Keywords: ECS, CLKIN_PERIOD, Project Navigator
When I use the schematic capture tool to add a value to the PLL attribute CLKIN_PERIOD in ECS, a message reports:
"'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 the 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;