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AR# 19444

6.2i Timing/PAR - Incorrectly receiving "WARNING:Timing:2796 (maximum frequency)" on my DCM


General Description:

When I run through PAR or do a static timing analysis (Timing Analyzer or TRCE) on my design, I receive the following warning:

"WARNING:Timing:2796 - The input clock CLKIN_IBUFG_OUT_OBUF to DCM

instance_name_DCM_INST has a period (frequency) specification of 2564 ps

(390.02 Mhz). This violates the minimum period (maximum frequency) of 3124 ps

(320.10 Mhz)."

However, the data sheet states that using the DLL outputs only (CLK0, CLK180, etc.) the maximum frequency, up to 420 MHz, for Virtex-II.


If you are only using the DLL outputs of the DCM, you can safely ignore this warning. The cause of this problem is the setting the DFS_FREQUENCY_MODE. If you are not using any DFS outputs (CLKFX and CLKFX180), but the DFS_FREQUENCY_MODE is set to either HIGH or LOW, then you will get this warning.

You can get rid of this false warning by changing the value of DFS_FREQUENCY_MODE from HIGH to LOW or #OFF.

AR# 19444
Date 01/18/2010
Status Archive
Type General Article