On 05/03/2011 07:36, V G wrote:
> Just out of curiosity.
>
> I've been reading the wikipedia pages, as well as some other websites on =
the
> topic of PAL/CPLD/FPGA, but I still don't understand the following:

I'll give a few of these a go... :-)

> 1. What are they?

Very roughly, they are just a load of logic gates with programmable=20
switches in between. This means you can set them up to perform all sorts=20
of different functions (by "wiring" the gates together as you like)
  Kind of like designing your own chip.

> 2. How do they work?

After programming, like any other digital chip, except they can be changed.

> 3. Why are they used?

They are very versatile and fast. For example a design I am prototyping=20
reads ADCs at >400Msps (400MBps) which an FPGA is used for (try doing=20
that with a PIC)
Sometimes maybe you just need a small PLD for "glue" logic (see recent=20
post on CPLD) or similar (and there is no standard logic solution=20
available)
I believe they are also used during the development of ASICs to speed up=20
design/testing/debugging (much cheaper than actually making the chips=20
then finding a problem)


> 4. How are they used?
> 5. I've seen the term "parallel processing" mentioned a lot. How does thi=
s
> tie in with PAL/CPLD/FPGA?

It's easy to do many things in parallel, since you are in control of how=20
wide the bus is and the logic. Say you had a very complex mathematical=20
operation that needs to happen very quickly - you can optimise (the=20
whole chip if necessary) completely *just* for that operation, as=20
opposed to a general purpose uC which needs to be able to do lots of=20
other things too (a uC that could only perform 1 instruction would be=20
pretty useless)

> 6. What is the difference between PAL, CPLD, and FPGA and under what
> circumstances would you use each of them in?
> 7. Why not use a microcontroller such a PIC to do the work?
> 8. How does each one of them compare to a microcontroller, let's say PIC3=
2,
> in terms of cost, processing power, complexity, etc?
> 9. Are simple development boards for them expensive? I'm interested in
> messing around with them. How is programming done?

There are cheap dev boards and programmers floating around (eBay etc -=20
copies of the Xilinx, Altera for a lot less) but getting up to speed is=20
harder than with uCs (less online info/forums etc) I think due to them=20
having far less hobbyist/small company use.
I actually designed my own dev board to start with, as I thought it=20
would be a good way to learn about how everything worked - which it was=20
(a lot more involved though)

> I know those are a lot of questions, and *someone* is going to tell me to
> google it, but I assure you all that I have, and would prefer answers fro=
m
> human beings in this case.
>
> Humans give insight.
>
> Google does not.

Guggle is not great for FPGAs - I would grab a few books on the subject,=20
couple I can remember reading - "A design warriors guide to FPGAs" (I=20
think that's right) "FPGA proptoyping with Verilog examples" (uses a=20
cheapish Xilinx board if you can get hold of it still - eBay..) "Verilog=20
- a guide to digital design and synthesis"

See what other books are out there, should be some decent (new) ones=20
available.





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