When I change the attributes for the differential I/O (e.g., slew rate, IOStandard, etc.) in the PlanAhead software, the ".ucf" file that is written out only writes out the attributes for the P side.
Why is the N side of the differential pair being ignored?
This is a known issue in the PlanAhead software.When you make changes to the attributes for a differential I/O, the changes are only reflected for the P side of the differential pair (rather than the N side).
You can work around the issue by manually writing out the attributes for the N side in the ".ucf" file.
You can also leave it as it is and the implementation tools will take care of assigning location and attributes of the N side of the pair depending on the location and attributes of the P-side.
A CR is under investigation to fix the issue for a future release of thePlanAhead software.