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DP83867E: PHY isolation when in loopback mode

Kathy Hadley
Prodigy 20 points
Part Number: DP83867E

When the DP83867E is configured in Analog Loopback mode, is the data that is transmitted just looped back, or is it also transmitted onto the media (MDI)?  Section 8.4.4.1.1 of the data sheet says that "While in MII Loopback mode the data is looped back, and can also be configured through register to transmit onto the media."  But no similar statement is made for any of the other Near-End Loopback modes.  For the embedded testing that I am doing, I need to just have the data looped back and NOT transmitted onto the media (i.e. suppress data to the MDI).

Also, while in Analog Loopback mode, is the PHY isolated from the media, so that it does not receive any messages from the media?  Again, I need to ensure that the only messages received while in Near-End Loopback mode are those that I am transmitting (i.e. suppress data from the MDI).

As a side note, I suggest that the data sheet be updated to clarify that the register mentioned in section 8.4.4.1.1 is the BIST Control Register (section 8.6.20).  Since MII Loopback mode is selected through the Basic Mode Control Register (8.6.1), it's not obvious which register is used to transmit MII loopback data onto the media (MDI).

Thank you!

  • 0
    TI__Mastermind 18425 points
    Hi Kathy,

    In analog loopback mode, data received from the MAC will be looped back to the MAC without being transmitted on the MDI. The option to transmit MAC loopback data on to the MDI channel is applicable to only MII loopback. When the PHY is in Analog loopback mode, it shouldn't forward the data from MDI to MAC. You can also disable the 1000M link when you are testing in Analog loopback mode.

    Register 0x00 is defined by IEEE so the feature to allows MII loopback data to transmitted on MDI had to be included in other register, 0x16 in this case. Register 0x16 bit [6] states that this feature can be used on MII loopback only.

    -Regards,
    Aniruddha
  • 0 in reply to Aniruddha Khadye
    Prodigy 20 points

    Aniruddha,

      Thank you for the reply.  That answered my main question.

      I understand why the feature to allow MII loopback data needed to be put into a different register.  I do feel that that data sheet would be more clear if you changed "... can also be configured through register to transmit onto the media" to "... can also be configured through the BIST Control Register (8.6.20) to transmit onto the media".

      Best regards,

    Kathy