Configuring The Safety Program; Introduction - Siemens SIMATIC PCS 7 Operating Manual

Configuring the safety program

7.1

Introduction

Fail-safe user program
Use the F-blocks supplied in a library with the S7 F-Systems optional package to create a
fail-safe user program (F program or safety program) with the CFC editor.
Note
The figure is available in its original size as appendix to the manual in the ZIP download of
the checklists.
As well as functions for programming safety functions, the F-blocks contain functions for
detecting and reacting to errors. In other words, they ensure that failures and errors are
detected and that an appropriate reaction is triggered to maintain the F-system in or switch it
to a safe state. The safe state in a fail-safe function is generally "0"; i.e. a "0" signal at an
input or output leads to disconnection.
The user program in the CPU can be created from F-and non-F blocks. The F-program is
configured in separate runtime groups.
Data transfer between the standard program and the F-program is handled using conversion
blocks. Please note that safety functions must be implemented with F-blocks consistently
from the input driver to the output driver. Standard signals may only change the state of a
safe output if the safety function is in a healthy state.
Compendium Part B - Process Safety (V8.2)
Operating Manual, 07/2016, A5E35031794-AB
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