On Mon, 29 Jan 2007 22:20:28 -0700, you wrote:

>Paul Anderson wrote:
>
>>Here's a pretty basic question for the list.  What is the difference
>>between an FPGA and a CPLD?
>>  
>>
>That's a hard question to answer since the line is becoming more and 
>more blurred (see the MachXO we were discussing earlier).  I'm also not 
>a FPGA expert by any means.
>
>FPGA=Lots of gates-10K on up, millions is not uncommon.   Typically but 
>not always volatile - I.E. needs external flash to load it's "program", 
>which takes a bit (not immediate on).
>
>CPLD= typically onboard flash, immediate startup, relatively small 
>numbers of gates  (1000 is pretty typical).
>
>Generally, a FPGA has enough gates that you can implement an entire 
>system in it.   Many FPGA manufacturers now have entire software 
>microprocessor cores which run within the FPGA itself, where a typical 
>CPLD is useful for glue only.
>
>CPLDs seem to also have a more ridgid internal structure, whereas the 
>FPGA is more flexible in it's signal routing internally.
>
>Not sure if this helps but I really typically think of the CPLD as a PAL 
>on steroids, and the FPGA as a programmable ASIC.
>
>The MachXO I mentioned is one of those beasts where you can really think 
>of it as a small FPGA with the cost and nonvolatility benefits of a CPLD.
>
>-forrest

Another common comparison is 'granularity' - an FPGA is closer to a sea of gates, with each gate
being fairly simple , e.g. a 4-input lookup table or single register..
CPLDs typically contain a number of more complex macrocells - typically one or 2 registers with
various internal routing options, with programmable interconnect between them.

Larger FPGAs also often contain blocks of RAM - often dual-port, plus other useful blocks like
multipliers. 


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