ISPSoft User Manual 14.2 Sequential Function Chart in ISPSoft If users use sequential function chart (SFC) for programming, the content of this program format may vary according to the PLC series. This chapter contains introduction of the SFC structure. 14.2.1 Steps and Actions Every step in ISPSoft must be assigned a variable whose data type is STEP, and functions as a state flag. If the flag correspond to a step is ON, the step is active. Every symbol in AH5x0 and DVP series whose data type is STEP occupies an S device in the PLC. Please refer to operation manuals for more information about the S devices.
After a step is activated, the actions associated with the step will be executed according to the qualifiers. In ISPSoft, the actions can be modularized, and can be associated with different steps. A step can be associated with more than one action. Besides, every action has a qualifier that determines when the action is executed. In ISPSoft, an action is a program code, and can be developed by means of a ladder diagram, an instruction list, a function block diagram, or a structured text. The actions which are created are listed in the project management area.
The program editing window in which an action can be created differs from the window for a programming language in that there is no local symbol table in the program editing window in which an action can be created. In ISPSoft, the actions and the transitions in a sequential function chart share the same local symbol table. 14-4