Inside Xilinx high speed transceivers, are pre and post emphasis options which can be tuned for a specific interface. How does pre and post emphasis work and how does it affect the SI on the board?
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The pre- and post-emphasis attributeshelp to open up the data eye at the down stream device. When transmitting data at high speeds across long cables, the signal integrity of the interface can degrade to a point where data recovery becomes impossible. Adjusting pre- and post-emphasis can help to open up the data eye to allow for data recovery.
The Virtex-4 MGT Users Guide (UG076:http://www.xilinx.com/support/documentation/user_guides/ug076.pdf) contains a good discussion onthe effects of pre and post emphasis in detail. Please refer to the "Output Swing and Emphasis" section of UG076 for more information.