AR# 18791

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Virtex-II/Pro, DCM - What is the input duty cycle requirement when using CLKIN_DIVIDE_BY_2 attribute?

Description

Is there a duty cycle requirement for the input clock when using the CLKIN_DIVIDE_BY_2 attribute?

Solution

Yes, there is a duty cycle requirement for the input clock.

When you use the CLKIN_DIVIDE_BY_2 attribute with the DCM, the duty cycle requirement depends on the input clock frequency.

Frequency Less than 400 MHz

For Virtex-II and Virtex-II Pro:

Use the Input Clock Low/High Pulse Width numbers.

For Virtex-4 and Virtex-5:

Use the Input Clock Duty Cycle Tolerance numbers.

These numbers are specified in the DC and Switching Characteristics section of the data sheet for the device family.

http://www.xilinx.com/support/documentation/index.htm

Frequency greater than 400 MHz

The duty cycle should be 45/55 to 55/45.

AR# 18791
Date 12/15/2012
Status Active
Type General Article
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