plcint

Plcint is a term that appears in discussions of industrial automation to describe a lightweight, open approach to exchanging data between programmable logic controllers (PLCs) and software applications. There is no formal standard named plcint; rather, the term is used by various projects to denote a set of conventions for representing PLC data and providing APIs to read and write tag values, subscribe to changes, and serialize data for transport.

Concept and scope: In common usage, plcint aims to provide a consistent data model for standard PLC data types (BOOL, INT, REAL, etc.), simple addressing, and an event-driven model that can be implemented over multiple transports such as TCP, UDP, or message buses. The emphasis is typically on lightweight integration rather than on full automation system semantics.

Implementation and ecosystem: Several open-source and commercial projects describe plcint-style libraries for languages including C, C++, and Python. They usually offer a client API to connect to PLCs or gateway devices, enumerate available tags, perform reads and writes, and manage subscriptions for data changes. Some deployments use plcint as a bridge between plant-level PLCs and higher-level software such as SCADA, MES, or ERP systems.

Relationship to standards: plcint is not a formal standard. It is commonly used alongside established protocols and standards such as Modbus, OPC UA, and MQTT, and may require mapping of data types and addressing schemes for interoperability.

Notes: As with any integration approach, compatibility depends on the concrete implementation and the PLC hardware involved.