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RS422 inverted

Discussion in 'Electronic Basics' started by [email protected], Oct 14, 2006.

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  1. Guest

    I am reading RS422 data into a computer. However, the data is only
    correct if I flip the bits (one's complement). Any ideas why?

    I looked on an oscilloscope, and it looks like the ones are high and
    the zeros low.
     
  2. Dana

    Dana Guest

    In reference to what?
     
  3. Chris

    Chris Guest

    OK. Common problem. Common solution -- flip the two wires. Happens
    all the time with twisted pairs. A and B reversed is by far the most
    common setup problem with RS422 and RS485.

    Good luck
    Chris
     
  4. Guest

    Flipping the two wires does not work. That also flips the start bits,
    stop bits, and parity bits, which messes everything up.
     
  5. Rich Webb

    Rich Webb Guest

    That would seem to indicate that the hardware is okay and that you have
    a software problem, either with what you load into the transmit holding
    buffer or with a configuration bit instructing the UART how to handle
    the byte that's loaded into the outgoing buffer. What does the data look
    like upstream of the '422 line driver?
     
  6. john jardine

    john jardine Guest

    You'll have to add a harware inverter somewhere. RS485 is not RS232 and the
    RS485 data can be in any format that appeals to you.
    The UART in Micros such as PICs etc, expect RS232 format input, which means
    the static, line-idle, inactive, no data, level at the UART input pin is
    logic 1, ie +5V. A RS232 'start' bit then drops the pin to 0V.
    The UART making the assumption that the RS232 data has been inverted whilst
    coming off of the comms cable.
    john
     
  7. Chris

    Chris Guest

    OK. Bob. Please describe the hardware you're using on both sides.
    Also, did this work before, or is it a new setup?

    Any additional information would be helpful, the more the better.

    Thanks
    Chris
     
  8. Jamie

    Jamie Guest

    yup, thats normal..
    it makes it easy for you to use a
    level Inverter.
    you can drive the computer with the
    level of voltage needed and invert it
    as you go.
     
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