Glossary · Data, timing and communication
Serial interface
Also known as: Serial port, RS-232/RS-485 interface
German: Serielle Schnittstelle
In automation, a serial interface transmits data one bit after another over a single line or line pair, for example RS-232, RS-422 or RS-485, and is used to connect devices such as barcode readers, scales, drives or legacy controllers.
- Data and interfaces
In one sentence
A serial interface transmits data bit by bit over one line or line pair, e.g. RS-232 or RS-485, to connect devices such as scanners or drives.
Example
A weighing terminal sends weight values over RS-485 using Modbus RTU to the PLC's communication module.
How it applies
- Engineering: The physical interface (RS-232, RS-422, RS-485) must be distinguished from the Protocol (communication) used on it, such as Modbus RTU; baud rate, parity, stop bits and termination must match on both sides.
- Operation: Serial links are common in legacy equipment and retrofits, often bridged to Ethernet with gateways.
- Documentation: Connection diagrams, pin assignments and communication settings belong in the installation manual; the documentation team should state them in a table that integrators can check quickly.
- Troubleshooting: Wrong termination, missing bias resistors and mismatched settings are the most common faults.
Serial interface vs. protocol
RS-485 defines electrical signals; Modbus RTU defines the messages. Specifying only "RS-485" leaves the data exchange undefined.