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Serial communications over 2 wires?

Discussion in 'Electronic Design' started by news.valornet.com, Jun 26, 2006.

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  1. Hi,

    I have a diagnostic tool that records information. It has some sort of a
    proprietary interface port on it, just 2 conductors. I can tell one of them
    is ground. The remote that normally hooks to this interface port has some
    sort of two way communicatoin with the diagnostic tool. It can send
    commands to the tool, but mostly the remote outputs to a serial device at a
    very slow speed. I would prefer not to have to purchase the remote device
    and make my own so that can get information from the diagnostic tool. I
    wonder if the tool itself outputs in serial and I just need to hook up to
    it.

    Can the RX and TX pins in a serial interface be combined to a single pin
    somehow? I really expected to find 3 conductors.

    Is there any way of using a DMM to find out if the 2 conductors (one ground)
    is a serial interface? The resistance between them is about 4.7k. I don't
    see any voltage on them.

    How could/would communication like this occur over 2 conductors that
    involves slow serial (1200 baud)?

    TIA!
     
  2. Luhan

    Luhan Guest


    Easy, open-collector drivers (or Tri-States) at both ends. This is
    assuming one conductor is a ground.

    Otherwise, 2 wires makes a current loop with both sending and receiving
    at both ends.

    Luhan
     
  3. Visit the Maxim/Dallas web site, and have a look at their '1 wire bus'.
    Really a misnomer, since there has to be a second 0v connection to
    complete the circuit, but one a single 'signalling' wire, which can carry
    power as well. Quite a lot of things like weather station senders etc.,
    use this interface.

    Best Wishes
     
  4. Yes. As someone else stated, using open collector drivers is one
    technique.
    Better to use an oscilloscope. A DMM might be able to detect a longer
    message. Put it in AC mode and try. But if it has a slow response time,
    you're likely to miss the signal.
    The communications protocol includes commands for reversing the data
    direction. Or certain commands are structured so that the master prompts
    the slave to reply and then listens for a certain amount of time.
    --
    Paul Hovnanian mailto:p
    ------------------------------------------------------------------
    100 buckets of bits on the bus
    100 buckets of bits
    You take one down,
    and short it to ground
    FF buckets of bits on the bus
     
  5. Jamie

    Jamie Guest

    i think your talking about open collector Txing ? that is where you
    can tie the TX over to the RX via an open collector from the TX side.
    its a single wire (with common) form of bi-directional serial.
     
  6. delo

    delo Guest

    The videocamera LANC interface work with ground and only one
    signal with open collector.
    To find the common - gnd pin (if you ave access to internal circuit
    or the common of power supply, or the negative terminal of a battery),
    try the continuity with one of the two pin You have, You MUST use
    a continuity tester with a negligible ddp (continuity tester) not a
    normal multimeter wich put too much voltage on the tested circuit.
    Such testing device is quite useful to deenginnerig a board without
    damaging it, and can be built with a simple lm393 and 6 resitors.
    In MHO the scope is a must You must measure the level of "one".
    In the case of oc if the pull up is on the device when the line is idle
    You can measure about Vsupply, different case if You are in presence
    of 1wire interface, btw if you have access to the inside You can figure
    out wath kind of interface chip is placed in.

    bye
    delo
     
  7. Guest

    Try to use DC power line communication. You can transfer both data and
    power on the same wires. There are transceivers for speeds of 10Kbps to
    500Kbps. Try www.yamar.com

    Taly.
     
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