Constraints Editor
Initializing Flip-flops and Latches
You can use the FFS/LATCH Initialization dialog box to initialize flip-flops and latches. This sets the initial value (0 or 1) for the selected flip-flops or latches.
Use the INIT constraint sparingly. Initialization should be handled as part of the HDL code whenever possible.
To Initialize Flip-flops or Latches
  1.  Open the FFS/LATCH Initialization dialog box.
  2.  To limit the registers (flip-flops or latches) listed in the Available list, enter a filter string in the Filter box and click Find. For example, to list only registers containing the string "ffout," type *ffout* in the Filter box. The filter is not case sensitive.
  3.  In the Comment box, enter a comment for this initialization entry.
  4.  In the Init Value box, enter the initial value for the selected registers.
  5.  In the Available list, select the registers to initialize.
  6.  Click Add to move the selected names to the Register Targets list.
Initializing flip-flops and latches creates an INIT constraint. The new constraint appears in the current Workspace table.
For more information about this constraint, see the Constraints Guide in the online document collection.
See Also

Copyright © 2008, Xilinx® Inc. All rights reserved.