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DP83867IS: Which 2 pairs are used among MDI interface when DP83867 is configured to 100M mode.

Wayne Wang20
Expert 4380 points
Part Number: DP83867IS

Hi team,

My customer is evaluating DP83867IS but they want to configure it to 100Mbps mode. I noticed that in the page 92 in our datasheet, the default connection is all the 4 pairs MDI lines are connected to RJ45. My question is if we configure it to 100Mbps mode instead of 1000Mbps mode, which 2 pairs are used and which 2 pairs are not used? The used or unused 2 pairs are fixed or can be software configured? Can we leave the unused pairs open? Thanks.

Best regards,

Wayne 

  • 0
    TI__Mastermind 18425 points
    Hi Wayne,

    By default, pin 1-2 and pin 4-5 of the IC are used for 10/100Mbps communication. When mirror mode is activated then IC pins 7-8 and 10-11 are used. It is ok to use only two pairs when 10/100Mbps operation is needed while leaving the other two pairs open. However, care must be take that the PHY is not advertising 1000Mbps speed.

    -Regards,
    Aniruddha
  • 0 in reply to Aniruddha Khadye
    TI__Expert 4380 points

    Hi Aniruddha,

    Thanks for your reply. Customer has some more question about the DP83867.

    1. The MAC is integrated in a 4G module. The ethernet interface of the MAC has 4 data wires SGMII_TX_N, SGMII_TX_P, SGMII_RX_N, SGMII_RX_P but doesn't have the interface to DP83867's SGMII_COP and SGMII_CON. Can we leave SGMII_COP and SGMII_CON open？

    2. If customer doesn't need JTAG interface, can we leave the JTAG pins opne?

    3. Customer wants to configure DP83867 into SGMII mode. I check the datasheet it seems we only need to set LED_0 to MODE2 with strap resistors. Could you please help confirm this? Thanks

    Best regards,

    Wayne

  • 0 in reply to Wayne Wang20
    TI__Mastermind 18425 points
    Hello Wayne,

    1. SGMII can operate in 6 wire and 4 wire interface. It looks like the MAC has 4 wire interface so its ok to leave SGMII_COP and SGMII_CON unconnected.

    2. When unused, its ok to leave JTAG pins open. You can also pull JTAG TDI, TMS, and TDO high using a pull-up resistor (4.7kohm) so that the pins are tied to a deterministic voltage.

    3. Yes, strapping the PHY to SGMII mode via LED_0 should be enough.

    Since this thread is marked as 'Resolved' I would recommend opening a new thread if the customer has follow up questions. This allows us to better track open questions.

    -Regards
    Aniruddha