Answers Database

M1.5 9500/XL: Fitter uses 2 macrocells instead of 1 for combinatorial latch


Record #4174

Product Family:  Software

Product Line:  EPLD Core

Problem Title:
M1.5 9500/XL: Fitter uses 2 macrocells instead of 1 for combinatorial
latch



Problem Description:
Keywords:  CPLD, Fitter, 9500, combinatorial, latch, NOREDUCE

Urgency:   Standard

General Description:
For some combinatorial feedback latches, the fitter uses 2 macrocells instead of
 1, incurring an additional macrocell feedback delay. Normally, the NOREDUCE pro
perty applied to the latches output net should identify the break point in the f
eedback loop.


Solution 1:

Workaround:
If the fitter incorrectly breaks the feedback loop in the middle of the latch (i
nstead of at the NOREDUCE net), you must apply COLLAPSE properties to the interm
ediate nets within the latch to force them into the same macrocell as the latche
s output net.



End of Record #4174