Doubt regarding sequential function chart
What does PNP in a step represent in a sequential function chart
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Sequential function chart (SFC) is a graphical language for depicting the sequential behavior of a control system. It is used for defining time- and event-driven control sequences. A sequence is shown in flow-chart form, using steps, transitions and selection nodes.
P1 (pulse rising edge) is executed one time. Then Next Step(S2) becomes active and equation N is
executed as long as the transition condition Tr2 not is fulfilled. When Tr2 is fulfilled P0
(pulse falling edge) is executed one time S2 is inactivated. The sequence continues with P1 in
step S1 and so on.
P1 is executed ONCE at the start of the Step
N is executed Normally while the Step is active
P0 is executed ONCE at the end of the Step
Note that P0 may not always be executed, especially if your SFC sequence is reset while a step is active. Do not rely on P0 actions always being executed. So for example .....
P1 Variable := True;
P0 Variable := False;
N Variable := StepName.X;