Siemens SIMATIC S7 F Manual page 187

Safety
Changes to the addresses or symbolic names of signals can be recognized by the
change to the ADDR_CODE parameter of the relevant F channel driver
(F_CH_xx).
Changes to the network configuration in NetPro can be recognized by the change
to the CRC_IMP parameter of the relevant F communication blocks (F_RCVxx and
F_SENDxx).
You can find rules and information on how to proceed in the case of changes to the
Safety Program in the section entitled "Operation and Maintenance, Modifying the
Safety Program".
Fail-Safe Systems
A5E00085588-03
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