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DP83869HM: Media converter mode not working

John Swenson76
Intellectual 320 points
Part Number: DP83869HM
Other Parts Discussed in Thread: DP83869

I just got a new board in which uses a DP83869HM as a simple media converter. SFP cage connected to fiber pins, copper Ethernet to RJ45 with integrated magnetics.

Configuration is just with straps, no SMI interface is connected.

The copper Ethernet connects up perfectly to all link partners I've tried But a logical connection through the SFP module to a different FMC does not connect. I didn't put some test points on this board to hook up the high speed differential probe so I'm not sure if the differential pairs to the SFP module are really working. I've done an SFP connection with other chips before so I'm pretty sure I did it correctly.

The other boards I've done with SFP modules did not use the LOS signal from the SFP module, the DP83869 DOES use this signal so I'm wondering if I did it right. I have the LOS connected to a 4.7K pull up resistor to 3.3V, it is connected to the SD pin (#24) on the DP83869. This done according to the diagram in the data sheet. But the data sheet never specifies the polarity or functionality of the SD pin. The LOS pin is a low value when the signal is good. The SD pin is not SDN, so I'm wondering if it is detecting good signal with a high value on the pin? I can't tell since the data sheet never says what the SD pin does.

I will attempt to solder in some test pins to look at the differential pairs going to the SFP module and see what they are doing.

Thanks,

John S.

  • 0
    TI__Mastermind 23675 points
    Hi John,

    Please have a look at section 9.4.8.4 within the DP83869HM datasheet.
    Register 0x1DF is required to operate in media converter mode (MDIO/MDC access).
  • 0 in reply to Ross Pimentel
    Intellectual 320 points
    I finally have this board working.
    I used the EVM to get things working, then worked through the differences between the EVM and my board. There were two primary issues:

    1): I didn't have the LOS pin from the SFP module connected to pin 24. This isn't mentioned in any text, it IS shown in the SFP module connection diagram. I have used other chips from other companies that did not use the LOS signal at all, so I was in the mindset that I didn't need it. Some text ether in the description of the SD pin or when talking about the fiber modes would have helped a lot with this.

    2): I had one of the LED straps set incorrectly. That was just mis-interpreting the description of the strap. Of course since it is an LED strap I had to do a lot of board hacking so the LED worked properly with the opposite strap value.

    This process of comparing EVM schematic to my board was severely hindered because the published EVM schematic didn't match the actual EVM board. That needs to get fixed.

    Having the EVM helped immensely, I had the EVM up and running in less than a day, so I KNEW it could be done, that actually made a big impact on debugging.

    John S.
  • 0 in reply to John Swenson76
    TI__Mastermind 23675 points
    Hi John,

    Thank you for the feedback. I will pass this along to my colleagues so that we can fix those discrepancies.
  • 0
    Intellectual 630 points

    Hi John,

    Your post was timely for me. I will be using the DP83869HM as well in a fiber media converter application. Can you confirm that you did NOT need to connect the SMI pins. I would prefer to use pin strapping only.

    Thanks,

    Mitch

  • 0 in reply to Mitchell Kary
    Intellectual 320 points

    Yes, I did get it to work with just strapping pins. No MDIO interface needed.

    John S.