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ITGlossary · Communication and monitoring
Serial Port
A communication port on a UPS used to connect and transmit signals to computers or monitoring equipment.
Technical level:Intermediate
Many UPS units have an RS-232 communication port, usually with a DB9 or RJ45 connector, through which they send status information to a computer: power failure, low battery, load level. With suitable software, the computer can shut down cleanly before the battery runs out.
On newer models, USB has largely replaced the serial port for connecting to a single computer, while a network card is preferred for multiple servers. The serial port remains useful in industrial systems, with older equipment, and for configuration or diagnostics by technicians.
A common mistake is using a generic serial cable instead of the manufacturer's cable. Pin assignments often differ, so communication fails, and in some cases the UPS may even shut down unexpectedly.
Related terms
- TransformerAn electrical component that changes voltage levels or isolates circuits.
- Transformerless UPSModern UPS design that omits bulky transformers to improve efficiency and reduce size.
- RS-232Point-to-point serial communication standard, usually on a DB9 connector, for linking a UPS to one computer over a distance of a few metres.
- USB PortA USB interface used for communication between UPS and computers.
- Dry ContactA passive relay contact used to transmit status signals without applying voltage.
- Ethernet Port (RJ45)The UPS's Ethernet network port, through which it can be monitored and controlled from any computer on the network via a browser, SNMP or shutdown software.