scope:

This part of IEC 61131 specifies the syntax and semantics of programming languages for pro- grammable controllers as defined 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 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 programma- ble controller programs into programmable controller systems. In addition, features are defined which facilitate communication among programmable control- lers and other components of automated systems.