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AR# 13815

Virtex-II DCM - The CLKFX output stops; DCM is LOCKED for a short time, then unlocks

Description

The CLKFX output does not work in my design.

The M and D values are within specifications, as is the jitter measurement; however, CLKFX never locks. It will toggle at first, but will then stop. The LOCKED output will go High, then falls Low within several cycles.

Solution

This is a known issue. When CLKFX is used, the CLKIN_PERIOD attribute must be set. If this attribute is not set, one of the bit settings for DCM will not be correctly set in Bit Generator.

Be sure to set the CLKIN_PERIOD attribute with the correct period (in ns).

AR# 13815
Date Created 08/29/2007
Last Updated 12/15/2012
Status Active
Type General Article