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RS 485 on advantech PCM-4153 board

Discussion in 'Embedded' started by muktabh, Feb 7, 2008.

  1. muktabh

    muktabh Guest

    I have an advantech PCM-4153 board with 4 com ports. The user guide say
    port 2 can be configured as a RS485 port. I have a few doubts.
    I am using linux on this board. Will I need special drivers to use RS485
    (the board uses sch3112 chip for IO) The user guide says to set a jumpe
    to switch from rs232 to rs485. Will I need to change the serial comm cod
    Is it OK if i do this:
    1) COM 2 is configured as a serial port right now.
    2) I dont change the code, just set the jumper to RS485.
    3) I run the code, connect COM 2 to a RS485 to RS232 convertor, and rea
    in the output in using hyperterminal.

    Will the above work?

    muktabh, Feb 7, 2008
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  2. I don't know that specific board (have dealt with other PCM cards), but
    typically RS-485 needs some line discipline. Strictly speaking, RS-485
    is half-duplex (3-wire: 2 for comms, 1 for ground); you either tx, or
    you rx. Not both. Something (often the RTS output) needs to
    enable/disable the drivers.

    Again strictly speaking, the 5-wire version (full duplex) is RS-422, but
    the distinction is getting a bit blurred - people talk about FDX RS-485
    links these days (which is mostly ok - RS-485 drivers are way more
    robust than RS-422 drivers). If your board has a distinct pair of RS-485
    outputs and another distinct pair of inputs, you'll be fine. Otherwise,
    you'll need to enable the drivers while you tx (and for a short while
    afterwards, long enough for the last character to leave), and disable
    the drivers when you rx or when you're idle.


    Steve at fivetrees, Feb 7, 2008
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