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AR# 18722

10.1 Floorplanner - Nets (ratsnest) from differential IOB not showing up in GUI

Description

I have a differential input in my design that connects to FFs. However, when I look at the design in Floorplanner, I see only a connection from the P-side of the differential pair to the N-side. I cannot see the connection to the FF.  

 

In the same design, I can see the nets connected to the logic from another differential IOB. I verified in the FPGA Editor that all connections do exist. Why are these not visible in Floorplanner?

Solution

In this case, the difference between the two differential pairs is that one has a local buffer between the pad and the FF that it drives. Since Floorplanner does not perform any buffer pushing, the connection is lost. The connection exists; however, it cannot be seen in Floorplanner.

AR# 18722
Date Created 09/03/2007
Last Updated 05/16/2014
Status Archive
Type General Article