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USB-2-MDIO: Register values read from DP83TC812 are rotated

Part Number: USB-2-MDIO

Hi,

I have connected the MSP430F5 to a DP83TC812 MDIO interface, using the USB-2-MDIO application, and I have seen that the response from reading a register is rotated.

See below: instead of default value 2100, the value is 4201. Can it be changed to report proper value? is this valid also for write? What is the issue

Thanks!

  • Hi Iosif, 

    What do you mean by rotated?

    I see indeed you are reading 4201 which is odd, how do you have the PHY connected?

    Are you able to link-up and send packets? Double check you have MDIO and MDC connected to the correct ports. 

    Default value should be 2100 as you mention.  

    4201 - 0100 0010 0000 0001

    2100 - 0010 0001 0000 0000

    So its almost as if it is shifted except for the 1 on bit 0. 

    Indeed odd. Let me the answer to my questions.

    Best,

    Alon

  • Hi Alon,

    Thank you for your feedback. Indeed seems shifted but also with bits flipped. I have the PBY connected, yes through a level shifter on MDIO made discrete with FET since PHY MDIO is 1.8V and MSP is not working with 1.8V. Level shifter seem to work fine.

    I have noticed a wrong behavior of MSP:

    If you look at MDIO, there is a LOW spike at the frame beginning. On MDIO there is pull up to 1.8V as per standard.

    Here is a capture of MDC/MDIO without the PHY connected:

    So it seems to me that before sending the READ frame, the MSP port somehow is set LOW at the frame beginning and is not open drain, but push pull?

    this spike  seems to mess with the frame decoding.

    LATER EDIT: I changed the VDDIO of the PHY to 3.3V, so now MSP board is connected without level shifter and USB2MDIO works fine.

    Still, the glitch at the beginning of the frame is there, probably when switches from push pull to opendrain?

    Due to this glitch the SALEAE tool does not decode properly the frame:

    but, the USB2MDIO reports good values and write works too....

  • Hi Iosif,

    Glad to hear USB2MDIO is working fine now. That is an interesting setup you have going. 

    I am not familiar with SALEAE tool, what is it?

    We do expect the MDIO signal to go low at the beginning of the operation so that makes sense. 

    Interesting result however.

    Best,

    Alon