ISPSoft User Manual

ISPSoft User Manual
12.1 Knowing Sequential Function Charts
12.1.1 Structure of a Sequential Function Chart
A sequential function chart is one of the five languages defined by IEC 61131-3 standard. It is a
powerful graphical technique for describing the sequential behavior of a control program.
A sequential function chart and its corresponding flowchart are shown below. The main components
of a sequential function chart are steps with associated actions, transitions with associated logic
conditions, and directed links between steps and transitions.
12.1.2 Principle of a Sequential Function Chart
A sequence in a sequential function chart is depicted as a series of steps shown as rectangular
boxes connected by vertical lines. Each step represents a particular state of the system being
controlled. A transition is associated with a condition which, when true, causes the step before the
transition to be deactivated and the step that follows the transition to be activated.
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