2 Replies Latest reply on Mar 14, 2017 12:35 PM by nomac_2263406

    USB 3.0 RX TX pin swapping



      I am laying out a FX3 USB 3.0 board with a USB Type A . connector. To avoid USB signal overlapping, I would like to swap the TX+ and TX- signals. My question is, can I swap only the TX+ and TX- signals without swapping the RX+ and RX- signals ? In other words, can i reverse the polarity of only one differential pair without reversing the polarity on another differential pair?




      The application note AN70707 mentions that polarity swapping is doable but doesn't go in detail of possible swap combinations..




      I was also reading online that TX+/TX- can be swapped with RX+/RX- signals as well. Is it true for FX3? I have to use USB Type A connector. If this swapping of RX signals with TX signals is possible then it will simplify the design by allowing me to put the USB connector on the other side of the board and avoiding vias in USB signals.




      Thanks in advance.

        • 1. Re: USB 3.0 RX TX pin swapping

          The USB 3.0 spec is allowed to connect SS_TX_M  and SS_TX_P of FX3 (any super speed device) to SS_TX_P and SS_TX_M of the connector respectively. It is also applicable for SS_RX pins.


          It is not necessary to swap SS_RX signals, if you want swap only SS_TX signals.


          Note that there is no such swapping (D+/ D-) feasibility in USB 2.0. We must connect D+ to DP and D- to DM.


          Please refer the connections of USB 3.0 lines on CYUSB3KIT-001 DVK in the embedded image. It shows the swapping SS_RX lines on the connector side.



          Note that you must not connect TX+/TX- with RX+/RX-.


          • 2. Re: USB 3.0 RX TX pin swapping

            Thanks for the Clarification.


            You guys are always very responsive!