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AR# 23829

8.2i NGDBuild - WARNING:ConstraintSystem:11 -In file: signalconversion.ucf(2): Loading' DIFF_TERM'constraint from file is not supported at this time

Description

I have a design that uses on-chip LVDS differential termination. The Virtex-4 User's Guide states that I should use the DIFF_TERM attribute to achieve this. When I do that, however, I receive the following error:

"WARNING:ConstraintSystem:11 - In file: signalconversion.ucf(2): Loading a 'DIFF_TERM' constraint from file is not supported at this time. This constraint specification will be ignored."

This appears to be a major issue because I NEED the differential termination.

A sample section from my UCF file is:

NET "adcIn_N<0>" LOC = "D17" | IOSTANDARD = LVDS_25 | DIFF_TERM="TRUE";

NET "adcIn_P<0>" LOC = "C17" | IOSTANDARD = LVDS_25 | DIFF_TERM="TRUE";

How do I use the DIFF_TERM?

Solution

The DIFF_TERM is not allowed to be used in UCF now. Try to instance IBUFDSand add attribute in the code other than use UCF. For example:

IBUFDS #(

.DIFF_TERM("FALSE"), // Differential Termination (Virtex-4 only)

.IOSTANDARD("DEFAULT") // Specify the input I/O standard

) IBUFDS_inst (

.O(O), // Clock buffer output

.I(I), // Diff_p clock buffer input (connect directly to top-level port)

.IB(IB) // Diff_n clock buffer input (connect directly to top-level port)

);

// End of IBUFDS_inst instantiation

Please refer to the Library Guide or (Xilinx Answer 23579) for more Information.

AR# 23829
Date Created 09/04/2007
Last Updated 12/15/2012
Status Active
Type General Article