GAL16V8 as a modern substitute for a 7447?
ethan.dicks at usap.gov
Sat Dec 8 12:41:43 CST 2007
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.
> 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 Dicks, A-333-S Current South Pole Weather at 8-Dec-2007 at 18:30 Z
South Pole Station
PSC 468 Box 400 Temp -25.2 F (-31.8 C) Windchill -53.8 F (-47.6 C)
APO AP 96598 Wind 15.5 kts Grid 12 Barometer 678.3 mb (10692 ft)
Ethan.Dicks at usap.gov http://penguincentral.com/penguincentral.html
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