DB9 Connector

DB9 is a commonly known connector used in Serial Asynchronous Data Transmission that are are designed to work with the EIA/TIA 232 serial interface standard. RS-232 (Recommended Standard 232) is the standard for establishing serial data transfer between DTE(Data Terminal Equipment) and DCE(Data Circuit-terminating Equipment).

The D-sub series of connectors was invented by ITT Cannon in 1952.

The letter A to E denotes the shell size, followed by the number of pins. Male(M) or Female(F) denotes the gender of the part.

Each shell size corresponds to a certain number of pins or sockets i.e. A with 15, B with 25, E with 9, etc. For example, DB-25 denotes a D-sub with a 25-position shell size and a 25-position contact configuration. In DB9 it denotes 9 position shell and 9 contact terminals.

The DB style connector is a common connector used in many computer, audio/video, and data applications.The connector gets its name from its trapezoidal shape that resembles the letter "D".

In the name, DB stands for D-Sub-miniature or D-sub but its actual name is DE-9. Db-xx is now commonly used for all serial connectors and in today's market DE-9 connectors are sold as DB-9 connectors which instead of its correct terminology.

A DB9 connector has 9 pins arranged in two rows as shown in figure having 5 pins in top row and remaining in the bottom.

It is also known as COM port and is used to interface device with data rate less than 20kbps.

DB9 ports were common earlier but now with introduction to usb, firewire, etc newer computers are being built without DB9 connectors. DB9 male connector were commonly used in PC.

DB9 connector supports full-duplex data transfer.

Earlier Apple Macintosh models used DE9. Due to its large size and high manufacturing cost miniature DIN connectors are used.

There are DB9-DB25 adapters/converters for easy conversion of a DB9 into DB25 connection, and vice versa. Similarly, converters for DB9 to other kinds of connectors are available.

Pin Description

Pin number	Name	Abbrevation	Direction
1	Carrier Detect(Received line signal detector)	CD	In
2	Receive Data	RXD/RX/RD	In
3	Transmit Data	TXD/TX/TD	Out
4	Data Terminal Ready	DTR	Out
5	Signal Ground	GND	-
6	Data Set Ready	DSR	In
7	Request To Send	RTS	Out
8	Clear To Send	CTS	In
9	Ring Indicator	RI	In
	Shield	-	-

Below Diagram shows pin Description of DB9 Male connector: DB9 Connector Pin Diagram

Electrical specifications

1. Operation voltage: 250 VAC max
2. Current rating: 3 Amps max
3. Contact resistance: 20 mOhms max
4. Insulation resistance: 3000 MOhms min at 1000 VDC between
5. Dielectric withstanding voltage: 1000 VAC min rms (sea level)
NOTE: This specifications changes with different manufacturers, requirements, etc.