Siemens SIMATIC S7 F Manual page 241

Fail-Safe Blocks
Error Handling
In the event of an error that is critical to safety, the system function SFC F_CTRL
is called. This records the event in the Diagnostic Buffer and requests a switch to
the reserve CPU if the error occurred only on the master CPU. For non-redundant
systems or a common-cause error occurring in both CPUs, the shutdown logic can
be configured to either disable the erred F-run-time group or the entire Safety
Program.
Error Information in Diagnostic Buffer
Error Code (W#16#...)
75DAH
75DCH
Fail-Safe Systems
A5E00085588-03
Description
Error in the safety data format of the input TIMEOUT (error
due to online modification of the Safety Program or internal
CPU fault)
Internal CPU fault
8-53