Where are DB9 Connectors used?
2.1 Communication ports
The most widespread use of D-subs connectors is for RS-232 serial communications, although the standard does not mandate such connectors. RS-232 devices originally used DB25, but for many applications, the less common signals were omitted, allowing the use of DB9 female and male connectors.
Many uninterruptible power supply units are equipped with DB9 connectors to send signals to a connected computer through the RS-232 interface. These typically do not send data serially to the computer, but instead use a handshake control line to indicate low battery, power failure, or other conditions. However, this use is not standardized between DB connector manufacturers and may require special cables.
2.2 Network port
DE9 connectors are used for some token ring networks as well as other computer networks. DB9 connectors are usually used for CAN: DB9 female connectors are located on the bus, while DB9 male connectors are located on the device.
2.3 Computer video output, game controller port
