An occurring event triggers the execution of the associated OB. 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 user program processes the OB belonging to the preceding event. The CPU handles
such a situation as follows: The operating system queues the events in the queue associated
with their priority in the order of their occurrence. The CPU then takes the oldest event for
the highest priority and processes the associated OB. After the OB has been processed, the
CPU processes the OB for the next event.
To control temporary overload situations, you can limit the number of queued events that
originate from the same source. The next event is discarded as soon as the maximum
number of pending triggers of a specific cyclic interrupt OB, for example, is reached.
Overload occurs when similar events occur faster than the CPU can process these events.
Similar events are events from a single source, such as start events for a specific cyclic
interrupt OB.
In the properties of an organization block in which an overload can occur, you can select the
response to the overload response under "Attributes" and "Event queuing".
Figure 2-1 Configuration of the overload response in the block properties
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