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DP83848I: Layout with DP83848I

Prodigy 70 points

Replies: 9

Views: 1760

Part Number: DP83848I


I am working on project with ethernet. A have working software with developer board and now I want own hardware. I made schematic and board. For ethernet phy I used DP83848I. I read a datasheet and other documentation and now, I have some layout. Can I post you my schematic and could anybody help me with check? It is really interesting for me, because it is my first layout with this chip. 

It is fo this project: 


Thank you very much!


  • Hi Vilem,

    My feedback is that you should consider decoupling for your supply rails. I'd suggest using the DP83848I-MAU EVM as a reference design and only removing items from that schematic you are sure you do not need.

    You also have connections indicating you are using RMII mode. In RMII mode, a 50MHz reference clock should be provided to the X1 pin and a strap on RX_DV should be used to enable RMII mode.

    Best Regards,

    Rob Rodrigues

    CTS (Clock & Timing Solutions) Systems Engineer

  • In reply to Rob Rodrigues:

    Hi Rob,

    Thank you for referrence design. I changed my design and I attach new version. I read datasheet and I do not understand settings of AN pins. If I want automatic auto-negotiation,  is it needed connect something there?

    And please, could you check oscillator on my design? Is it OK, now? 

    Thank you very much!

    Best Regards,



  • In reply to Rob Rodrigues:

    And for RMII mode, it must be connected pin 39 to Vcc through resistor 2k2?
  • In reply to zavovi:

    Hello Vilem,

    The auto-negotiation strap pin (pin 26, 27, 28) have weak internal pull-up resistors, so by default auto-negotiation will be active. It is not required to have a pull-up resistor in that case. However, in some applications the strap pins are connected to other devices which also have internal resistors. This might cause the ethernet PHY to be strapped in an incorrect mode. In such cases we ask that appropriate strapping resistors be connected to the strap pins.

    The oscillator design look ok, please ensure that the oscillator meets the design requirement mentioned in the datasheet.

    You are right pin 39 should be connected to Vcc via 2.2kohm resistor for RMII mode.

  • In reply to Aniruddha Khadye:


    Thank you for support. I have done board with DP83848I. Communication with microcontroller seems be working, but it can not detect a cable. No lights on LEDs and no communication with router. Could you help me please? Can I try this PHY with ethernet cable without transformer? How can I connect it?

    Thank you

  • In reply to zavovi:

    Hi Vilem,

    Can you send me a register read out for the DP83848I?
    I would like see see register read for register 0x0 - 0x1Fh.

    For a transformerless (without magnetic) operation you can look at this app note:

    Kind regards,

    Best regards,

    Ross Pimentel

    Ethernet - Applications Engineer

  • In reply to Ross Pimentel:

    Hi Ross,
    I connected cable without magnetic transformer and now I can send data from microcontroller via ethernet, but I can not receive.

    Here is register data (cable not plugged):
    CR (0x0000) = 0x3100
    SR (0x0001) = 0x7849
    IDR1 (0x0002) = 0x2000
    IDR2 (0x0003) = 0x5C90
    ANAR (0x0004) = 0x01E1
    ANLPAR (0x0005) = 0x0000
    ANER (0x0006) = 0x0004
    ANNPTR (0x0007) = 0x2001
    ICR (0x0010) = 0x4000
    PSR (0x0011) = 0x0000
    PCR (0x0012) = 0x0000

    Register data (cable plugged into router):
    CR = 0x3100
    SR = 0x786D
    IDR1 = 0x2000
    IDR2 = 0x5C90
    ANAR = 0x01E1
    ANLPAR = 0xCDE1
    ANER = 0x000F
    ANNPTR = 0x2801
    ICR = 0x0015
    PSR = 0x0000
    PCR = 0x2c00

    When I sent the UDP data I am waiting for response, but I did not get interrupt of receive data.

    Thank you,
    Best regards,
  • In reply to zavovi:

    Now, I am debugging ethernet connection and I am receiving some data but I am still getting CRC error of received data.
  • In reply to zavovi:

    This issue is solved, now. It was my fault, I xchange two resistors. Now, it it working! Than you, for your support!

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