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AR# 23153

Spartan-3E - Changes to fixed phase shift in ISE 8.1i Service Pack 3

Description

Starting in the ISE design tools 8.1i Service Pack 3, the fixed phase shift operation for the Spartan-3E DCM has changed.

Solution

The original fixed phase shift specification allowed you to phase shift up only to +/- 180 degrees over +/-255 phase shift increments. For example, a fixed phase shift of +255 would shift the output clock +180 degrees.

Starting in 8.1.03i, the fixed phase shift operation changed so that you can phase shift up to +/-360 degrees over +/-255 phase shift increments. For example, a fixed phase shift of +255 will shift the output clock +360 degrees. This is the same fixed phase shift functionality of Spartan-3.

If you have been using the fixed phase shift operation for Spartan-3E prior to ISE 8.1.03i, you can simply divide your fixed phase shift setting by two to get the equivalent phase shift in 8.1.03i. For example, a fixed phase shift setting +128 will phase shift the DCM output clock by 90 degrees in ISE 8.1.02i and earlier. In 8.1.03i, a fixed phase shift setting of 64 will shift the DCM output clock by 90 degrees.

For more information on how the fixed phase shift operation works in Spartan-3E, see the Spartan-3 Generation FPGA User Guide at:

http://direct.xilinx.com/bvdocs/userguides/ug331.pdf

Also, for more information on the variable phase shift operation in Spartan-3E, see (Xilinx Answer 23004) and (Xilinx Answer 22414).

AR# 23153
Date Created 09/04/2007
Last Updated 12/15/2012
Status Active
Type General Article