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AR# 63076

CRITICAL WARNING: [Timing 38-282] reported when GT reference clock is set to 820MHz for -1/-2 speedgrades


The GTH datasheet specification (DS183) for maximum reference clock frequency is 820 MHz for all speed grades.

However, ISE and Vivado speed files are speed grade specific and restrict reference clock frequencies to less than 820 MHz for -2 and -1 devices. 

This causes min_period violations if external reference clock sources are used that exceed the speed-file limits for -1 and -2 devices.


The min_period violation for the REFCLK can be ignored as long as the REFCLK constraint does not exceed 820 MHz.

Revision History:
12/10/2014 - Initial Release
AR# 63076
Date Created 12/09/2014
Last Updated 12/22/2014
Status Active
Type General Article
  • Virtex-7