UPGRADE YOUR BROWSER

We have detected your current browser version is not the latest one. Xilinx.com uses the latest web technologies to bring you the best online experience possible. Please upgrade to a Xilinx.com supported browser:Chrome, Firefox, Internet Explorer 11, Safari. Thank you!

AR# 23612

Embedded Tri-mode Ethernet MAC Wrapper v4.1 - How can I switch to 250 MHz reference clock to avoid jitter problems

Description

Virtex-4 FX GT11 jitter errata exceeds the IEEE Std 802.3-2002 specification when using a reference clock of 125 MHz. To improve the jitter performance of the transmitted serial line, Xilinx recommends a 250 MHz reference clock. For more information, see the Virtex-4 FX errata at:

http://xwebpub/xlnx/xweb/xil_publications_display.jsp?category=Errata&iLanguageID=1

Solution

Use the following information to switch between reference clock frequencies of 250 MHz and 125 MHz.

250 MHz

GT11 Attributes:

TXOUTDIV2SEL = 4

TXPLLNDIVSEL = 10

RXOUTDIV2SEL = 1

RXPLLNDIVSEL = 20

DCM attribute to divide down reference clock to 125 MHz:

CLKIN_DIVIDE_BY_2 = TRUE

125 MHz

TXOUTDIV2SEL = 4

TXPLLNDIVSEL = 20

RXOUTDIV2SEL = 1

RXPLLNDIVSEL = 40

The clocking will be updated to use a 250 MHz reference clock for the GT11 and use the internal clock dividers in Embedded Tri-mode Ethernet MAC Wrapper v4.2 Core available in 8.2i IP Update 1, scheduled for release in July 2006.

AR# 23612
Date Created 09/04/2007
Last Updated 12/15/2012
Status Active
Type General Article