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Monitoring RS485

Discussion in 'Electronic Design' started by Daniele, Nov 29, 2005.

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  1. Daniele

    Daniele Guest

    Hi all,

    i need an informatio about rs485:
    I need to watch netwrok trafic from my device and another device that
    use rs485 to comunicate. Is possible to connect in parallel mode
    another peripherical (like a pc via rs232) to trace all the message
    that is exchange from two device?

    Thanks in advanced

  2. Deefoo

    Deefoo Guest

    Yes, but if it is two way communication it may be difficult to figure out
    who is sending what.

  3. Guest

    Connecting nodes in parallel - yes, this is what RS485 is designed for.

    If you want to connect a PC via RS-232 then you need to convert RS485
    signal levels to RS232. Since you only want to listen this is simple.
    Connect a MAX481 back-to-back with a MAX232, with the MAX481 configured
    to permanently recieve and the MAX481's recieve data pin connected
    directly to the MAX232 transmit data pin.
  4. John - KD5YI

    John - KD5YI Guest

    Or get RS232/RS485 converters here:

    I'm not affiliated with them in any way.

  5. Ken Taylor

    Ken Taylor Guest

    I did exactly this by just plugging a multiport RS485 card into a PC and
    using the receives of two different ports to monitor the traffic in either
    direction. A quick-and-dirty VB application displayed the results. Still
    does, actually..... :)

  6. john jardine

    john jardine Guest

    Had a 9600 baud setup that broke into gibberish after a few characters were
    sent down the line.
    Quick and cheap solution was to monitor the RS485 wires using the "+" "-"
    inputs of a LM393 comparitor.
    LM393 and its output resistor both powered from spare data pins on the PC's
    LPT1 port.
    Data at the LM393 output pin was sampled at variable rates upto 200kHz from
    a PowerBasic programme.
    Stored data block allowed a storage scope type display of the actual RS485
    voltage transitions. Data decoding and fault finding at my leisure.
    10 minutes to build the device and a hour to programme the software.
    Nowadays we are no longer allowed to do it this way.
  7. Daniele

    Daniele Guest

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