Siemens SIMATIC CPU 410 System Manual page 72

I/O configuration variants
6.5 Using single-channel switched I/O
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).
There is also complete station failure if an IM fails in an S2 configuration. This starts OB 86
(event W#16#39C4).
Note
If the external DP master interface module can detect failure of the entire DP master system
(due to a 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/PN error detection time + DP/PN changeover time + changeover time of the DP slave
interface/PNIO interface
You can determine the first two values from the bus parameters of your DP master system or
PNIO system in STEP 7. You determine the last two values using the manuals of the DP
slave interfaces or PNIO interfaces in question.
Note
When using fail-safe modules, always set a monitoring time for each fail-safe module that is
longer than the changeover time of the active channel in the fault-tolerant system. If you
ignore this rule, you risk passivation of the fail-safe modules during the changeover of the
active channel.
You can use the Excel file "s7ftimea.xls" to calculate the monitoring and reaction times. The
file is available at the following address:
http://support.automation.siemens.com/WW/view/en/22557362
Note
Please note that the CPU can only detect a signal change if the signal duration is greater
than the specified changeover time.
When there is a changeover of the entire DP master system, the changeover time of the
slowest DP component applies to all DP components. A DP/PA link or Y-Link usually
determines the changeover time and the corresponding minimum signal duration. We
therefore recommend that you connect DP/PA and Y-Links to a separate DP master system.
72
CPU 410 Process Automation/CPU 410 SMART
System Manual, 05/2017, A5E31622160-AC