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AR# 29596

9.2i MAP - DIFF_TERM attribute dropped during MAP when IBUFDS_DIFF_OUT primitive is used in a submodule of a design


When I use the IBUFDS_DIFF_OUT primitive in a submodule of my design with a DIFF_TERM attribute, the attribute is dropped by MAP. This issue occurs when using Virtex-4 and Virtex-5 devices.

I checked the PAD report and the DIFF_TERM attribute is not there on the pins specified. Why does this occur?


This issue occurs because MAP drops the DIFF_TERM attribute on a IBUFDS_DIFF_OUT primitive when hierarchy is retained. Consequently, the attribute is not included in the PAD report. This issue will be fixed in a future software version.

You can work around this issue by enabling the "Allow Logic Optimization Across Hierarchy" option in MAP. When using the command line, set the -ignore_keep_hierarchy.

Another way to work around this issue is to set the environment variable as follows:



Linux and Solaris


For general information on setting ISE environment variables, see (Xilinx Answer 11630).

AR# 29596
Date Created 10/28/2007
Last Updated 12/15/2012
Status Active
Type General Article