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DP83849IF: loss of link connection

Guenter Fettig
Intellectual 1540 points
Part Number: DP83849IF

Twisted pair and FX line connected to PHY in parallel.

If link get lost at FX line, this will not be recognized at twisted pair line.

Is it possible to indicate FX loss at twisted pair line also ?

Pin strapping preferred, compared to software solution.

If not possible with DP83849IF, how to realize ?

  • 0
    TI__Mastermind 23675 points
    Hi Guenter,

    FX line and TX lines are completely different and are able to achieve links with connected partners independently.
    It is not possible to force a link down on one side if the other side has a like drop.
    The only way to achieve this is if you have a simple micro that is monitoring and makes a decision through MDIO/MDC to kill the other link.
    You can configure an interrupt for link loss and then use register access to force a link drop on the other line.
  • 0 in reply to Ross Pimentel
    TI__Intellectual 1540 points

    " You can configure an interrupt for link loss and then use register access to force a link drop on the other line. "

    Can you please describe, what registers need to be accessed and how ?

    Is there a chance for fast link restart after interrupt ?

  • 0 in reply to Guenter Fettig
    TI__Mastermind 23675 points
    To enable link loss interrupt on the INT pin, please do the following:
    1. set bit[1] in register 0x11
    2. set bit[0] in register 0x11
    3. set bit[13] in register 0x12

    I am not sure what you mean by fast link restart.
    The PHY will try and re-establish link immediately after it loses link.
  • 0 in reply to Ross Pimentel
    Hallo Mr. Pimentel,

    can you please describe with which register I can set die "Link Drop" for the Ethernet PHY?
    -> (Your Message from Jul 9, 2018 8:54 PM ) ... and then use register access to force a link drop on the other line.

    Thank you.

    Best regards,

    Andreas Wanjek
  • 0 in reply to Andreas Wanjek
    TI__Mastermind 23675 points
    Hi Andreas,

    There are a few methods.
    1. if using auto-negotiation, you can set bit[9] in register 0x0
    2. if using forced mode or auto-negotiation, you can set bit[15] in register 0x0
  • 0 in reply to Ross Pimentel
    Hi Ross,

    Thank you for the answer.
    This Register are just to restart/reset the process to build a link.
    I need a register were i can purposefully drop down the link by configuration.
    At the moment i use the 10th bit(TQ-EN) in the register PCSR (16h). When I set this bit, I've got no link on the Ethernet-Interface. And when I set it to '0' the link will rebuild. But it takes up to 1.5 seconds. Is there a register/bit where I can use to be faster?

    Best regards,

    Andreas
  • 0 in reply to Andreas Wanjek
    TI__Mastermind 23675 points
    Hi Andreas,

    Are you using forced 100Mbps operation or auto-negotiation on the copper side?
    If you force to 100Mbps instead of auto-negotiation you should be able to cut down on your link-up time.
    Since 100Mbps is only supported for FX operation, this could be an option on the copper side so long that your link partners support parallel detection.