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DP83867IS: Forcing 100BASE-TX Mode

Matthew Force104227
Prodigy 130 points
Part Number: DP83867IS

I have a design that uses 6x DP83867 connected to an FPGA using SGMII.  Two of the devices will only be wired for 100BASE-TX.

1) I don't see a hardware strapping option to do this so I assume it must be done using the Speed Select bits in BMCR?

2) In this case, which MDI pairs are mapped to RX and to TX?

Thanks,

  • +1
    TI__Expert 5425 points

    Hi Matthew,

    1. There are straps that enable SGMII and disable auto-negotiation to enter forced mode. However, you are correct in that there is no strap for forced mode speed. By default in the registers, the speed is set to 1000M, so you will have to write to the Speed Select bits in BMCR.
    2. The DP838867 by default can determine if a straight or crossover cable is used, so RX and TX designations are not needed. If you are forcing 100M, I can assume you will only use two pairs (pair 1 & 2 and pair 3 & 6). In that case, as long as one pair is connected to channel A, and the other pair connected to channel B, you should be good. MDI_Crossover bits in PHYCR register controls the crossover configuration.

    Regards,

    Adrian Kam