Controlling a SFC child program
Child (N); |
Starts the child program when the step is activated and stops (kills) it when the step is deactivated. |
Child (S); |
Starts the child
program when the step is activated (Initial steps of the child program are activated) |
Child (R); |
Stops (kills) the
child program when the step is activated (All active steps of the child program are deactivated) |
Alternatively, you can use the following statements in an action block programmed in ST"Structured text" A high-level language that is block structured and syntactically resembles Pascal language. In the following table, "prog" represents the name of the child program:
GSTART (prog); |
Starts the child program when the step is activated (Initial steps of the child program are activated) |
GKILL (prog); |
Stops (kills) the
child program when the step is activated (All active steps of the child program are deactivated) |
GFREEZE (prog); |
Suspends the execution of a child program |
GRST (prog); |
Restarts a program suspended by a GFREEZEcommand. |
You can also use the "GSTATUS" function in expressions. This function returns the current state of a child SFC"Sequential function chart" It can be used to program processes that can be split into steps. The main components of SFC are: - Steps with associated actions - Transitions with associated logic conditions - Directed links between steps and transitions program:
GSTATUS (prog) |
Returns the current
state of a child SFC program: 0: program is inactive 1: program is active 2: program is suspended |
-
-
When a child program is started by its parent program, it keeps the "inactive" status until it is executed (further in the cycle). If you start a child program in an SFC chart, GSTATUS will return 1 (active) on the next cycle.