IEC 61131-3-2025 PDF

Full title and description

IEC 61131-3:2025 — Programmable controllers — Part 3: Programming languages. This international standard specifies the syntax, semantics and basic organization of programming languages and configuration elements used for programmable controllers (PLCs), covering textual and graphical languages and features to support communication and installation of control programs in automated systems.

Abstract

IEC 61131-3:2025 (4th edition) defines a unified suite of programming languages for programmable controllers, including the textual language Structured Text (ST) and the graphical languages Ladder Diagram (LD), Function Block Diagram (FBD) and Sequential Function Chart (SFC). The 2025 edition modernizes the standard with features such as UTF‑8 string support and a comprehensive annex documenting added, removed or deprecated features relative to the previous edition. It provides rules for program structure, data types, communication-related features and configuration elements to promote portability and interoperability of PLC software.

General information

• Status: Published.
• Publication date: 22 May 2025.
• Publisher: International Electrotechnical Commission (IEC).
• ICS / categories: 25.040.40; 35.240.50.
• Edition / version: 4.0 (4th edition).
• Number of pages: 518 (electronic publication).

Scope

This part of IEC 61131 specifies the syntax and semantics of programming languages intended for programmable controllers and describes configuration elements that support installation and execution of control applications in controller systems. It standardizes textual and graphical languages (ST, LD, FBD, SFC), associated data types, program organization constructs and features to facilitate communication among controllers and other automation components. The 2025 edition also documents feature changes versus the 2013 edition and introduces updates to align the standard with modern toolchains and character encoding practices.

Key topics and requirements

• Definition of the unified language suite: Structured Text (ST), Ladder Diagram (LD), Function Block Diagram (FBD) and Sequential Function Chart (SFC).
• Support for UTF‑8 strings and associated string functions (added in the 2025 edition).
• Comprehensive Annex documenting features added, removed or deprecated compared with IEC 61131-3:2013.
• Removal/deprecation of the Instruction List (IL) language (IL deprecated earlier and removed in the latest edition).
• New or clarified concurrency and synchronization constructs (examples include mutex/semaphore concepts and guidance for synchronisation of concurrent execution).
• Specifications for configuration elements to support deployment of programs into controller systems and for communication features that promote interoperability.
• Requirements and recommendations for data types, library mechanisms and conformance to enable portability across tools and vendor environments.

Typical use and users

Primary users include PLC programmers, automation and control engineers, systems integrators, tool and runtime vendors, test and validation teams, and educators teaching industrial control programming. The standard is used for developing, documenting and verifying controller programs, creating interoperable libraries and ensuring consistent behavior across development environments and runtime platforms.

Related standards

IEC 61131-3:2025 is part of the IEC 61131 series (Programmable controllers). Related parts and documents include IEC 61131-1 (general aspects and definitions), IEC 61131-2 (equipment requirements), IEC TR 61131-4 and other parts addressing communication, testing and application-specific guidance. The series is published as a bundled set for users who require multiple parts.

Keywords

programmable controller, PLC, Structured Text (ST), Ladder Diagram (LD), Function Block Diagram (FBD), Sequential Function Chart (SFC), UTF-8 strings, synchronization, conformance, IEC 61131.

FAQ

Q: What is this standard?

A: IEC 61131-3:2025 is the fourth edition of the IEC standard that defines programming languages and associated constructs for programmable controllers (PLCs). It provides formal syntax and semantics for the languages used to implement control logic.

Q: What does it cover?

A: It covers textual and graphical programming languages (ST, LD, FBD, SFC), program structure, data types, configuration elements for installing programs, communication-related features and updates such as UTF‑8 string support and documented changes relative to the 2013 edition.

Q: Who typically uses it?

A: Automation engineers, PLC developers, systems integrators, tool vendors, QA/test teams and educators rely on this standard to write, validate and exchange controller programs and libraries.

Q: Is it current or superseded?

A: IEC 61131-3:2025 is the current (published) edition as of 22 May 2025 and supersedes the previous edition (2013); it includes a list of changes and deprecations for implementers to reference.

Q: Is it part of a series?

A: Yes — it is Part 3 of the IEC 61131 series (Programmable controllers). Other parts in the series address general definitions, equipment requirements, communications and related technical reports. Many users procure multiple parts of the series together for comprehensive coverage.

Q: What are the key keywords?

A: Programmable controllers, PLC, ST, LD, FBD, SFC, UTF‑8, synchronization, conformance, IEC 61131.