Step 5: Specifying The Centralized Settings For The Safety Program - Siemens SIMATIC S7 Functional Safety Manual

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2.3 Programming
2.3.2

Step 5: Specifying the centralized settings for the safety program

When the fail-safe CPU is inserted, an F-runtime group and the associated main safety block
are created by default and assigned to the CPU. An F-runtime group consists of an F-OB
(cyclic interrupt OB) that calls a main safety block FB. Additional user-specific safety
functions must then be called from this main safety block:
The first step in programming of the safety program is the main safety block. The main safety
block is an F-FB (with instance DB) that is called from the "Fail-Safe Organization Block"
(cyclic interrupt OB) assigned in each F-runtime group.
F-blocks created by the user are called from the main safety block. You can change the
calling block and the called block at any time.
After the safety program is executed, the standard user program will resume.
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S7-1200 Functional Safety Manual
Manual, 02/2015, A5E03470344-AA