Siemens CPU 410-5H Process Automation System Manual page 61

Failure of the single-channel switched I/O
The fault-tolerant system with single-channel switched I/O responds to errors as follows:
● The faulty I/O is no longer available if an input/output module or a connected device fails.
● In certain failure situations (such as the failure of a subsystem, DP master system, or DP
The following applies to each station affected by a failure: If both DP slave interfaces or
PNIO connections are currently functional and the active channel fails, the previously
passive channel automatically becomes active. A redundancy loss is reported to the user
program when OB 70 starts (event W#16#73A3).
Once the problem is eliminated, redundancy is restored. This also starts OB 70 (event
W#16#72A3). In this situation, there is no changeover between the active and passive
channel.
If one channel has already failed, and the remaining (active) channel also fails, then there is
a complete station failure. This starts OB 86 (event W#16#39C4).
Note
If the DP master interface module can detect failure of the entire DP master system (due to
short-circuit, for example), it reports only this event ("Master system failure entering state"
W#16#39C3). The operating system no longer reports individual station failures. This feature
can be used to accelerate the changeover between the active and passive channel.
Duration of a changeover of the active channel
The maximum changeover time is
DP error detection time + DP changeover time + changeover time of the DP slave interface
CPU 410-5H Process Automation/CPU 410 SMART
System Manual, 10/2013, A5E32631667-AA
slave interface module IM153-2), the single-channel switched I/O remains available to the
process.
This is achieved by a switchover between the active and passive channels. This
switchover takes place separately for each DP or PNIO station. A distinction is made
between the following two types of failure:
– Failures affecting only one station (such as failure of the DP slave interface of the
currently active channel)
– Failures affecting all stations of a DP master system or PNIO system.
This includes unplugging of the connector at the DP master interface or at the PNIO
interface, shutdown of the DP master system (e.g. RUN-STOP transition on a CP 443-
5), and a short-circuit at the cable harness of a DP master system or PNIO system.
I/O configuration variants
4.5 Using single-channel switched I/O
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