On Sat, Mar 5, 2011 at 4:31 AM, Oli Glaser wrote: > 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 o= n > 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 > switches in between. This means you can set them up to perform all sorts > 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 change= d. > > > 3. Why are they used? > > They are very versatile and fast. For example a design I am prototyping > reads ADCs at >400Msps (400MBps) which an FPGA is used for (try doing > that with a PIC) > Sometimes maybe you just need a small PLD for "glue" logic (see recent > post on CPLD) or similar (and there is no standard logic solution > available) > I believe they are also used during the development of ASICs to speed up > design/testing/debugging (much cheaper than actually making the chips > then finding a problem) > > > > 4. How are they used? > > 5. I've seen the term "parallel processing" mentioned a lot. How does > this > > tie in with PAL/CPLD/FPGA? > > It's easy to do many things in parallel, since you are in control of how > wide the bus is and the logic. Say you had a very complex mathematical > operation that needs to happen very quickly - you can optimise (the > whole chip if necessary) completely *just* for that operation, as > opposed to a general purpose uC which needs to be able to do lots of > other things too (a uC that could only perform 1 instruction would be > 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 > PIC32, > > 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 - > copies of the Xilinx, Altera for a lot less) but getting up to speed is > harder than with uCs (less online info/forums etc) I think due to them > having far less hobbyist/small company use. > I actually designed my own dev board to start with, as I thought it > would be a good way to learn about how everything worked - which it was > (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 > from > > 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, > couple I can remember reading - "A design warriors guide to FPGAs" (I > think that's right) "FPGA proptoyping with Verilog examples" (uses a > cheapish Xilinx board if you can get hold of it still - eBay..) "Verilog > - a guide to digital design and synthesis" > > See what other books are out there, should be some decent (new) ones > available. Thanks for the detailed reply, Oli. 1. To start off with basic things (hobby use, but with potential to do craz= y things like reading at 400M samples/s), which would you recommend, PAL, CPLD, or FPGA? 2. How is "speed" actually rated for these types of devices? Clock speed? I= f so, what is the clock speed generally around? Without even thinking, I woul= d assume reading at 400M samples/s would require at least 400 MHz. Do these things use crystals as a clock source? --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .