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RS232 Pinouts

  1. We use RJ12 for all of our RS232 interfaces (Link-2-Modbus & Link-2-PC-Serial/RS232). The diagram below shows our pin out. 

 

  1. A DB9 Female to RJ12 Female Serial/Terminal Modular Adaptor is normally needed for one to be able to connect it to the computer’s serial port. If the computer does not have a serial port, a “Serial to USB” adaptor may be used.
    DB9 Female to RJ12 Female
    Adaptor
    Serial to USB Adaptor


  1. A typical DB9 Female to RJ12 Female Adaptor pin out is outlined below

Female RJ 12 Side

DB9 Side

White

Pin 1

Pin 1

Data Carrier Detect

Black

Pin 2

Pin 2

Receive Data (RX)

Red

Pin 3

Pin 3

Transmit Data (TX)

Green

Pin 4

Pin 4

Data Terminal Ready

Yellow

Pin 5

Pin 5

Signal Ground

Blue

Pin 6

Pin 6

Data Set Ready

 

 

Pin 7

Request to Send

 

 

Pin 8

Clear to Send

 

 

Pin 9

Ring Indicator

 

  1. Therefore on the DB9 to RJ12 Adaptor, Black wire goes to #5, Yellow wire goes to #3, & Blue wire goes to #2 on the DB9 side.

 

  1. You will notice that our pin 5 is RX(in) but yet we are connecting it to Pin 3 on the DB9 which is Transmit (TX), and our pin 6 is TX (out) but yet we are connecting it to Pin 2 on the DB9 which is Receive (RX). This is correct because it should be vice versa, “TX-out to RX-in.”
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