Programmable controllers - Part 3: Programming languages

IEC 61131-3:2025 specifies the syntax and semantics of programming languages for programmable controllers as defined in IEC 61131-1. This document specifies the syntax and semantics of a unified suite of programming languages for programmable controllers (PCs). This suite consists of the textual language structured text (ST), and the graphical languages, ladder diagram (LD) and function block diagram (FBD). An additional set of graphical and equivalent textual elements named sequential function chart (SFC) is defined for structuring the internal organization of programs and function blocks. Also, configuration elements are defined which support the installation of programmable controller programs into programmable controller systems. In addition, features are defined which facilitate communication among programmable controllers and other components of automated systems. This edition includes the following significant technical changes with respect to the previous edition: a) inclusion of UTF-8 strings and their associated functions; b) Annex B contains a comprehensive list of features that have been added, removed or deprecated in comparison to IEC 61131-3:2013.