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AR# 15876

9.2 Schematic Editor - When I use the schematic capture tool, I cannot assign any value other than "0" to the CLKIN_PERIOD attribute for the PLL


When I use the schematic capture tool to add a value to the PLL attribute CLKIN_PERIOD in ECS, I receive the following message: 


"'x' is not a legal value for the CLKIN_PERIOD attribute." 


The value I specified is not assigned to CLKIN_PERIOD. 

The attribute traits of CLKIN_PERIOD show that both the upper bound and lower bound are "0," and I cannot change these values.


This issue is Fixed in ISE 10.1. 


For ISE 9.2i and earlier, you can work around this problem by specifying the CLKIN_PERIOD attribute in the UCF.  


The basic UCF syntax is: 

INST "instance_name" CLKIN_PERIOD=n; 


where "n" is a floating-point number representing nanoseconds. 


The following statement specifies a 35-nanosecond period of the clock used to drive the CLKIN pin of the PLL: 

INST "top/clk_buf_name" CLKIN_PERIOD=35;

AR# 15876
Date Created 09/03/2007
Last Updated 03/05/2015
Status Active
Type General Article