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DB-9 Connector Pinout

Author: Stephen Stebbing

Close up of DB-9 male connector

The DB-9 connector is a member of the D-subminiature or D-sub family of connectors and is officially known as the DE-9 connector. It is commonly used for RS232 serial ports.

1. Diagram

DB-9 plug and socket diagram with pinouts

Note that the DTE device (eg the PC) uses the male plug and the DCE peripheral (eg the modem) uses the female socket.

2. Pinout

1DCDData Carrier Detect
2RXDReceive Data
3TXDTransmit Data
4DTRData Terminal Ready
5GNDSignal Ground
6DSRData Set Ready
7RTSRequest to Send
8CTSClear to Send
9RIRing Indicator
  • The DCE peripheral receives data on the TXD line and transmits on the RXD line.
  • For a null-modem connection, DTR is connected to DSR and RTS is connected to CTS.
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