6.1i, Architecture Wizard, DCM - "ERROR: Only Low Frequency mode is valid for Cascading in Series. Please enter an Input Clock Frequency value within the valid Low Frequency Range..."
Description
Keywords: Clocking, 2X, cascade, CLK2X
Urgency: Standard
General Description:
I am using the DCM Wizard to create a cascaded DCM using CLK2X. When I enter 30MHz as the input frequency, the following error occurs:
"Only Low Frequency mode is valid for Cascading in Series. Please enter an Input Clock Frequency value within the valid Low Frequency Range. Low Frequency Mode: 24 - 90 MHz."
The frequency entered is within the range specified in the error message. Why did I receive this error?
Solution
The Wizard did not check the frequency range correctly.This problem has been fixed in the latest 6.2i Service Pack available at:
http://support.xilinx.com/xlnx/xil_sw_updates_home.jsp
The first service pack containing the fix is 6.2i Service Pack 2.
NOTE: The DRC itself is correct (i.e., cascading DCM is limited in the low-frequency range).
For more information, refer to (Xilinx Answer 18181).