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AR# 21436

Virtex-4 RocketIO - Why does RocketIO Wizard generate different attribute values for clocking as compared to the Clocking Decision Tree in the RocketIO User Guide?

Description

General Description:  

Some attributes in the RocketIO Wizard such as RXCLKMODE, RXASYNCDIV, TXCLKMODE, and TXASYNCDIV are different from those in the Clocking Decision Flow shown in the User Guide.

Solution

There are multiple combinations that build one divide ratio. Although the values are different, the final divider ratio will be same. For example, in the picture, there are two combinations that achieve divide by 20. The red line passes the top dividers /4 and /5, which are the synchronous dividers. Also, the blue line passes the bottom dividers /4 and /5, which are the asynchronous dividers. 

 

Dividers in receiver
Dividers in receiver
 

 

For details about the Receive Clocking Decision Flow or the Transmit Clock Decision Flow, please see the RocketIO User Guide: 

http://www.xilinx.com/xlnx/xweb/xil_publications_index.jsp?category=User+Guides

AR# 21436
Date Created 09/04/2007
Last Updated 05/19/2014
Status Archive
Type General Article