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AR# 46614

Kintex-7 FPGA KC705 Evaluation Kit - Usage of GTX TX / RX Polarity Controls on SFP/SFP+ interface

Description

SFP/SFP+ designs using the Kintex-7 FPGA KC705 Evaluation Kit Rev 1.0 boards can used the FPGA transceiver TX and RX polarity control attributes to undo the SFP/SFP+ interface P, N pin swaps.

Solution

On the Rev 1.0 version of the KC705 board, the FPGA SFP/SFP+ transmitter signals MGTXTXP2 and MGTXTXN2 are swapped.The SFP/SFP+ receiver signals MGTXRXP2 and MGTXRXN2 are also swapped.

Loopback:

SFP/SFP+ Loopback tests or connections to another Rev 1.0 KC705 board work successfully with or without changing the TX and RX polarity control.

Transmitting:

When designing with the KC705 SFP/SFP+ transmitter (MGTXTXP2, MGTXTXN2) interface, the FPGA's GTX TX polarity control should be used to change polarity and compensate for the transmitter's MGTXTXP2, MGTXTXN2 pin swap. No other changes are required for normal operation.

Definition of TX polarity control from the 7 Series Transceiver User Guide is repeated below:
http://www.xilinx.com/support/documentation/user_guides/ug476_7Series_Transceivers.pdf

TX Polarity Control
Functional Description
If TXP and TXN differential traces are accidentally swapped on the PCB, the differential data transmitted by the GTXtransceiver TX is reversed.One solution is to invert theparallel data before serialization and transmission to offsetthe reversed polarity on the differential pair.The TX polarity control can be accessed through the TXPOLARITY input from the fabric user interface. It is driven High to invert the polarity of outgoing data.

Receiving:

Likewise, when receiving a signal on the KC705 SFP/SFP+ receiver (MGTXRXP2, MGTXRXN2) the FPGA's GTX RX polarity control should be used to change polarity and compensate for the receiver's MGTXRXP2, MGTXRXN2 pin swap. No other changes are required for normal operation.

Definition of RX polarity control from the 7 Series Transceiver User Guide is repeated below:
http://www.xilinx.com/support/documentation/user_guides/ug476_7Series_Transceivers.pdf

RX Polarity Control
Functional Description
If RXP and RXN differential traces are accidentally swapped on the PCB, the differential data received by the GTXtransceiver RX are reversed. The GTX transceiver RX allows inversion to be done on parallel bytes in the PCS afterthe SIPO to offset reversed polarityon differential pair. Polarity control function uses the RXPOLARITY input, whichis drivenHigh from the fabric user interface to invert the polarity.

Linked Answer Records

Master Answer Records

Answer Number Answer Title Version Found Version Resolved
45934 Kintex-7 FPGA KC705 Evaluation Kit - Known Issues and Release Notes Master Answer Record N/A N/A

Associated Answer Records

AR# 46614
Date Created 03/08/2012
Last Updated 02/12/2013
Status Active
Type General Article
Boards & Kits
  • Kintex-7 FPGA KC705 Evaluation Kit