Supplementary information
18.13 Link-up and update sequence
CPU 410 Process Automation/CPU 410 SMART
346 System Manual, 05/2017, A5E31622160-AC
Minimum duration of input signals during update
Program execution is stopped for a certain time during the update (the sections below
describe this in greater detail). To ensure that the CPU can reliably detect changes to input
signals during the update, the following condition must be satisfied:
Minimum signal duration > 2 × time required for I/O update (DP and PNIO only)
+ call interval of the priority class
+ execution time for the program of the priority class
+ update time
+ execution time for programs of higher-priority classes
Example:
Minimum signal duration of an input signal that is evaluated in a priority class > 15 (e.g.,
OB 40).
Figure 18-24 Example of minimum signal duration of an input signal during the update
For the link-up sequence, you need to decide whether to carry out a master/standby
changeover, or whether the redundant system state is to be achieved after that.
Link-up with the objective of achieving the redundant system state
To exclude differences in the two subsystems, the master and the standby CPU run the
following comparisons.
The following are compared:
1. Consistency of the memory configuration
2. Consistency of the operating system version
3. Consistency of the contents in load memory
If 1. or 2. are inconsistent, the standby CPU switches to STOP and outputs an error
message.
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