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RS232 DB9 Pinout

Stanislas BertrandStanislas Bertrand wrote 11/16/2020 at 08:52 • 2 min read • Like

It seems I always struggle with RS232 DB9 pinout. This page is to track it.

A good reference for DB9 can be found in FTDI RS232 Cable. See Datasheet page 17.

The RS232 connector (Male) has the following pinout, i.e configured as a Data Terminal Equipment (DTE).

Male DB9 RS232
Male DB9 RS232
PinTypeDescription
1InputDCD = Data Carrier Detect
2InputRXD = Receive Data
3OutputTXD = Transmit Data
4OutputDTR = Data Terminal Ready 
5GroundGND = RS232 signal ground
6InputDSR = Data Set Ready
7OutputRTS = Request To Send 
8InputCTS = Clear To Send
9Input / PowerRI = Ring Indicator

The device this adapter connects to should follow the following pinout.

The RS232 device connector is then female, configured as Data Communication Equipment (DCE).

Female DB9 RS232
Female DB9 RS232
PinTypeDescription
1OutputDCD = Data Carrier Detect
2OutputRXD = Receive Data
Aka Device Transmit pin (DT-in/DC-out)
3InputTXD = Transmit Data
Aka Device Receive pin (DT-out/DC-in)
4InputDTR = Data Terminal Ready 
5GroundGND = RS232 signal ground
6OutputDSR = Data Set Ready
7InputRTS = Request To Send
(DT-out/DC-in)
8OutputCTS = Clear To Send
(DT-in/DC-out)
9Input / PowerRI = Ring Indicator

The data flow in summarized as follow.

DTC to DCE
DTC to DCE
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