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DP83869HM: Do we need to swap lines on transmit and receive for bridge mode?

Jon Kreger
Prodigy 10 points

Part Number: DP83869HM
Other Parts Discussed in Thread: DP83869

Hi,

There is a noted confusion/discrepancy in TI documentation for DP83869.

The datasheet lists Tx (RGMii) as being an input to the part and Rx as being an output;

however, the description (pg 37) says that the pins are reversed for bridge mode.

It says that Tx behaves as an input pin and Rx behaves as an output pin, which

are the same descriptions for normal operation as listed in the pinout definitions.

We have Rx going to Rx on the switch and Tx going to Tx on the switch. Is this the correct

connection?  Or based on the reversal of pins, do we swap line, so that we have Tx from

switch going to Rx on the bridge and Tx on bridge going to Rx on switch?


Please see the block diagram below.

  • 0
    TI__Expert 5670 points
    Hi Jon,

    My understanding is that there is no swapping for RGMII TX and RX in bridge mode. It's probably just the definition of TX and RX with respect to the MAC.

    I will double check and get back to you on this.

    Regards,

    Hung Nguyen
  • 0 in reply to Hung Nguyen92
    TI__Expert 5670 points
    Hi Jon,

    It is confirmed that the swapping is only for definition with respect to the MAC. There is NO physical swapping between TX and RX pin for RGMII interface.

    Per standard:
    (1) RGMII definition on the PHY
    - TX pins are input pins
    - RX pins are output pins

    (2) RGMII definition on the MAC
    - TX pins are output pins
    - RX pins are input pins

    When DP83869 is configured into SGMII-to-RGMII bridge mode, the device acts as RGMII MAC. However, the direction of RGMII pins remain the same (TX pin = input; RX pin = output), as defined in the pin table of the datasheet.

    As the result, there is a note on page 37 stating the reverse in the pin definition to be consistent with (2).

    As long as you follow the pin I/O direction in the pin table when connecting DP83869 to another device, it shouldn't be a problem.

    Regards,

    Hung Nguyen