Answers Database

M1.3 4kex Timing - Long delays are calculated for TBUFs driving long lines with Pullups.


Record #2741

Product Family:  Software

Product Line:  FPGA Core

Problem Title:
M1.3 4kex Timing - Long delays are calculated for TBUFs driving long
lines with Pullups.



Problem Description:
A long delay is calculated for TBUFs driving long lines
with pullups in XC4000EX devices. This is because the tools
are incorrectly defaulting to wired delays when a pullup
is present, rather than the active delay.

Reference # 100471


Solution 1:

Pullups are not recommended for use with active TBUFs because
of the existance of weak keepers on the long lines.



End of Record #2741