Siemens SIMATIC S7 F Manual page 251

Fail-Safe Blocks
Note
In byte 0 of DIAG_1/2, the most recent error information remains stored until a new
error occurs, even if the error has already gone.
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
Fail-Safe Systems
A5E00085588-03
Description
Error in the safety data format (error due to online modification of the Safety
Program or internal CPU fault)
8-63