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DP83848I-MAU-EK: Far field loopback test

Part Number: DP83848I-MAU-EK

Hello folks,

I am looking to do test of the 83848 with the DP83848I-MAU-EK/NOPB prototyping board.  What I need to do is send data from a bit error rate tester (BERT) through the RJ45, into the phy and then back to the BERT.  I can't seem to find any far end loop test option similar to the 83867.   I am using the usb2mdio tool with the MSP430.   I can read and write to the PHY on this prototyping board.  I thought to use these settings.

//Reset on BMCR
0000 8000
//Set BMCR to loopback B14 and auto-neg B12
0000 1000


But, realized after I started it that it wasn't the loopback mode I wanted and was actually looping back the wrong direction.   Then I thought I could just jumper the Tx3:0 pins to the RX3:0 pins and maybe the rxclk to the txclk and none of this seems to be working.   Any suggestions would be greatly appreciated.  What I need to do is test the phy under extremes of environments.   Please and thank you.


  • Hi Craig,

    DP83848 does not support Reverse Loopback like the DP83867. Also, in MII mode it is not possible to create a loopback by connecting the TXD[3:0] pins to RXD[3:0] pins. Both transmit and receive clocks are output, so the data cannot be clocked properly in this configuration. In order to perform loopback on the MAC side, you would need to use RMII mode. Then you can connect the RMII TX pins to RMII RX pins and perform loopback.

    If you wish to evaluate MII mode, then you will have to send in data through the MII pins with your BERT device acting as a Ethernet MAC. Then on the cable side you will need to use a loopback cable. For a loopback cable, connect pin 1 of RJ-45 to pin 3 and pin 2 to pin 6.