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16.15.3
Communication load
The operating system of the CPU provides the configured percentage of the overall CPU
processing capacity to the communication on a continuous basis (time slice technique). If
this processing capacity is not required for communication, it is made available to the other
processing.
In the hardware configuration you can specify a communication load value between 5% and
50%. The default value is 20%.
This percentage is to be interpreted as a mean value, i.e., within one time slice, the
communication portion may be significantly greater than 20%. The communication portion is
then only a few % or 0% in the next time slice.
The formula below describes the influence of communication load on the cycle time:
Figure 16-27 Formula: Influence of communication load
Data consistency
The user program is interrupted to process communications. This interruption can be
triggered after any command. These communication jobs may lead to a change in user data.
As a result, data consistency cannot be ensured over several accesses.
How to ensure data consistency in operations comprising more than one command is
described in Chapter "Consistent data".
Figure 16-28 Distribution of a time slice
The operating system takes a certain portion of the remaining time slice for internal tasks.
This portion is included in the factor defined in the tables starting at 16-3.
Example: 20% communication load
In the hardware configuration you have set a communication load of 20%.
The calculated cycle time is 10 ms.
CPU 410-5H Process Automation/CPU 410 SMART
System Manual, 10/2013, A5E32631667-AA
16.15 Cycle and response times of the CPU 410-5H
Supplementary information
277
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