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DP83848YB in RMII and MII modes with same circuitry

umamaheswara rao jonna
Prodigy 70 points

Hi

My requirement is to test the PHY DP83848 in RMII mode and MII mode with the same circuitry. I have used 25Mhz clock oscillator for MII modeand 50Mhz Osc for RMII mode , which are selected using MUX with a control pin. My question is , whether the RXD{0..3} and TXD{0..3} can connected in both the modes? usually in RMII mode only RXD0,1 are used and RXD2,3 should be open similary TXD0,1 are used and TXD2,3 are GNDed. Can we use a mux logic to connected to the PHY in MII mode and Open/GND in RMII mode ? ( RXD,TXD - 2,3 signals).

regards

Jonna

 

  • 0
    TI__Mastermind 31600 points

    Jonna,

    There are several pins that are used in MII mode, but not used in RMII mode - TXD[3:2], RXD[3:2], COL, TX_CLK, RX_CLK, possibly RX_DV.  It would be best to handle all these signals consistently. 

    What is being used for the MAC?  An FPGA or controller or processor?  Will the physical connections for the RMII signals to the MAC (TXD[1:0], RXD[1:0],TX_EN, RX_ER, CRS_DV, possibly RX_DV) remain unchanged? 

    Patrick

  • 0 in reply to Patrick OFarrell
    Prodigy 70 points

    Patrick

    Controller is used for MAC. Yes, the physical connections of the signals (TXD[1:0], RXD[1:0],TX_EN, RX_ER, CRS_DV, possibly RX_DV) in RMII mode is unchanged.

    Is it not mandatory for the TXD[3:2] signals to be GNDed and RXD[3:2] signals to be open in RMII mode?

    I am worried for adding mux for TXD[3:2], RXD[3:2] signals , which introduces delay only for these in MII mode , which may cause timing issues.

    Thank you for the input

    Jonna

  • 0 in reply to umamaheswara rao jonna
    TI__Mastermind 31600 points

    Jonna,

    It is not mandatory for the TXD[3:2] signals to be GNDed and RXD[3:2] signals to be open in RMII mode.  However, you should make sure that they are not driven or pulled to an incorrect state by the MAC in this mode.  In other words, you want to make sure that the strap pins are in the desired state so that the configuration is not changed.

    Patrick