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# 31703

ML405 - TX_Disable input to SFP module can be driven to undefined state


A problem with the ML405 SFP TX Disable circuit has been identified. The SFP/MSA specification states that all SFP modules have an internal 4.7K PullUp on the SFP TX Disable pin. The resistor, R320, on the ML405 board acts as a PullDown on the SFP TX Disable pin external to the SFP module. Since there is already a 4.7K PullUp inside the SFP and a 4.7K PullDown external to the SFP TX Disable pin, this causes 1.65V to be applied to the TX_DISABLE pin which is an undefined logic state.


To work around this issue, replace R320 with a 1K ohm 0603 resistor to remove the potential for an undefined logic state on the SFP TX Disable pin.

1. R320 is located on the bottom side of the board (near the back side of the SFP cage).

2. Below is an image of the Bottom Side of ML405 board. R320 is highlighted Red. Replace with 1K ohm 0603 resistor.

Top Left of the Bottom Side of the ML405 board
Top Left of the Bottom Side of the ML405 board

AR# 31703
Date Created 09/17/2008
Last Updated 12/15/2012
Status Active
Type General Article