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Old 05-03-2006, 02:48 AM
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Default Re: bizzare unexplained random errors w/ Lattice 4256V CPLD

on the Lattice website forums
Lattice's response was as follows:
The fact that the error happens occasionally, and doesn't happen at all
with fewer shift registers, suggests that it's either a timing issue or
a board level issue. If the error occured all of the time, or when it
went bad it stayed bad, I would agree that it could be a logic problem.
By the way, does the design occasionally not drive a bit high (a hole
in the shift sequence) or does the shift sequence get off by a clock?
Is it happening on all shift registers, or just one?

Make sure that you have set proper timing contraints for your design
and that you check the log files for violations.

Assuming the timing looks good, I'd check your board level design. Make
sure you aren't overworking the outputs, take a look at page 20 of the
datasheet. Keep in mind that if you are driving many loads all at once
you can create ground bounce significant enough to affect the part. You
might try different input patterns to see if this changes things (use a
pattern that generates less toggling of the outputs). Also check that
you have sufficient numbers of high frequency (.1uf or .01uf) and mid
frequency (10uf to 47uf) capacitors. Check that your power supply isn't
drooping. Check that the power supply doesn't get more noisy as the
load increases.
Hope this helps!
Bart Borosky
Online Marketing Manager
Lattice Semiconductor

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