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
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