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DP83848C Transmit Signal

Steve Karg
Prodigy 60 points
Other Parts Discussed in Thread: DP83848C

Some of my prototype boards using an DP83848C have this TD signal shape at the CAT5 connection and do not transmit correctly. The signal is similar before the magnetics.  Any ideas where I should look for the problem? The BIST with internal loopback fails.  The receive path is fine, and the Tx/Rx signals were impedance matched in Altium.

  • 0
    TI__Mastermind 18425 points

    Hi Steve,

    We can start by looking at the register values for the PHY. But a few questions before that;

    Out of the boards you tested, did any boards not have this problem? If yes, do they link with known good link partners?

    Does the PHY on the problem board link with a known good link partner?

    Does the problem go away if the TD and RD pins are swaped by forcing MDI/MDIX?

    Is it possible to get register vlaues from 0x00 to 0x1D when the problem board is connected to good link partner in default mode?

    -Regards,

    Aniruddha

  • 0 in reply to Aniruddha Khadye
    Prodigy 60 points
    All of the boards that were tested worked initially, but then after a period of time or some other trigger, stopped connecting via Ethernet. I don't have access to all the other failed or good boards, only the single one with the problem exhibited. I developed the firmware on a different prototype board, which is still working fine at 10-BaseT. I have the problem board connected to a 10-BaseT hub. The board Ethernet link light is active, and it is lit on the hub, and the board receives Ethernet frames successfully.

    I'll try forcing MDI/MDIX. I'll also read register values from 0x00 to 0x1D.
  • 0 in reply to Steve Karg
    Prodigy 60 points

    Register Value
    -------- ------
    0x0000 0x1000
    0x0001 0x786d
    0x0002 0x2000
    0x0003 0x5c90
    0x0004 0x01e1
    0x0005 0x0021
    0x0006 0x0004
    0x0007 0x2001
    0x0008 0x0000
    0x0009 0x0000
    0x000a 0x0000
    0x000b 0x0000
    0x000c 0x0000
    0x000d 0x0000
    0x000e 0x0000
    0x000f 0x0000
    0x0010 0x0013
    0x0011 0x0000
    0x0012 0x3400
    0x0013 0x0000
    0x0014 0x0000
    0x0015 0x0000
    0x0016 0x0100
    0x0017 0x0021
    0x0018 0x0000
    0x0019 0x8021
    0x001a 0x0904
    0x001b 0x0000
    0x001c 0x0000
    0x001d 0x6011

  • 0 in reply to Steve Karg
    Prodigy 60 points
    After Forcing MDIX, the link is not established:

    DP83848 Ethernet PHY
    Register Value
    -------- ------
    0x0000 0x1000
    0x0001 0x7849
    0x0002 0x2000
    0x0003 0x5c90
    0x0004 0x01e1
    0x0005 0x0000
    0x0006 0x0004
    0x0007 0x2001
    0x0008 0x0000
    0x0009 0x0000
    0x000a 0x0000
    0x000b 0x0000
    0x000c 0x0000
    0x000d 0x0000
    0x000e 0x0000
    0x000f 0x0000
    0x0010 0x4000
    0x0011 0x0000
    0x0012 0x3000
    0x0013 0x0000
    0x0014 0x0000
    0x0015 0x0000
    0x0016 0x0100
    0x0017 0x0021
    0x0018 0x0000
    0x0019 0xc021
    0x001a 0x0904
    0x001b 0x0000
    0x001c 0x0000
    0x001d 0x6011
  • 0 in reply to Steve Karg
    TI__Mastermind 23675 points

    Hi Steve,

    Can you send me the schematic? 

    You have a 50MHz oscillator driving into XI pin?

    Kind regards,

    Ross

  • 0 in reply to Ross Pimentel
    Prodigy 60 points

    Yes, I'm driving X1 with STM32 50MHz oscillator pin per STM32F107xx datasheet:

  • 0 in reply to Ross Pimentel
    Prodigy 60 points

    Here is the relevant portion of the schematic: