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.

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