Siemens SIMATIC S7 F Manual page 200

Fail-Safe Blocks
Startup Characteristics
After a startup (cold restart or warm restart), communication must first be
established between the F module driver and the digital input module. In this time,
the substitute value 0 is output with the quality code (QUALITY) 16#48, and the
outputs QBAD = 1 and PASS_OUT = 1 are set as well.
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
Report Characteristics
The block has no reporting behavior.
See Also
Common Features of the Driver Blocks
Passivation and Reintegration
8-12
Description
Error in the safety data format (error due to online modification
of the Safety Program or internal CPU fault)
Fail-Safe Systems
A5E00085588-03