Siemens CPU 31 Series Technical Data Manual page 95

Example: 50 % communication load
In your hardware configuration, you have specified a communication load of 50%. The
calculated cycle time is 10 ms. Using the above formula, the cycle time is extended by the
factor 2.
Physical cycle time depending on communication load
The figure below describes the non-linear dependency of the physical cycle time on
communication load. In our sample we have chosen a cycle time of 10 ms.
Influence on the physical cycle time
From the statistical viewpoint, asynchronous events—such as interrupts—occur more
frequently within the OB1 cycle when the cycle time is extended as a result of
communication load. This further extends the OB1 cycle. This extension depends on the
number of events that occur per OB1 cycle and the time required to process these events.
Note
Change the value of the "communication load" parameter to check the effects on the cycle
time at system runtime. You must consider the communication load when you set the
maximum cycle time, otherwise timing errors may occur.
CPU 31xC and CPU 31x, Technical Data
Manual, 01/2006 Edition, A5E00105475-06
Cycle and reaction times
5.2 Cycle time
5-9