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Original question:

dp83848 could not establish ethernet connection

DP83848C: dp83848 could not establish ethernet connection

Qiong LIU
Prodigy 40 points
Part Number: DP83848C

Hello, everyone. 

I've some issues on the ethernet phy device DP83848.

At speed 100mb/s (autonegociation), the green LED (LINK) blinks and never stays ON. 

I think it means that the link is not established

At speed 10mb/s, everything work. the LINK LED stays ON and the pcb can get its ip address by DHCP. 

I don't think that it's problem from the software. 

Beause,even if there is nothing in the microcontroller, once we plug the RJ45 cable, the green LED should be light and stays ON. 

I've downloader an CAN demo example into my demo board (MCB1700) and then I plug the RJ45 cable to the demoboard. 

The link LED turns on immédiately even if the ethernet is not initialized. 

But when I did the same thing with the PCB, the LINK LED blinked and never stays ON. 

This problème is only detected on serveral PCB. 

Do you have some idea about this problee? 

  • 0
    TI__Mastermind 18425 points
    Hi,

    What is the link partner when using 100Mbps connection?
    Can you read register 0x01 multiple times when the LINK LED is blinking and provide the values? Also provide the register read value for 0x19 when this problem is occurring.

    -Regards,
    Aniruddha
  • 0 in reply to Aniruddha Khadye
    Prodigy 40 points

    Hi

    Thank you very much for your reply.

    Here is the value of register. 

    BMSR(0x01)  = 0x7849

    REG_PHYCR(0x19) = 0x8021

  • 0
    Prodigy 40 points
    Hello, everyone

    I didn't find anyway to make the ethernet function work again.
    I think that the only way to repaire this is to replace the DP83848.

    I checked the voltage on the pins RX+, RX-, TX+, TX- (16,17,13,14) with an oscilloscope.
    The present voltage is around 1,5V or less ( instead of 3.3V in normal case).

    The interface between mcu and the DP83848 is RMII, it seems to be OK. I can read/write the registers in the DP83848.

    Do you have any ideal why the PHY device is damaged so frequently?
    I compare the schema between our PCB and the Keil MCB1700 (the ethernet parts), that's exactely the same.
    The only difference is : the demoboard KEIL MCB1700 is powered by and USB Cable.
    And my PCB is powered by POE+

    Qiong
  • 0 in reply to Qiong LIU
    TI__Mastermind 18425 points
    HI Qiong,

    Powering through USB and POE are different application. When Powering through POE, proper precautions need to be taken in order to avoid damage to the PHY. Can you review this thread and ensure that DP83848 is properly protected from POE transients : e2e.ti.com/.../471071

    -Regards,
    Aniruddha