Siemens SINUMERIK MC Commissioning Manual page 56

Safety program of the F-PLC
3.2 Program structure of the safety program (S7-1500)
Figure 3-1 Schematic structure of a safety program and/or an F-runtime group for an F-CPU S7-1500
Main safety block
The main safety block is the first F-block of the safety program that you program yourself.
You must assign an F-runtime group to the main safety block.
The main safety block is called in an F‑CPU S7‑1500 using the F-OB assigned to the F-runtime
group.
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Safety Integrated (with SINAMICS S120)
Commissioning Manual, 02/2020, A5E46305916B AB