Siemens SIMATIC S7-400H - Figure 12-4 Meanings of the Times Relevant for Updates

Link-up and update
12.4 Time monitoring
S7-400H
156 System Manual, 03/2012, A5E00267695-11
● Maximum inhibit time for priority classes > 15
– 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.
● Minimum I/O retention time:
This represents the interval between copying of the outputs from the master CPU to the
standby CPU, and the time of the transition to the redundant system mode or
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.
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.
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Figure 12-4 Meanings of the times relevant for updates