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DP83869HM: PHY Detection over SMI Interface ( MDC/MDIO )

Manoj Chate
Prodigy 180 points
Part Number: DP83869HM

Hi Team,

We have DP83869HM over SMI bus along with other 2 device on same bus with all devices supporting clause 22.

While probing this bus with standard 2.5MHz MDC clock , I observed that not all devices are getting detected and only 1 device was getting detected with correct PHY address. But , if I change the SMI bus clock to 1MHz , all devices are detected with correct PHY address.

Why is it so that even if datasheet says that TYPICAL clock required is 2.5MHz , correct address is detected at 1MHz only. Though there is no as such minimum clock , but then PHY should get detected at 2.5MHz as well.

Thank You

Manoj

  • 0
    TI__Mastermind 36540 points

    Hi Manoj,

    Can you confirm the pullup resistor you have on the MDIO line? There should only be a single 1.5k resistor on the line even though you have 2 DP83869HM's connected on the same node. In addition, how is your layout of those lines? Non-optimal layout (long trace lengths, etc) can create board parasitics that come into more of a factor when the signal on the line is a higher frequency.

    Sincerely,

    Gerome