Using I/O on the S7-400H
7-8
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07
Note
If the DP master interface module can detect failure of the complete DP master
system (e.g. in the case of a short-circuit), only this event is reported (“Master
system failure coming” W#16#39C3). The operating system then no longer reports
individual station failures. This allows the switch-over process between the active
and slave channel to be accelerated.
Duration of switch-over of the active channel
The maximum switch-over time is
DP error detection time + DP switch-over time + switch-over time of DP slave interface
module
You can determine the first two addends from the bus parameters of your DP
master system in STEP 7. You define the last addend from the manuals of the DP
slave interface modules concerned (Distributed I/O ET 200M and DP/PA bus
connection).
Notice
If you are using F modules, you have to set the monitoring time of each F module
larger than the failover time of the active channel in the H system. If you do not
adhere to this, F modules may fail when a failover of the active channel occurs.
Notice
The above calculation also includes the processing time in OB 70 or OB 86. Note
that the processing for a DP station must take no more than 1 ms. If more
extensive processing is required, disconnect this from the direct processing of the
OBs mentioned.
Note that a change of signal can only be detected by the CPU if the signal duration
is greater than the specified switch-over time.
With a switch-over of the complete DP master system, the switch-over time of the
slowest component applies to all DP components. A DP/PA link or Y link normally
determines the transfer time and the associated minimum signal duration. We
therefore recommend you to connect DP/PA and Y links to a separate DP master
system.
If you are using F modules, you have to set the monitoring time of each F module
larger than the failover time of the active channel in the H system. If you do not
adhere to this, F modules may fail when a failover of the active channel occurs.
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