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DP83867E: Start of Frame vs 1PPS

Michael Morgan
Prodigy 10 points
Part Number: DP83867E
Other Parts Discussed in Thread: DP83640

Tool/software:

Hello all,

I have a PCB with a DP83867E Ethernet PHY on board.  I need to be able to source and sink PTP (IEEE 1588) and I currently have a DP83867E as part of the design.  This question is about sinking PTP and generating the 1PPS required for time synchronization.  I am wondering, since I cannot seem to find any PHY's that have a 1PPS port, is the SoF (Start of Frame) detect essentially the same thing?  If so, my understanding is that the SoF event is generated before the actual time is read in.  This seems backwards.  If I am mistaken, can anyone provide any advice on how to handle this need.  

Thanks

  • 0
    TI__Mastermind 30090 points

    Hi Michael,

    By '1PPS' you're referring to 1 pulse per second correct? This would not be the same as the SFD signal from DP83867.

    The SFD signal will assert every time an ethernet frame is transmitted from the PHY. It will stay asserted throughout the transmission of the frame:

    For example if you're at 1Gbps speed transmitting 500 byte packets, you should see an SFD pulse roughly every (500*8)/1000 seconds (4 seconds). The actual timing of the SFD pulse will depend on the size of frames being sent through.

    DP83867 does not have a PPS signal port. If you need a PPS signal consider DP83640, which supports 10M and 100M speeds.

    Best,

    Shane

  • 0 in reply to Shane Hauser
    Prodigy 10 points

    Hello Shane,

    Thank you for the response.  Unfortunately, I need a gigabit PHY that interfaces using RGMII and also can output 1PPS.  In doing some research, it seems that the 1PPS may be more of a MAC thing rather than a PHY thing.  I am still trying to figure out all that is needed.  

  • 0 in reply to Michael Morgan
    TI__Mastermind 30090 points

    Hi Michael,

    Understood, unfortunately we don't have a 1G standard ethernet PHY with a PPS signal. Would a single pair ethernet PHY work in your application?

    I can check whether the single pair ethernet PHY team has a 1G PHY with a PPS signal if it would help.

    Best,

    Shane