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anyone familiar with rs232?

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  • 15-10-2014 4:51pm
    #1
    arctan
    Closed Accounts Posts: 354 ✭✭


    Ok, problem is, we have a modem, with an rs232 connection (25 pin), going to a piece of equipment.

    the kicker is, this piece of equipment only uses:
    1:screen
    2: RD
    3:TD
    5:GND

    that's it ...

    as you can see straight off there are no carrier detect pins etc... activated by the connecting equipment.

    so ...

    how do we wire up the connector to the modem to fool it into thinking it has a connected peripheral and will send and receive traffic ?


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    #2
    jtceltic
    Registered Users Posts: 28 ✭jtceltic


    Hi Arctan,
    I used a US robotics modem before to connect to equipment, it used a 25 way plug so I had to short out cores 4,5 and 20 to simulate at connection


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    #3
    jtceltic
    Registered Users Posts: 28 ✭jtceltic


    Hi Arctan,
    I used a US robotics modem before to connect to equipment, it used a 25 way plug so I had to short out cores 4,5 and 20 to simulate at connection, Pin 2 & 3 was the RD and TD and pin 7 was Ground


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    #4
    stimpson
    Registered Users Posts: 7,815 ✭✭✭stimpson


    This is probably what you need:

    http://www.root6.com/blog/index.php/2012/09/rs232-fifty-years-old-some-notes/

    Check out the 3 pin null modem near the bottom.


  • Options
    #5
    arctan
    Closed Accounts Posts: 354 ✭✭arctan


    thanks guys,

    still to go through them, the 3wire null config in that link, that's exactly what we tried, except we have

    CTS
    RTS
    DSR : Shorted together

    and

    DCD
    DTR: shorted together

    wheras on the site, it says it should be

    CTS
    RTS : Shorted together

    and

    DSR
    DCD
    DTR : shorted together

    would this make a difference?


  • Options
    #6
    glynf
    Registered Users Posts: 3,387 ✭✭✭glynf


    arctan wrote: »
    thanks guys,

    still to go through them, the 3wire null config in that link, that's exactly what we tried, except we have

    CTS
    RTS
    DSR : Shorted together

    and

    DCD
    DTR: shorted together

    wheras on the site, it says it should be

    CTS
    RTS : Shorted together

    and

    DSR
    DCD
    DTR : shorted together

    would this make a difference?


    That is the pin out for a 9 pin, have a look here-it may be different for a 25 pin.
    I have to use 9 pin null leads occasionally to connect a PC's serial port to connect to CCTV matrix', and use an off the shelf 9 pin Startech lead. They should have a 25 pin cable, or a converter that will do.


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    #7
    arctan
    Closed Accounts Posts: 354 ✭✭arctan


    sorry, forgot to mention that it is actually a 9 pin into the piece of equipment, its 25 on the modem, they have a 25 to 9 converter in place, so in theory, the 9 pin null should work ?


  • Options
    #8
    glynf
    Registered Users Posts: 3,387 ✭✭✭glynf


    arctan wrote: »
    sorry, forgot to mention that it is actually a 9 pin into the piece of equipment, its 25 on the modem, they have a 25 to 9 converter in place, so in theory, the 9 pin null should work ?

    Should do, you can get a 25>9 pin null modem cable as well.


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