IEC 61131-3 PLC Programming in 2026: ST, FBD, LD, SFC, IL, CFC Compared
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IEC 61131-3 PLC Programming in 2026: ST, FBD, LD, SFC, IL, CFC Compared
still defines the lingua franca. The standard's five normative languages , Ladder Diagram (LD), Function Block Diagram (FBD), Structured Text (ST), Instruction List (IL), and Sequential Function Chart (SFC) , cover almost every controller you will see on a plant floor, and PLCopen's
Detail
adds a sixth for continuous processes. This 2026 refresh walks through each language, what changed since the 2024 edition of this article, and which language to reach for in a modern brownfield retrofit on
The third edition (2013) deprecated IL, and the fourth edition (IS 2025) reinforced the recommendation to use ST instead; no new project should start in IL in 2026.
ST is now the default high-level language, with object-oriented features (methods, namespaces, structured types) refined in the 4th edition.
LD and FBD remain dominant for discrete I/O and process loops; SFC structures batch, mode-of-operation, and any state-driven sequence.
Vendor IDEs (Studio 5000, TIA Portal V20, GX Works3, Sysmac Studio) now treat ST as a first-class citizen with full OOP, refactoring, and OPC UA companion-spec support.
In 2026 the six IEC 61131-3 languages still cover the same control problems, but the recommended mix has shifted: ST for math, LD for wiring, FBD for loops, SFC for sequences, with IL on legacy support only.
The third edition (IEC 61131-3:2013) already marked Instruction List as legacy, and mainstream IDEs have stopped generating IL by default. Treat existing IL as maintenance-only and port to ST on the next service window.
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