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RS-422 and 485

Discussion in 'Electronic Design' started by Jamie, Sep 4, 2004.

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  1. Jamie

    Jamie Guest

    at work we have an old system that uses a PC and a DOS mode
    program written in TP7.0
    there is a PCI RS-485 card plugged in with what i call some
    smart bios link on it because software simply uses an ESC
    character to the output to make the selection of which device
    out of 32 is going to listen to the stream of data.
    any ways, we need to change the system a bit and also
    the cards.
    can some one give me a quick run down on how the majority
    of the internal cards expect the software to handle the
    sequence of detecting which device input data is coming from and
    which device output data is going to ?
    we can no longer find the old card that we have been using and
    can not find any info at most of the sites other than some supporting
    a protocol calls ADDC or something like that?
  2. Rich Grise

    Rich Grise Guest

    Just shop around for a new interface card, that comes with software.
    I did a quick search on RS-485, and all it is is the interface spec.
    What data you send is entirely up to you. These days, somebody must
    have a driver with some kind of API or library or something.

    If you're going new, you might want to look at IEE-488, or Hewlett-
    Packard's Interface Bus. ;-) Each device has its own address, and
    firmware takes care of addressing them.

    Good Luck!
  3. Tom Woodrow

    Tom Woodrow Guest

  4. KevinR

    KevinR Guest

    I am guessing he'll have trouble finding USB drivers which will work
    under DOS. Not saying there aren't any, just I have never seen any.

    Most of these type of cards have a UART and just map as com3 or
    com3 and com4.
    If you run MSD.EXE (an old DOS program which lists all sorts of info)
    then if this is the case you will have 3 or 4 comm ports listed. In
    which case, you should be able to use any off the shelf RS485 card. I
    use one made by a company called brain boxes
    They are quite helpfull, and if you email them I am sure they will
    answer any questions for you.

    If you are using a Terminate and stay resident (TSR) driver loaded
    from config.sys or autoexec.bat to handle the card then you will need
    to load this up before running MSD. If this is the case, then you will
    need to replace the driver with one designed for the new card.

    The driver is being used, because PCI cards do not map to the old
    IO/IRQ method of addressing ISA cards, which is the method DOS
    and possibly your software uses to handle serial ports.

    As far as detecting which device is talking or being talked to, the
    normal method of doing this is to have the device's address as part of
    the message which is being sent to/from the device. It's normally
    right at the beginning, or immediately following any start character.

    Yet another option is to send your data out through the standard RS232
    serial port and use an RS232 - 485 convertor box.

    Kevin R
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