DB9 connector

DB9 connector, a common type of electrical connector. The term “DB9” refers to a common connector type, one of the D-Subminiature or D-Sub types of connectors. DB9 has the smallest “footprint” of the D-Subminiature connectors, and houses 9 pins (for the male connector) or 9 holes (for the female connector).

The DE-9 D-sub 9-pin connector is often mistakenly referred to as the “DB-9” connector. The “E” refers to the shell size. A “DB-25” connector has a “B” size shell, but the common nine-pin connector is smaller and has an “E” size shell.

D-SUB connector layout from SignalOrigin

Because personal computers first used DB-25 connectors for their serial and parallel ports, when the PC serial port began to use 9-pin connectors, they were often labeled as DB-9 instead of DE-9 connectors, due to an ignorance of the fact that B represented a shell size. It is now common to see DE-9 connectors sold as DB-9 connectors. DB-9 nearly always refers to a 9-pin connector with an E size shell.

Name Pin layout

DE9 (DB9)


Where are DB9 Connectors used?

  • Communications ports

The widest application of D-subs is for RS-232 serial communications, though the standard did not make this connector mandatory. RS-232 devices originally used the DB25, but for many applications the less common signals were omitted, allowing a DE-9 to be used.

Many uninterruptible power supply units have a DE-9F connector on them in order to signal to the attached computer via an RS-232 interface. Often these do not send data serially to the computer but instead use the handshaking control lines to indicate low battery, power failure, or other conditions. Such usage is not standardized between manufacturers and may require special cables.

  • Network ports

DE9 connectors were used for some token ring networks as well as other computer networks. DE-9 connectors are commonly used in CAN: female connectors are on the bus while male connectors are on devices.

  • Computer video output
  • Game controller ports

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