Maintenance
12.8 Reaction to faults in fail-safe modules and fail-safe motor starters
Distributed I/O system
256 System Manual, 09/2019, A5E03576849-AJ
Substitute value output for fail-safe modules
In the case of F-modules with inputs, if there is passivation, the F-system provides substitute
values (0) for the safety program instead of the process data pending at the fail-safe inputs.
In the case of F-modules with outputs, if there is passivation, the F-system transfers
substitute values (0) to the fail-safe outputs instead of the output values provided by the
safety program. The output channels are de-energized. This also applies when the F-CPU
goes to STOP mode. Assignment of substitute values is not possible.
Substitute values are used either for the relevant channel only or for all channels of the
relevant failsafe module depending on:
● The F-system used
● The type of error that occurred (F-I/O, channel fault or communication error)
● The F-module parameter assignment
Reintegration of a fail-safe module
The system changes from fail-safe to process values (reintegration of an F-module) either
automatically or only after user acknowledgment in the safety program. If channel faults
occur, it may be necessary to remove and reinsert the F-module. A detailed listing of faults
requiring removal and insertion of the F-module can be found in the section Diagnostic
messages of the respective F-module.
After reintegration, the following occurs:
● In the case of an F-module with inputs, the process data pending at the fail-safe inputs is
made available to the safety program again
● In the case of an F-module with outputs, the output values provided in the safety program
are transferred to the fail-safe outputs again
Additional information on passivation and reintegration
For additional information on passivation and reintegration of F-I/O, refer to the SIMATIC
Safety, Configuring and Programming
(http://support.automation.siemens.com/WW/view/en/54110126
) manual.
Behavior of the fail-safe module with inputs in the event of a communication disruption
F-modules with inputs respond differently to communication errors compared to other errors.
If a communication error is detected, the current process values remain set at the inputs of
the F-module. There is no passivation of the channels. The current process values are
passivated in the F-CPU.
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