very least) faster
than what you need, don't worry about speed. They only problem you might have
with EPROMs is glitches as they change states. It is possible for data lines to
glitch as the address decoder of the EPROM ripples through it's logic looking
for the right data. I doubt it will be a problem (the glitches, if present, are
*very* fast). Any glitch that might show up will most likely be ignored by the
debounce logic of the game. You could synchronously clock the data through the
EPROMs but this would take a bit of external logic.

All in all the EPROMs would be your simplest solution if you have an EPROM
programmer.

-Zonn

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Received on Thu Jan 8 10:47:04 1998