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Thread: Common RS- 232C Connections.

  1. #1
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    Thumbs up Common RS- 232C Connections.

    Hi all, Just some basic cable inter-connections for RS-232 cables.

    There are two basic versions, a serial cable and a null modem cable.
    First I will give some definitions.
    DTE = Data Terminal Equipment. (e.g. a computer terminal.)
    DCE = Data Circuit Terminating Equipment. (e.g. a modem.)

    The most common serial connections for 9 and 25 pin cables are:
    Signal Name Pin No.......(9 pin).(25 pin)
    TD Transmitted Data.......3..........2
    RD Received Data ..........2..........3
    RTS Request To Send......7..........4
    CTS Clear To Send..........8..........5
    DSR Data Set Ready........6..........6
    SG Signal Ground.............5..........7
    CD Carrier Detect............1..........8
    DTR Data Terminal Ready..4.........20
    RI Ring Indicator..............9.........22

    Typical connections for DB9 cable are:
    Serial Null Modem

    ..DTE >> << DCE ............ DTE >>> <<< DTE.

    [3]TD >>>>> TD ........... [3]TD >> <<< [2]RD
    [2]RD >>>>> RD ........... [2]RD >> <<< [3]TD
    [7]RTS >>>> RTS ......... [7]RTS >> << [8]CTS
    [8]CTS >>>> CTS ......... [8]CTS >> <<[7]RTS
    [4]DSR >>>> DSR ......... [4]DTR >> << [6]DSR
    [5]SG >>>>> SG ........... [5]SG >> <<< [5]SG
    [1]CD >>>>> CD ........... [1] Not required.
    [4]DTR >>>> DTR ......... [4]DTR >> << [6]DSR
    [9]RI >>>>>> RI ........... [9] Not required.

    When two computers are hooked together, (DTEs) you have to fool each that it is connected to a DCE.
    Both your computer and STB are DTEs, hence the need for a null-modem cable to load your STB from your computer.
    Any reputable electronics outlet should carry these, or make one yourself.
    From the above information, you should also be able to make 25 to 25 or 9 to 25 cable if you have these output connectors on your DTEs.

    I trust that this takes some of the mystery away.

    Kindest Regards, Bill.

  2. #2
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    Thumbs up Re: Common RS- 232C Connections.

    Hi all,
    Just to confuse the issue of a "Null Modem Cable", there is another version that I have seen. Can't figure out why it works, but it does!!

    For 9 pin connectors:

    .........DTE >>>>> <<<< DTE

    ........ [2] >>>>> <<<<< [3]
    ........ [3] >>>>> <<<<< [2]
    ...... [7-8] .no connection. [7-8].....These joined at connector.
    ..... [1-4-6]no connection[1-4-6]....These joined at connector.
    ........ [5] >>>>> <<<<< [5]

    Kindest Regards, Bill.

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    Post Understanding RS-232 Cables

    Best Regards,
    urmans.

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    The Manager urmans's Avatar
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    Post Diagram & Wiring RS- 232 Cables.

    Best Regards,
    urmans.
    Attached Files Attached Files

  5. #5

    Re: Common RS- 232C Connections.

    When i try to upgrade my receiver thru rs232 it keeps saying that it cannot read from my receiver, but when i take it to my friends computer it works fine.Could it be that rs232 is not connected in my computer?

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    Re: Common RS- 232C Connections.

    Thanks a lot for these good posts

  7. #7

    Re: Common RS- 232C Connections.

    Quote Originally Posted by zacharias View Post
    When i try to upgrade my receiver thru rs232 it keeps saying that it cannot read from my receiver, but when i take it to my friends computer it works fine.Could it be that rs232 is not connected in my computer?
    Hello! Perhaps you have a soft using the port, i had the same problem with a graphic tablet. You must desinstall all softs using com port.
    regards.

  8. #8

    Re: Common RS- 232C Connections.

    Thank you very much my freind for your help.

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