Programming languages for automated systems: IEC 61131-3 standard

Programming languages for automated systems are described in two complementary standards:

• IEC 61131-3 is the subject of this article;

• IEC 61499 is described in article [S 8 031] .

The CE 61131-3 standard defines, among other things, five languages that can be used for programming programmable logic controller (PLC) applications. The five languages are :

• SFC ("Sequential Function Chart"): derived from the GRAFCET language, this high-level language allows easy programming of all sequential processes;

• FBD ("Function Block Diagram"): this language lets you program graphically using blocks representing variables, operators or functions. It can be used to manipulate all types of variables;

• LD ("Ladder Diagram"): this graphical language is essentially dedicated to programming Boolean equations (true/false);

• ST ("Structured Text"): this is a high-level textual language. It can be used to program any type of algorithm of any complexity;

• IL ("Instruction List"): this low-level textual language is a one-instruction-per-line language. It can be compared to assembly language.

This article briefly presents the architecture of an automation project and introduces the notion of program, then describes in detail the syntax of the five languages of the IEC 61131-3 standard.