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S5-95F
Diagram for the example
The user program is structured in such a way that when a signal group is passivated, the associated
program section will no longer be scanned (see Figure 18-1).
Note that the I/Os in a signal group may not be depassivated until this has been shown to be safe in
a check routine at the user level.
Preliminary interlock
program for the entire
control system
signal group 11
passivated?
Execute program section,
e.g. PB11, for controlling
burner 1
signal group 12
passivated?
Execute program section,
e.g. PB12, for controlling
burner 2
signal group 13
passivated?
Execute program section,
e.g. PB13, for controlling
burner 3
signal group 14
passivated?
Execute program section,
e.g. PB14, for controlling
burner 4
Depassivate
I/Os with FB255?
Figure 18-2. Schematic of a Structured Program Sequence
EWA 4NEB 812 6210-02
Yes
Is
No
Yes
Is
No
Yes
Is
No
Yes
Is
No
Yes
No
Rules for Failsafe Operation of an S5-95F
Depassivate signal
group with FB255
Program section for
checking process
variables and for
checking whether the
I/Os can be safely
depassivated
18-19
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