A simple state diagram is shown in Figure 20.8 An Example State Diagram.
The state diagram is implemented in FBD form in Figure 20.9 An FBD Implementation of a State Diagram Using Transition Equations. In this case the transition equations approach was used, although other methods are equally applicable. The transitions ’STA_TO_STB’, "STB_TO_STA’, ’STB_TO_STC’, and ’STC_TO_STA’ are calculated first. These are then used to update the states ’STA’, ’STB’, and ’STC’. Additional program steps could then be added to drive outputs.