Programming F-Systems
7.4 Structure of Safety Program in S7 F/FH Systems
Safety Engineering in SIMATIC S7
System Manual, 04/2006, A5E00109529-05
7-9
7.4
7.4
Structure of Safety Program in S7 F/FH Systems
Representation of Program Structure
The figure below shows the schematic structure of a safety program for S7 F/FH Systems. A
safety program consists of CFC charts with fail-safe blocks that are assigned to F-runtime
groups.
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Figure 7-3
Components of Safety Program in S7 F/FH Systems
Description of Program Structure
The safety program contains F-runtime groups and charts assigned to them. The charts
contain F-blocks including their parameter assignment and interconnection.
The F-runtime groups are inserted by the user at the start of an OB, preferably in a time
interrupt OB (OB 30 to OB 38).
The advantage of time interrupt OBs is that they interrupt the cyclic program execution in OB
1 of the standard user program at fixed time intervals. That is, the safety program is called
and run at fixed time intervals in a time interrupt OB.
The time interrupt OB can also contain standard runtime groups that are assigned their own
charts.
