On Wed, Aug 04, 1999 at 07:17:50PM +0800, Justin Grimm 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?

The manufacturers would be a good start. Lattice/Vantis,
Xylinx, Atmel, Cypress, etc. Several offer free or eval
design software. Atmel even offers a free CD (ISD 6.0) that
includes a license for the Everest synthesis software.

Also, a good portal site for programable logic is the
"Programmable Logic Jump Station" at http://www.optimagic.com

Generally, in programmable logic, there originally were PLDs,
PALs, GALs, etc -- those tend to be quite simple and limited
in function. The next step up are the CPLDs, (Complex PLDs)
which in essence amount to a whole bunch of PLDs with an
interconnect fabric. The high end devices are FPGAs, which
is undoubtedly way overkill to replace a few TTL chips;
among other things, the FGPAs have huge pin counts, and
often need external EPROM or flash ROM to boot from.
If you're using a uC with a real memory bus, Waferscale
(http://www.waferscale.com) has an interesting device
that integrates Flash memory, SRAM and a 16-cell CPLD
on the same chip.

> Also, would a pic chip be fast enough to substitute a logic
> device?
> Thanks
> Justin

I would imagine that the main concern would be latancy,
and possibly pin count.  There is actually a Microchip Ap Note
(511, at
http://www.microchip.com/10/Appnote/Category/16C5X/00511/index.htm
software at
http://www.microchip.com/10/Appnote/Category/16C5X/00511/idxZIP0.htm)
on using a PIC16C5x as a replacement for a PLD.

--Bob

--
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Bob Drzyzgula                             It's not a problem
bob@drzyzgula.org                until something bad happens
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