DB9 connector

DB9 connector

The DB9 (originally DE-9) connector is an analog 9-pin plug of the D-Subminiature connector family (D-Sub or Sub-D).

The DB9 connector is mainly used for serial connections, allowing for the asynchronous transmission of data as provided for by standard RS-232 (RS-232C).

DB9 plugs

Note that there are DB9-DB25 adapters for easily converting a DB9 plug into a DB25, and vice versa.


Pin number Name
1 CD - Carrier Detect
2 RXD - Receive Data
3 TXD - Transmit Data
4 DTR - Data Terminal Ready
5 GND - Signal Ground
6 DSR - Data Set Ready
7 RTS - Request To Send
8 CTS - Clear To Send
9 RI - Ring Indicator
Ask a question
CCM is a leading international tech website. Our content is written in collaboration with IT experts, under the direction of Jeff Pillou, founder of CCM.net. CCM reaches more than 50 million unique visitors per month and is available in 11 languages.


This document, titled « DB9 connector », is available under the Creative Commons license. Any copy, reuse, or modification of the content should be sufficiently credited to CCM (ccm.net).