scope:

This Part of IEC 61131 specifies syntax and semantics of programming languages for programmable controllers as defined in part 1 of IEC 61131. The functions of program entry, testing, monitoring, operating system, etc., are specified in Part 1 of IEC 61131. This Part of IEC 61131 specifies the syntax and semantics of a unified suite of programming languages for programmable controllers (PCs). This suite consists of two textual languages, Instruction List (IL) and Structured Text (ST), and two 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 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. This 3rd edition is a compatible extension of the 2nd edition. The main extensions are new data types including reference and object oriented features of classes and function blocks. The manufactures may chose and implement any consistent subset of features defined in this part; i.e. all features are normative but not mandatory. 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 standard; however, such an environment shall be capable of producing textual or graphic program documentation in the formats specified in this standard. The material in this Part is mainly arranged in "bottom-up" fashion, that is, simpler language elements are presented first, in order to minimize forward references in the text. This Part of IEC 61131-3 does not include any provisions for the harmonization with IEC 61499 - Function Blocks.