What pins on RJ45 connector are recieve/transmit?

Posted on 2004-11-09
Medium Priority
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: http://www.experts-exchange.com/Hardware/Q_21199076.html, was ended prematurely.
Question by:jayrod
  • 3
  • 2

Expert Comment

ID: 12534651
Check this link, it spells your RJ45 to RS232 issue out pretty clearly.

LVL 69

Expert Comment

ID: 12534663
Pins 1,2,3, and 6 are used: http://yoda.uvi.edu/InfoTech/rj45.htm
LVL 69

Expert Comment

ID: 12534797
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
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Author Comment

ID: 12537625
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

Callandor earned 1000 total points
ID: 12538338
Maybe this diagram is better: http://www.filibeto.org/sun/lib/hardware/netra_t1-105/netra_t1_serial_pinouts.html

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

Author Comment

ID: 12543660
Thanks Callandor, I think that is exactly what I needed.

Appreciate the help.

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