GAL16V8 as a modern substitute for a 7447?

[Ethan Dicks]

On Sat, Dec 08, 2007 at 10:33:23AM -0800, Bob Armstrong wrote:
> >Ethan Dicks [ethan.dicks at usap.gov] wrote:
> >Thanks for any nudges towards a solution.
> 
>   Implementing the combinatorial logic for a seven segment decoder is
> trivial even for the simplest GAL.  But, as somebody else pointed out, the
> latches in a simple GAL are permanently tied to output pins, so a 4 bit
> counter plus a seven segment decoder would need 4+7=11 output pins.  A 16V8
> has only 8 outputs, and a 22V10 has only 10, which rules both of them out.

Right.
 
>   Now if you only wanted it to latch the data rather than count, that'd be
> possible with a 16V8.

I could get away with an external counter easily enough, but I was
musing aloud about a way to cut the part-count in half.
 
>   Hmm...  Having said all that, it might be possible to put a state machine
> into a 16V8 that had a 7 bit current state and a next state function that
> corresponded to "counting" is seven segments.  In theory that'd work, but I
> don't know off hand if there are enough terms inside a 16V8 to implement
> that next state function.  I'll leave that as an exercise for the reader :-)

Indeed.  Someone else already made that suggestion, and I'm thinking
about it.  The good news is that it's easy to prototype one up and
see how it works on a breadboard.

>   Another thing to keep in mind is that parts like these are really power
> hungry, even compared with traditional 74xx parts.

True.  Power is not really an issue here.  The LEDs are going to pull
a fair amount of power on their own, not including counting and driving.
 
>   Are you back down there again??  Did you see the NBC news team that
> visited a few weeks ago?

Yep... I arrived back here about 5 weeks ago.  I did see the NBC crew
on their brief stop-over, including Ann Curry making a bit of fun of
our soft-serve ice-cream machine (they arrived around 01:00 and departed
around 03:00, and I happened to be up when they arrived).

-ethan

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Ethan.Dicks at usap.gov            http://penguincentral.com/penguincentral.html