Introduction into IEC 61131-3 Programming Languages

Scope

This Part specifies syntax and semantics of programming languages for programmable controllers as defined in Part 1 of this Standard.
The functions of program entry, testing, monitoring, operating system, etc., are specified in Part 1 of this Standard.

Overview and general requirements

This part of IEC 61131 specifies the syntax and semantics of a unified suite of programming languages for programmable controllers (PCs). These consist of two textual languages, IL (Instruction List) and ST (Structured Text), and two graphical languages, LD (Ladder Diagram) and FBD (Function Block Diagram). Sequential Function Chart (SFC) elements are defined for structuring the internal organization of programmable controller 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. The programming language elements defined in this part may be used in an interactive programming environment. The specification of such environments is beyond the scope of this part; however, such an environment shall be capable of producing textual or graphic program documentation in the formats specified in this part. The material in this part is arranged in "bottom-up" fashion, that is, simpler language elements are presented first, in order to minimize forward references in the text. The remainder of this subclause provides an overview of the material presented in this part and incorporates some general requirements.


Figure 3 - Combination of programmable controller language elements LD - Ladder Diagram (4.2) FBD - Function Block Diagram (4.3) IL - Instruction List (3.2) ST - Structured Text (3.3) OTHERS - Other programming languages (1.4.3)