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DP83869HM: SMI register access not working

Georg Waibel
Prodigy 10 points
Part Number: DP83869HM

Hello,

i'm failing to read the SMI registers of the DP83869HM device on our design. For most registers I get the value 0x8AD1 (including PHYIDR1/2), some return 0. I have no idea why i get this register value. 

MDC/MDIO signaling looks ok. Accessing other PHYs on the same lines works. I'm using the same PHY address that has been selected by strapping (0x0F).

In the datasheet I found this hint at the description of pin INT_N/PWDN_N: "When register access is disabled through pin option, the interrupt will be asserted for 500 ms before self-clearing". However, i found no other hints on how the register access could be disabled. Might this be the problem in our design?

Thanks
Georg

  • 0
    TI__Mastermind 25745 points

    Hi Georg,

    For a further debug, I may need to aske you couple question:

    • Are you able to share the schematic for the strapping on your PHY ID?
    • Could you also send a snapshot on MDC and MDIO signaling?

    --

    Regards,

    Hillman Lin

  • 0 in reply to Hillman Lin
    Prodigy 10 points

    Hi Hillman,

    here's the schecmatic of the strapping pins:

    ...and the MDIO signaling (RD, PHYAD=0xF, REG=0x2):

    The first part of the communication in detail:

    Regards
    Georg

  • 0 in reply to Georg Waibel
    TI__Mastermind 25745 points

    Hi Georg,

    From the strap setting you shared with me, Did you populate R241 and R242 in your actual board? For example, if you are trying to populate PHYID 01, your strap setting should be R246 = 10kohms, R241 = 2.49 ohms, R247 = DNP, and R242 = DNP.

    --

    Regards,

    Hillman Lin

  • 0 in reply to Hillman Lin
    Prodigy 10 points

    Hi Hillman,

    I could solve the problem. The voltage level of the  RESET_N signal was in an unspecified range which caused the PHY to freeze and always return the same register value for all MDIO accesses.

    Thanks for your support.

    Regard
    Georg

  • 0 in reply to Georg Waibel
    TI__Mastermind 25745 points

    Hi Gerog,

    Glad to here that. Please let me know if you have further question. I will close this thread for now.

    --

    Regards,

    Hillman Lin