Michael Rigby-Jones wrote:
>
> > > > Hi all
> > > > Ive got a circuit design that uses 4 or 5 TTL chips to take in
> > > > 16 address lines to enable various peripherals.
> > > > Im looking to reduce the IC count to 1 chip.
> > > > Ive heard about pal,gal and pld chips but have no idea how
> > > > to use them or program them. Would these chips suit the job
> > > > and if so where do I learn about them?
> >
> > I'd use a Scenix SX18 chip. Quick, dirty, cheap.
> >
> I'd say it depends totaly on the speed of your circuit.  If this is the
> address bus of a microcontroler/microprocessor(and it sounds like it), then
> even a 50Mhz Scenix may give an unnaceptable latency.  With 16 address lines
> to read and process, I would think that you would be looking at a latency in
> the microsecond region which is way too slow unless your micro is running at
> much less than 1Mhz.  Certainly it won't come close to the speed of a GAL,
> which is in the 10's of nanoseconds range.

If you want more address lines, you can use a SX28. Each
instruction takes about 20ns, and you are in control of
what comes out the ports, so you could have a glitch-less
glue chip. I'd say a few hundreds of ns would do it.

I agree about the speed of the GAL - it is real fast. It
is just a pain in the butt (IMHO) to implement and develop
on for a beginner.

--
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