Siemens SIRIUS 3RK3 Equipment Manual page 234

Operation
6.5 Connecting to the AS-i master via AS-Interface
Failure of the total AS-i bus
In protection or test mode, the device evaluates the bus failure as a TARGET ≠ ACTUAL error, but
remains in safety mode. Calculation continues with the substitute value "0" for all AS-i slaves.
Note
Simulated AS-i slaves
On bus failure, the substitute value 0 is assumed for all slaves at the input of the logic in safety
or test mode.
Where values from output terminals of simulated slaves are used again as an input in the logic,
the input value is not derived using the monitor function but the value of the output terminal is
used. In this case, no substitute value is assumed.
Recovery / switch-on of the AS-i bus while safety mode is running
If the AS-i bus is switched on in safety or test mode or recovers after a failure, the substitute
values of the AS-i slaves are shut down and the received process image is transferred.
Because this procedure can be performed without informing the user and can therefore result
in safety-critical conditions, "restart" of the AS-i bus is controlled so that a startup test (if
configured) is performed in the input elements of the logic not only on entering safety mode but
also on the transition from the substitute value to the real value.
You will find additional information in Chapter " Failure of an AS-i slave (Page 233)."
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SIRIUS 3RK3 Modular Safety System
Equipment Manual, 07/2020, NEB926253002000/RS-AC/006