Siemens SIMATIC S7 F Manual page 203

Fail-Safe Blocks
Substitute Value
In the event of communication errors (PROFIsafe) or channel faults (e.g. wire
break), in the case of passivation and during a startup (cold or warm restart), the
substitute value 0 is made available for the associated F module driver
(F_M_DOx). 16#48 is output as the quality code (QUALITY), and the output QBAD
= 1 is set.
If the substitute value is not caused by passivation, the output PASS_OUT = 1 is
set as well to passivate other channels. In the event of an error, the output of the
substitute value has the highest priority.
Startup Characteristics
After a startup (cold restart or warm restart), communication must first be
established between the F module driver and the digital output 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. At ACK_REQ = 1 the
ACK_REI acknowledgement must follow, even if ACK_NEC = 0.
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
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)
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