Siemens SIMATIC S7-1500 System Manual page 110

Basics of program processing
7.2 CPU overload behavior
If the CPU, for example, first discards a trigger for a cyclic interrupt OB, its further behavior
depends on the OB parameter "Report event overrun into diagnostics buffer": If the check
box is selected, the CPU enters the event DW#16#0002:3507 once in the diagnostics buffer
for the overload situation at this event source. The CPU suppresses additional diagnostics
buffer entries of the event DW#16#0002:3507 until all events from this source have been
post-processed.
Threshold mechanism for time error OB request
The cyclic interrupt OB parameter "Enable time error" is used to specify whether the time
error interrupt should be called when a specific overload level is reached for similar events.
You can find the OB parameter "Enable time error" in the properties of the OB in the
"Attributes" category.
When you enable the time error OB (check box selected), use the OB parameter "Event
threshold for time error" to specify the number of similar events in the queue as of which the
time error OB is called. If this parameter has the value 1, for example, the CPU enters the
event DW#16#0002:3502 once in the diagnostics buffer and requests the time error OB
when the second event occurs. The CPU suppresses additional diagnostics buffer entries of
the event DW#16#0002:3502 until all events from this source have been post-processed.
In the event of an overload, you therefore have the option of programming a reaction well
before the limit is reached for similar events and thus before the events are discarded.
The following value range applies to the "Event threshold for time error" parameter:
1 ≤ "Event threshold for time error" ≤ "Events to be queued".
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Automation system
System Manual, 12/2014, A5E03461182-AC