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HOW TO CONNECT TWO DP83620 PHYS BACk TO BACK VIA THE MII INTERFACE

WhiteHorse
Genius 4430 points
Other Parts Discussed in Thread: DP83620

We have a customer needing to connect two DP83620 PHYS back to back via the MII interface.  In this case is a delay required in the clock as shown in the attached drawing?

Thanks for your help.

Regards,

John

5023.PHY_Block_diagram.pdf

  • 0
    TI__Mastermind 21326 points

    Hi John,

    I am moving your question to the Ethernet forum so the correct team can address your question.

    Please post all new Ethernet PHYs, Ethernet MACs and Ethernet SerDes questions into the Ethernet forum:

    http://e2e.ti.com/support/interface/ethernet/f/903.aspx

    Thanks,

    John

  • 0 in reply to John Griffith
    TI__Mastermind 31600 points

    In order to connect the DP83620 PHYs back-to-back, they should both be operating synchronously.  The preferred way to do this is to configure both devices for RMII mode. 

    The DP83620 supports RMII Master mode, whereby it can operate in RMII mode when using a 25MHz crystal for its reference clock source.  We have an application note on this functionality at:

    http://www.ti.com/litv/pdf/snla101a

    One possible implementation would be to configure one PHY in RMII mode.  The second PHY would be configured for RMII Master mode and would provide a 50MHz clock to the first PHY as its reference clock source.  This will provide synchronous clocking with a minimum of components.

    Patrick

  • 0 in reply to Patrick OFarrell
    Genius 4430 points

    Hi Patrick,

    Sorry about wrong placement of the question.  Thanks for your help!

    Regards,

    John

  • 0 in reply to WhiteHorse
    TI__Mastermind 31600 points

    John, 

    Closing the loop on this based on some lab work to confirm the best configuration for this application.  The key configuration requirements for each device are:

    1. RMII Master device:
      1. Strap RMII mode by pulling RX_DV high via a 2.2 kOhm resistor.
      2. Strap RMII Master mode by pulling TXD_3 high via a 2.2 kOhm resistor.
      3. Use 25MHz crystal for reference clock source.
    2. RMII Slave device: 
      1. Strap RMII mode by pulling RX_DV high via a 2.2 kOhm resistor.
      2. Use RMII Master device TX_CLK or RX_CLK for reference clock source.

    The RMII data connections (TXD[1:0] to RXD[1:0]) are straightforward.  The RX_DV output of one device should then be connected to the TX_EN input of the other device. 

    Patrick