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The third edition of IEC 61131-3 is approved as International Standard

The third edition of IEC 61131-3 – Programming Languages, version FDIS (Final Draft International Standard) of 2012 is approved as International Standard. This means that the 3rd edition is now official and is available as International Standard at This standard is fully upwards compatible to the second edition, i.c. IEC 61131-3; 2002.


The third edition has a long list of changes and enhancements with probably the object oriented extensions as major enhancement. These include Class, Methods and Interfaces, as well as Namespaces. The main reason to include these extensions is to link better to the scared resources of engineers in the future. With young people writing apps for the mobile world, we should better adopt to them than vice versa.


The following list shows the major changes and extensions: 

  • Editorial improvements: Structure, numbering, order, wording, examples, feature tables

  • Terms and definitions like class, method, reference, signature

  • Compliance table format


New major features

·        Data types with explicit layout

·        Type with named values

·        Elementary data types

·        Reference, functions and operations with reference; Validate

·        Partial access to ANY_BIT

·        Variable-length ARRAY

·        Initial value assignment

·        Type conversion rules: Implicit – explicit

·        Function – call rules, without function result

·        Type conversion functions of numerical, bitwise Data, etc.

·        Functions of concatenate and split of time and date

·        Class, including method, interface, etc.

·        Object-oriented FB, including method, interface, etc.

·        Namespaces

·        Structured Text: CONTINUE, etc.

·        Ladder Diagram: Contacts for compare (typed and overloaded)

·        ANNEX A - Formal specification of language elements


Deletions (of informative parts)

·        ANNEX - Examples

·        ANNEX - Interoperability with IEC 61499



·        Octal literal

·        Use of directly represented variables in the body of POUs and methods

·        Overloaded truncation TRUNC

·        Instruction list (IL)

·        “Indicator” variable of action block