Depending on the speed have you looked at something like a 10F pic?

Forrest Christian wrote:
> I have an application where I need to end up with effectively a 24 bit 
> divide by-n counter, where n is going to be fixed at design time - 
> probably on the order of 10 million or so.   I also need to do a compare 
> on the 24 bit value to output a single bit based on the current value of 
> the divide-by-n counter. 
>
> Seems like an application for a FPGA, or perhaps the correct CPLD (if I 
> can find one which has enough flip/flops and/or logic).....  but all I 
> really need are three i/o pins,  count, reset, and "comparator output" - 
> and it seems almost impossble to find a low pin count device which has 
> enough logic inside to do a 24 bit counter without also having a huge 
> number of pins.
>
> About the only thing I've found so far are some of the Atmel ATF family, 
> which are available in 40 or 44 pin packages, which is a bit big, and 
> perhaps the Cypress PSoC which might just do the trick.   The problem 
> I'm finding with the CPLD's in particular is that there seems to be some 
> sort of unwritten rule that the flip-flop must connect directly to the 
> output pin, and you can't have extra flip-flops floating around not 
> associated with a pin.   As a result, a CPLD which implements a 24 bit 
> counter, plus an additional output must have at least 25 output pins, 
> plus 2 input pins.   Unfortunately, these seem to be few and far between.
>
> The FPGA's are just big, and most need config flash as well.
>
> I really would like to find something which is like a simple 16v8, but 
> has quite a few extra macrocells which are internal to the part which 
> are tied into the and array and not dedicated to a pin.  That way you 
> could implement a counter or similar which is much wider than the 
> device's I/O, and which doesn't require some horrific quantity of pins 
> simply to get the amount of logic needed.
>
> So, have I missed any parts?
>
> -forrest
>   


-- 

Vapour Forge

Jake Anderson

Project Manager

Mobile:       0412 897 125

Email:         jake@vapourforge.com

Web Page:  www.vapourforge.com

Your source for custom IT services

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist