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DP83848 Link LED

Mehran Msba
Prodigy 130 points

DP83848 works and I can ping my device,but some problem in led indication.

When my board boots up and network cable is unplugged Link_LED is off and in this step its OK.

This LED turns on after plug the cable and its OK too.

But when I unplug the cable,Link_LED is still ON !

I read BMSR register and link status is 1(valid link)! I read this register twice(or many more!) but this register always return valid link.

Is there any issue in my work?

additional info:

RMII connection,LED_Mode is default(Mode1).

  • 0
    TI__Mastermind 31600 points

    I want to make sure that I understand the functionality correctly.  After a link has been established and the cable is removed, the BMSR link status bit continues to indicate a link?

    Is this a new design?  On how many boards has this functionality been seen?

    Patrick

  • 0 in reply to Patrick OFarrell
    Prodigy 130 points

    Thanks.

    "After a link has been established and the cable is removed, the BMSR link status bit continues to indicate a link?"

    Exactly. bit 2 of BMSR is high,link_led is on too.

    "Is this a new design? On how many boards has this functionality been seen?"

    Its a prototype and I have one board.

    Its seems you think about chip damage,don't it?

  • 0 in reply to Mehran Msba
    TI__Mastermind 31600 points

    Chip damage is one possibility.  A configuration issue is another possibility. 

    If the LED were not configured correctly, it could have indicated link when the device no longer saw link.  In that case, the LED would be lit, but the BMSR bit would be low.

    Could you provide a schematic of your design for review?  It would be best to confirm the configuration and then consider possible avenues for debug.

    Patrick

  • 0 in reply to Patrick OFarrell
    Prodigy 130 points

    Schematic is completely same as a this topic.

    You checked it formerly.

    What can I do?

    Thanks.

  • 0 in reply to Mehran Msba
    TI__Mastermind 31600 points

    OK, now I remember.  The schematic looks fine. 

    This may be caused by damage to the chip, but it would be worthwhile to make some quick measurements to confirm the basic connections.  You may have already made some of these measurements, but I would double check the following:

    1. Measure the voltage on the 3.3V supply pins.
    2. Measure the voltage on the PFBOUT and PFBIN pins.
    3. Measure the voltage on the RBIAS pin. 
    4. Measure the resistance of the RBIAS resistor with the board powered down. 

    If those values look correct, I would use a scope to probe the X1 reference clock and the MDC/MDIO.  The expected signaling for these signals is described in the datasheet.

    Patrick

  • 0 in reply to Patrick OFarrell
    TI__Mastermind 31600 points

    Were you able to resolve this issue?  Was the chip damaged?

    Patrick

  • 0 in reply to Patrick OFarrell
    Prodigy 130 points

    Thanks for your support.

    I make another board and its work fine.I can read link status without a problem.(with same temperature soldering)

    I changed RJ45 part number and use a part that have POE.

    May be this connector had issue and new part is OK.when I think,I remember this connector(old part number) had LED issue on another board but nobody attend this.

    Can its true?

    I think DP83848 had no damage,I want to change it in future.I will reply the status in this thread.

  • 0 in reply to Mehran Msba
    TI__Mastermind 31600 points

    It is not clear to me how changing the connector corrects the functionality, but I am glad to hear you have successfully resolved the issue. 

    Since you have resolved this issue, would it be acceptable to close this thread?  Any new developments could then be tracked in a new thread.

    Patrick

  • 0 in reply to Patrick OFarrell
    Prodigy 130 points

    I can't change the chip yet and I have no problem in my new design.

    We can close the thread.

    Thanks.