The following example shows the response of the CPU when multiple similar events occur
faster than the CPU can process the associated OBs. In example 1, the user selected the
following parameter assignment:
Figure 2-2 Example of parameter assignment for the overload behavior
The figure below shows the processing sequence as soon as an event calls an associated
OB.
Figure 2-3 Example 1
As soon as an occurring event calls an OB, the event occupies a slot of the OB. The
occupied slot is free again as soon as the CPU has processed the event. If the CPU has not
completed processing the OB of an occurring event, additional occurring events each occupy
an additional slot of the OB during this time. As soon as this number exceeds the configured
number of events to be queued, these events are discarded and counted by the overflow
counter. When an OB which takes a long time to run is completed, the CPU creates an entry
in the diagnostic buffer and sets the overflow counter to zero (
①). After the CPU has
processed this long-running OP, the CPU then processes the OBs of the events that are
queued one after the other. At the next new occurring event, the CPU writes the previous
value of the reset overflow counter to the start information of the OB. The CPU then
processes the OB (
②).
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