We have detected your current browser version is not the latest one. Xilinx.com uses the latest web technologies to bring you the best online experience possible. Please upgrade to a Xilinx.com supported browser:Chrome, Firefox, Internet Explorer 11, Safari. Thank you!

AR# 25200

Virtex-5 DCM - DCM does not function correctly if CLKFB is unused and grounded or tied high


When CLKFB is unused in a Virtex-5 design containing DCMs, the pin can be tied high, grounded, or left unconnected (Verilog designs only). When CLKFB is tied high or grounded, the DCM might not lock and does not function correctly.


When the CLKFB is unused on a DCM component, use Verilog for the DCM instantiation and leave the pin unconnected.

This issue will be addressed in the ISE 9.2i design tools so that you will be able to tie CLKFB high or low when it is unused.

AR# 25200
Date Created 09/04/2007
Last Updated 12/15/2012
Status Active
Type General Article