8 Dec
2007
8 Dec
'07
3:01 p.m.
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