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Pinout RS-232

A Data Communications Equipment (DCE) can be interfaced to a Data Terminal Equipment (DTE) using a straight through serial cable. Typically, PC's are defined as a DTE and peripherals are defined as DCE. To interface a DCE with another DCE, or a DTE with another DTE, a null modem (or a Crossover) cable is required. The null modem simply swaps pins to convert a DCE to a DTE and vice-versa.

DB9 Male Connector
DTE
DB9 Female Connector
DCE
DB9 Male Connector DB9 Female Connector

 

9 pin 25 pin DTE DTE Signal Name DTE Direction DCE DCE Signal Name DCE Direction Description
1
8
DCD
 Data Carrier Detect
IN
DCD
 Data Carrier Detect
OUT
 Modem connected to another
2
3
RxD
 Receive Data
IN
TxD

Transmit Data
OUT
 Receives bytes into the PC
3
2
TxD
 Transmit Data
OUT
RxD
 Receive Data
IN
 Transmits bytes out of the PC
4
20
DTR
 Data Terminal Ready
OUT
DTR
 Data Terminal Ready
IN
 I'm ready to communicate
5
7
SG
 Signal Ground  
SG
 Signal Ground    
6
6
DSR
 Data Set Ready
IN
DSR
 Data Set Ready
OUT
 I'm ready to communicate
7
4
RTS
 Request To Send
OUT
RTS
 Request To Send
IN
 RTS/CTS flow control
8
5
CTS
 Clear To Send
IN
CTS
 Clear To Send
OUT
 RTS/CTS flow control
9
22
RI
 Ring Indicator
IN
RI
 Ring Indicator
OUT
 Telephone line ringing

 

DTE to DCE Interface

DTE to DCE Wiring

 

DCE to DCE Interface

DCE to DCE Wiring