CPLD computing

From: Ben Franchuk <bfranchuk_at_jetnet.ab.ca>
Date: Tue Apr 16 16:52:35 2002

Richard Erlacher wrote:

> > OK, but that's still not enough to generate _all_ possible functions.
> >
> I'm getting really curious what sort of function one could NEED that requires
> a set of more than 64 products of those 42 inputs, though you can certainly
> use more than that by combining sums if you do need.

Carry logic found in adders can use up a lot of terms if one is not

> I think that's why this argument has persisted for so long. With programmable
> devices, I can build what I want. With TTL SSI/MSI/LSI you can build what you
> want. We could switch roles, but the fact remains, each approach has
> advantages. I just believe that the advantages of the SSI/MSI/LSI approach
> are diminshing, while the programmable logic approach continues to expand.
But the programmable logic setup is still a mess. I have yet find a
CLEAN hardware description language that is portable, simple and free.

> If you were ever to want to investigate, thoroughly, at least as thoroughly as
> you could by building such a thing, a system that required such a complicated
> logic function, with as many as 56 ORs of products with 1..20 ANDed inputs,
> you would likely start with a simulator and not with hardware.

I tend to work bottom up. I start with REAL hardware and build up.

> You'd then
> write a top-level functinoal simulation program and then test it with a sample
> program. (snip)
Testing is good. How ever it still needs to fit in the hardware.

> Doesn't this seem less spainful than (a) finding a set of bare wire-wrap
> boards, (b) installing sockets, (c) working out a large schematic design, (d)
> acquiring the long list of parts, only some of which you'll already have,(e)
> integrating the various modules you fabricate and test separately, (f) finding
> the problems and going on only when there don't appear to be any more (else go
> to (C)...) (g) and then, finally, going to the step at which you'd have
> arrived without ever fiddling with any hardware with the former approach? You
> don't really EVER have to implement anything in programmable logic unless you
> want to, but you can use all the tools to support a development in

But debuging TTL is visible. You put a logic probe on the output and
test data in. I favor switches and lights.It is not that I don't like
modern software , I as design should be able to have the final say in
exactly how things are connected even if this means shooting myself in
the foot now and then.
Ben Franchuk - Dawn * 12/24 bit cpu *
Received on Tue Apr 16 2002 - 16:52:35 BST

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