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RE: Debug DP83848

Sky Lee Dong Lin
Prodigy 10 points

Hi Patrick,

I face some problem on DP83848 that stuck me for a week. My Atmel SAM3X8E MCU can communicate with the DP83848, I can read the PHY ID and it is correct. But when I restart the auto-negotiation, the auto-negotiation complete flag never set.

For additional, when I plug in the Ethernet cable, the LINK and ACT leds are not light up, only the speed led light up.

  • 0
    TI__Mastermind 31600 points

    As a starting point, I would like to suggest that you evaluate the board without connecting to a link partner. 

    The first step in this process will be reading out the contents of the Phy registers.  You mention that you can read the PHY ID.  Could you provide the full register contents?

    The second step in the process will be to evaluate the signaling on the board without a partner.  There will be two parts to this evaluation:

    1. Evaluate the signaling without a link.  For looking at output signaling, I generally use a short (1-2") pig-tail cable with 100 Ohm terminations.   I have attached a picture for reference.  With this cable plugged into the RJ-45 connector, the transmitter will be properly terminated and the voltage levels should be correct.  In this configuration, you can measure the transmit signaling.  I have also attached a picture showing the expected link pulse that should be measured. 
    2. Evaluate the signaling with the device linked to itself.  To allow the link to connect to itself, you will need to create an external loopback plug.  External loopback (also called "line loopback") can be used to loop the high speed lines of the link back to themselves.  The easiest way to achieve this is by making a custom cable and plugging it into the RJ45 connector.
        1. Cut a cable with about 1 foot of cable and the RJ45 connector
        2. Strip off about 3~4 inches of the outside plastic shield to expose the 4 pairs of twisted pair cable
        3. Bend back pairs 4/5 and 7/8 (these will not be used)
        4. Solder pair 1/2 to pair 3/6
              1. Solder wire 1 to wire 3
              2. Solder wire 2 to wire 6
        5. Now you have a loopback cable.
      Plug the cable into any operating 10/100 Ethernet port and link will be established (assuming Auto-Neg is enabled).  You can also force 100BASE-T or 10BASE-T full duplex to test those modes explicitly.  In this configuration, you can measure the transmit signaling.

    Once we have confirmed the device configuration by reviewing the registers and we have confirmed the baseline transmit signaling, we should have a good understanding of the functionality of the device.  If the device is functioning correctly, we can then move to the partner testing to determine what is happening with the partner.

    Patrick

    Pig-tail cable with 100 Ohm terminations:

    Link pulse waveform: