Cpu Overload Behavior - Siemens SIMATIC S7-1500 System Manual

14.2

CPU overload behavior

Principle of CPU overload behavior
For the event scenarios considered in the following section, it is assumed that you have
assigned an OB to each event source and that these OBs have the same priority. The
second condition, in particular, is only for the sake of a simplified representation.
When an event occurs, the execution of the associated OB is triggered. Depending on the
OB priority and the current processor load, a time delay may occur before the OB is
executed when there is an overload. The same event can therefore occur once or several
times before the OB belonging to the preceding event is processed. Such a situation is
handled by the CPU as follows: In the order of their occurrence, the operating system
positions the events into the queue associated with their priority.
To control temporary overload situations, you can limit the number of pending events that
are linked from the same source. The next event is discarded as soon as the maximum
number of pending start events of a specific cyclic interrupt OB, for example, is reached.
An overload occurs when events which originate from the same source occur faster than
they can be processed.
More detailed information is provided in the following sections.
S7-1500 Automation System
System Manual, 02/2014, A5E03461182-AB
Basics of program processing
14.2 CPU overload behavior
169