ABSTRACT
The IEC 61131-3 standard defines two graphical languages, namely ladder diagrams (LD) and function block diagram (FBD), and two text-based languages, namely instruction list (IL) and structured text (ST), for use in PLC programming. The graphical languages use symbols to program control instructions, while the text-based languages use character strings to program instructions. The IEC 61131-3 standard includes an additional programming framework called sequential function charts (SFC). Sometimes SFC is categorized as an IEC 61131-3 language, but it is actually an organizational structure that coordinates the standard’s four true programming languages, i.e., LD, FBD, IL, and ST. The SFC structure is much like a flowchart type of programming framework, utilizing different languages for different control tasks and also routing control program actions. In this chapter, a brief introduction is provided to sequential function charts (SFC) including steps, transitions, SFC evolution rules, actions, action qualifiers, and action control. Then the implementation of SFC elements with up to twenty-four steps is explained in detail. In this chapter, twenty-four examples are considered to show the implementation of sequential function charts.
