Chapter 14 Sequential Function Chart 14.2.2 Transitions When a transition is true, the active step immediately before the transition becomes inactive and the step immediately after the transition becomes active. A transition can be true anytime, but for a transition to activate the step following it, the step preceding it must be active when the transition is true. In ISPSoft, a transition can be a Boolean device or symbol, or a program code. If a transition is a logical operation, users can create a transition program, and assign the program to the transition. The transition programs which are created are listed in the project management area.
The programming languages which can be used to create transition programs include ladder diagrams, instruction lists, function block diagrams, and structured texts. The Boolean state in a transition program must be sent to a symbol name which is the same as the transition program name, whether the programming language used to create the transition program is a ladder diagram, an instruction list, a function block diagram, or a structured text. The symbol does not need to be declared. However, if there is a symbol name in a symbol table which is the same as a transition program name, an error occurs when the program is compiled. Besides, 14-7