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Original question:

DP83848C: BMSR - Link Status Flag never set when connect two device together

DP83848C: Transmit failed occasionally

Luke Zhang11
Prodigy 60 points
Part Number: DP83848C

Hi all,

I'm trying to implement the ethernet module (FEC) using MPC5777c chips with official MPC57xx motherboard for RJ45 hardware interface,and I'm using the DP83848C for PHY layer chips.

Now I'm at a stage that receiving part are always working, but sometimes I couldn't transmit packets. Sometimes the transmitter is working but sometimes it is not, and I checked all the registers on the chip they all behaves the same when the transmission successful or not. I'm thinking maybe it's due to the packet collision or some other reasons which cause the packet couldn't transmit? I'm currently run out of my idea, since all the software part behaves exactly the same whenever it's success or failure. Could anyone give me any clue of how to check that this chip is working correctly and whether it is causing via a data collision or some other reasons? Thanks. 

Here's some screenshot when it successful and failure.

when it working:

when it not working:

Regards.

Luke

  • 0
    TI__Mastermind 18425 points
    Hi Luke,

    Is the schematic posted in the older thread still applicable? If yes, I see that the RBIAS resistor is 4.7kohm. As per the datasheet, it should be 4.87kohm with 1% tolerance. Can you replace the resistor with correct value and try again?

    Are you using MII mode with 25MHz crystal as reference clock input? What is the load capacitance value mentioned in the crystal datasheet? Please also check that the crystal meets the datasheet requirement. Also check if magnetics requirements are met as per the datasheet.

    -Regards
    Aniruddha
  • 0 in reply to Aniruddha Khadye
    Prodigy 60 points

    Hi Aniruddha,

    Thanks for that. By changing the value from 4.7kohms to 4.87kohm does fix the bug! By the way, I just checked that the load capacitance is 20pF of the crystal, and I found the datasheet requires the capacitance is from 25 - 50 pF. Do I need to change this as well or I can leave it?

    Cheers,

    Luke