Glossary Updates12 new terms added to the glossaries · October 2, 2026, 22:44 CEST
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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.

By knowledge.aitechdoc.world · Published September 26, 2026 · Last reviewed

Source: AI TechDoc Knowledge editorial definition, based on TIA/EIA-232, TIA/EIA-485 and industrial communication practice

Definitions follow the cited standards and specifications. Where a source is a copyrighted publication, such as an ISO, IEC or EN standard, the definition is a close paraphrase, not a verbatim quotation, so as not to infringe copyright. We recommend reading the original publication. The sections “How it applies” are editorial commentary by AI TechDoc Knowledge and are not part of any standard.

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