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AR# 21406

7.1i SP2 MAP - "WARNING:PhysDesignRules:739 - Unexpected DCM feedback loop. The signal..."


General Description: 

When running 7.1i MAP on a design with a DCM core, you might receive the following warning: 


"WARNING:PhysDesignRules:739 - Unexpected DCM feedback loop. The signal U1_CLKFB_IBUFG on the CLKFB pin of comp DCM_INST1 is not driven by an IOB or BUFGMUX; therefore, the phase relationship of output clocks to CLKIN cannot be guaranteed." 


Note that this warning has also occurred when running BitGen.


This warning can be safely ignored in 7.1i. The warning will be removed in the next major release of the ISE software due out before the end of 2005.

AR# 21406
Date Created 09/04/2007
Last Updated 05/19/2014
Status Archive
Type General Article