GAL16V8 as a modern substitute for a 7447?

[Tony Duell]

> 
> Hi, all,
> 
> Has anyone here worked with or ever plotted silently to create a moderish
> 7-segment decoder/driver from a GAL16V8?  I'm working on a project made
> from classic parts, and am trying to reduce part count rather aggresively,
> since I'm going to hand-wire it.
> 
> One thought was to attempt to combine a 7490 _and_ a 7447 in a single
> GAL16V8.  I have blown hundreds of PALs, but have much less experience
> in designing with them, so I'm not even sure that it's possible to mash
> together that much logic internally in a 16V8.  I know all the outputs
> are optionally registered, so presuming one has 4 assignable flip-flops,
> one could theoretically make a counter on the output pins, but what's
> less clear to me is if you could then take those terms and internally
> decode them to a 7-segment display.

I'm pretty sure you can't.

Yes, you can sue 4 of the flip-flips to make a counter (although with a 
common clock input, you would have to make a synchronous counter, and 
I've not worked out if you have enough product terms to do that, I think 
you do, thought). But those 4 flip-flops take up 4 of the 8 outputs of 
your GAL. 

Yes, you can use feedback terms to process the otuputs of that counter. 
But you only havr 4 outputs left, and you need 7 for drive a 7-segment 
display.

What I've not workeod out if you can do (and I suspect you don't ahve 
enough product terms to do it) is to make a state machine with 7 
flip-flops, the 10 allowed states of which are the 7 segment patterns, 
and a trasnition table something like : 
1111110 -> 0110000 -> 1101101 etc
  0          1           2  (7 segemnt patterns)

I suepect you don't have enough product terms to do that, but I have not 
tried to work it out.

-tony