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ITGlossary · Communication and monitoring
RS-232
Point-to-point serial communication standard, usually on a DB9 connector, for linking a UPS to one computer over a distance of a few metres.
Technical level:Intermediate
RS-232 defines the voltage levels and signals of a serial link: on a DB9 connector the key pins on the computer side are 2 (receive), 3 (transmit) and 5 (ground). It connects only two devices to each other and works reliably over distances of up to about 15 metres.
On many UPS units the RS-232 port is used by shutdown software or by a technician for configuration. However, each manufacturer may use a different pin assignment, and some models put the serial port on an RJ45 or RJ11 jack.
A common mistake is using any DB9 cable to hand, such as a null-modem cable, instead of the one supplied with the UPS. At best there is no communication; on some models a wrong pin can even send a shutdown command.
Related terms
- Offline (Standby) UPSA UPS that leaves the load on the mains and switches to battery only when the mains fails, with a short transfer time; the simplest and cheapest topology.
- RS-485Differential serial interface over a wire pair that links many devices on one bus over long distances, usually with the Modbus RTU protocol.
- Serial PortA communication port on a UPS used to connect and transmit signals to computers or monitoring equipment.
- ModbusA communication protocol used for connecting industrial electronic devices, including UPS systems.
- SNMPA standard network protocol used to monitor and control devices like UPS systems over a network.
- USB PortA USB interface used for communication between UPS and computers.