What is the "Factory_JF" factor on a CLKDLL?
The "Factory_JF" value affects the jitter filter characteristic of the CLKDLL element. This attribute controls the DCM tap update rate.
If your design requires the use of a regular CLKDLL, the JF value setting is "0xC080".
If your design requires the use of a high-frequency CLKDLL or CLKDLLHF, the value setting is "0xFFF0".
These values are default settings, and you should not attempt to change them unless it is otherwise recommended. Please see (Xilinx Answer 13756) for more information.