To define a differential pin pair in an I/O planning project:
- In the I/O Ports window, select any two I/O ports, right-click,
and select Make Diff Pair.Important: The Make Diff Pair option is not available in RTL projects. In RTL projects, differential ports must be defined in the source code using appropriate I/O buffer instantiations.
In the Make I/O Diff Pair dialog box (see the following figure), the two I/O Ports display with Positive End and Negative End assignments made by the tool.
- To reverse the Positive End and Negative End signals, click
Swap, and click OK.Tip: Right-click, and select Split Diff Pair to separate a diff pair into two ports.Important: When you apply certain constraints to one side of a differential pin pair in an UltraScale™ architecture, the opposite constraint is automatically applied to the other side. For example, if you apply a PULLDOWN constraint to the P side, a PULLUP constraint is applied to the N side. If you make changes to the constraints, the most recent settings overwrite previous settings.