AR# 4978


14.x Constraints - What resources should be constrained in the User Constraint File (UCF)?


What resources should be constrained in the UCF?


The following resources must be constrained in the user constraint file (UCF):

  • The internal signal for one or more clocks (PERIOD)
  • I/O speed (OFFSETS)
  • Logic-using multi-cycle clocks (FROM-TO)
  • Pin-to-pin timing (FROM PADS TO PADS)
  • Pin locations and logic locations (LOC)
  • DCM attributes (DCM...)
  • Initial values of the RAM/ROMs (INIT)

For additional information, see the Xilinx Support Web site:

For more details on timing constraints, please see the Timing Constraints User Guide:

AR# 4978
Date 12/15/2012
Status Active
Type General Article
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