IEC 61131-3:2025

Overview

IEC 61131-3:2025 is the latest international standard published by the International Electrotechnical Commission (IEC) that defines the syntax and semantics of programming languages used for programmable controllers (PCs). As part three of the IEC 61131 series, this edition focuses on programming languages for industrial automation and control systems, establishing a unified framework for developing, structuring, and managing control software.

This 2025 revision introduces significant updates-including UTF-8 string support and comprehensive feature changes-ensuring modern applicability and enhanced interoperability of programmable controllers within automated systems. It specifies key programming languages such as Structured Text (ST), Ladder Diagram (LD), Function Block Diagram (FBD), and Sequential Function Chart (SFC), providing both textual and graphical options to meet diverse engineering needs.

Key Topics

• Unified Programming Languages: Standardizes the use of ST (textual), LD and FBD (graphical), and SFC (program organization) to enhance flexibility in program development for PCs.
• Syntax and Semantics: Defines clear rules and structures for program coding and interpretation to ensure reliability and consistency across different devices and vendors.
• Program Organization Units (POUs): Includes functions, function blocks, programs, classes, and interfaces, promoting modularity, reusability, and object-oriented features like inheritance and polymorphism.
• Configuration Elements: Addresses how programs are installed and configured within PC systems to optimize deployment and integration.
• Data Types and Literals: Defines elementary and user-defined data types, including recent inclusion of UTF-8 strings, extending data representation capabilities.
• Communication Model: Facilitates interaction between programmable controllers and other automated system components, enhancing system interoperability.
• Concurrency and Synchronization: Specifies mechanisms like mutexes and semaphores for managing parallel task execution within automation workflows.
• Compliance and Feature Tables: Includes detailed compliance requirements and a list of added, deprecated, or removed features compared to the 2013 edition to aid implementers.
• Annexes and Informative Content: Provides normative formal language specifications and informative material such as major changes for ease of transition and implementation.

Applications

IEC 61131-3:2025 serves as the cornerstone standard for engineers, developers, and integrators designing and programming industrial automation systems. Its comprehensive programming language suite supports:

• Industrial Machine Control: Creating robust control programs for manufacturing equipment and processing plants using standardized languages.
• Automation System Integration: Enabling seamless communication and consistent program behavior across programmable controllers from multiple vendors.
• Software Development and Maintenance: Facilitating modular, scalable, and maintainable software through clear programming conventions, object-oriented constructs, and configuration elements.
• Training and Certification: Establishing a global benchmark for teaching automation programming concepts and validating professional skills.
• Smart Factory and Industry 4.0: Supporting advanced automation and communication requirements necessary for modern intelligent manufacturing environments.
• Cross-industry Use: Applicable across sectors including automotive, energy, food processing, and water treatment where programmable controllers are integral.

The inclusion of UTF-8 strings and extended textual elements also boosts the capability to handle internationalization and complex data formats, addressing global industry needs.

Related Standards

• IEC 61131-1:2025 - General definitions and concepts for programmable controllers, forming the architectural foundation upon which IEC 61131-3 builds its language specifications.
• IEC 61131-2 - Covers equipment requirements and testing for programmable controllers, complementary to the programming language focus.
• ISO/IEC 10646 - International standard for Universal Character Set (UCS), referenced in Annex C for string and character literals compliance.
• IEC 61499 - Function blocks for distributed control systems, related for advanced automation architecture beyond the scope of IEC 61131-3.
• IEC 61508 - Functional safety standards relevant for programming practices when safety controllers are involved.
• IEC Electropedia and IEC Just Published - Essential IEC resources for terminology and the latest updates on standards and technical publications.

By harmonizing programming languages for PCs through IEC 61131-3:2025, industries worldwide can improve automation software portability, reduce development times, and foster innovation with standardized tools and methods.