What pins on RJ45 connector are recieve/transmit?

Posted on 2004-11-09
Last Modified: 2008-03-17
Hello all,

I have an RS232 connector as follows:

3 > TD
5 > RD
7 > RTS
9 > CTS
11 > DSR
12 > RCVRDY -
13 > SIG GND
14 > DTR
19 > RESET -

Now, I need to connect the RS232 pins 3 and 5 (transmit and receive respectively) to an RJ45 connector. I need pin 3 as Transmit and 5 as Receive from the RS232 to connect to the RJ45 so I can connect it to my sniffer to capture data.

What pins do these connect to on the RJ45 connector?

Reference question:, was ended prematurely.
Question by:jayrod
    LVL 7

    Expert Comment

    Check this link, it spells your RJ45 to RS232 issue out pretty clearly.

    LVL 69

    Expert Comment

    Pins 1,2,3, and 6 are used:
    LVL 69

    Expert Comment

    Here are the pin matchups from the original question:

    RJ 45 Jack <->  DB9F

    CTS 9  <-> 7 RTS
    DTR 7 <-> 1 DCD
    GND 6 <-> 5 GND
    TX  5 <-> 2 RX
    RX 4 <-> 3 TX
    DCD 3 <-> 4 DTR
    RTS 1 <-> 8 CTS
    LVL 3

    Author Comment

    tt, you left no link :)


    The real problem I have, is that I have a single wire (not pair) on the RS232 for TX and a single wire for RX. On the RJ45, ALL references to it that you provided me show a TX + and TX - and RX + and RX -.

    I can't map that TX on the RS232 to two wires (one pair) on the RJ45.

    Does that clear up my problem?

    Thanks for all the comments.
    LVL 69

    Accepted Solution

    Maybe this diagram is better:

    RS232         RJ45
    pin5 (CTS) -> pin1 (RTS)
    pin6 (DSR) -> pin2 (DTR)
    pin3 (RXD) -> pin3 (TXD)
    pin2 (TXD) -> pin6 (RXD)
    LVL 3

    Author Comment

    Thanks Callandor, I think that is exactly what I needed.

    Appreciate the help.

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