Siemens CPU 410-5H Process Automation System Manual page 111

● Maximum cycle time extension
● Maximum communication delay
● Maximum inhibit time for priority classes > 15
● Minimum I/O retention time:
The monitoring start times are indicated in the highlighted boxes in Figure 12-2. These times
expire when the system enters the redundant system mode or when there is a
master/standby changeover, i.e. on the transition of the new master to RUN when the update
is completed.
The figure below provides an overview of the relevant update times.
CPU 410-5H Process Automation/CPU 410 SMART
System Manual, 10/2013, A5E32631667-AA
– Cycle time extension: The time during the update in which neither OB 1 nor any other
OBs up to priority class 15 are executed. "Normal" cycle time monitoring is disabled
within this time span.
– Max. cycle time extension: The maximum permissible cycle time extension configured
by the user.
– Communication delay: The time span during the update during which no
communication functions are processed. Note: The master CPU, however, maintains
all existing communication links.
– Maximum communication delay: The maximum permissible communication delay
configured by the user.
– Inhibit time for priority classes > 15: The time span during an update during which no
OBs (and thus no user program) are executed nor any I/O updates are implemented.
– Maximum inhibit time for priority classes > 15: The maximum permissible inhibit time
for priority classes > 15 configured by the user.
This represents the interval between copying of the outputs from the master CPU to the
standby CPU, and the time of the master/standby changeover (time at which the previous
master CPU goes into STOP and the new master CPU goes into RUN). Both CPUs
control the outputs within this period, in order to prevent the I/O from going down when
the system performs an update with master/standby changeover.
The minimum I/O retention time is of particular importance when updating with
master/standby changeover. If you set the minimum I/O retention time to 0, the outputs
could possibly shut down when you modify the system during operation.
Link-up and update
8.3 Time monitoring
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