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Ethernet interconnection between two embedded PC's inside one box

Discussion in 'Electronic Design' started by Bert, Feb 29, 2008.

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  1. Bert

    Bert Guest


    I have a question about interconnecting two embedded PC's by Ethernet.
    Our situation:

    - PC A has the LXT9785 Ethernet PHY of Intel, internal termination,
    with 1:1 transformer and 1nF/2kV capacitor at the TX and RX center
    taps at the secundairy side.

    - PC B has the 82562ET Ethernet PHY of Intel, termination near PHY,
    without 1:1 transformer. The specification of this ethernet PHY
    describes the use of a 1:1 transformer with a 75ohm in series with a
    1.5nF/2kV capacitor at each center tap at the secondairy side.

    Question: has someone experience with interconnecting Ethernet ports
    of two embedded PC's without using a transformer at one of the PC's,
    in our case PC B? What are the consequences, limitations or general
    issues? The distance between these two PC platforms is apporx. 15

    All suggestions are welcome.

    Kind regards,
  2. Guest

    If both embedded PCs have the same potential (GND to GND = 0 Volt) and the
    distance is "short" then:
    *) You can drop both PHY and wire MAC to MAC.

    If potentials differ or the distance is too long. Then you can:
    *) Remove one magnetics transformer.

    This ofcourse requires that all persons handling the equipment are aware of
    this issues when handling units or expanding them. Ie a motor drive on one
    of them may make the first solution unsuitable.
    The second solution requires that the network wire isn't reconnected to any
    other unit that is also unisolated.
  3. donald

    donald Guest


    Can these two PCs connect to each other by a hub or switch ??

    If so then a cross over cable will work just fine.

  4. JosephKK

    JosephKK Guest

    ^^^^^ Sounds a bit cheesy to me.
  5. whit3rd

    whit3rd Guest

    Much of Ethernet's cost is in the interface to that unshielded twisted
    long wire.. You can omit transformers and such, but... why Ethernet
    at all? Multiprocessor communication is usually through shared
    (two-port) RAM, isn't it? Or even a pair of FIFO RAMs?

    I'd either use a standard processor board with the full Ethernet
    hardware, and treat the ports as useful for breaking out signals
    for maintenance, OR go with a full-custom shared memory.
  6. Bert

    Bert Guest

    I understand that there arte better solutions for communication
    between two PC's, but in this system we have not the opportunity to
    chose another interface. Ethernet is the only available interface.
    Thank you all for your suggestions !!!
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