Lenze PLC Designer PLC Designer (R3-1) - Manual (Page 776)

L-force | PLC Designer
General Editors
774 DMS 4.1 EN 03/2011 TD29
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External event: The task will be started as soon as the system event, which is defined
in the Event field, occurs. It depends on the target, which events will be supported and
offered in the selection list. (Not to be mixed up with system events.
Difference between Status and Event:
The specified event being TRUE fulfills the start condition of a status driven task,
whereas an event driven task requires the change of the event from FALSE to TRUE. If
the sampling rate of the task scheduler is too low, rising edges of the event may be left
undetected.
The following example illustrates the resulting behaviour of the task in reaction to an
event (green line):
At sampling points 1-4 (magenta) tasks of different types show different reaction:
Behaviour at point: 1 2 3 4
Status no start start start start
Event no start start no start no start
Obligatory Entries depending on task choice:
Interval (obligatory for Type 'cyclic' resp. 'triggered by external event' if the event
requires a time entry): the period of time, after which the task should be restarted. If
you enter a number, then you can choose the desired unit in the selection box behind
the edit field: milliseconds [ms] or microseconds [µs]. Inputs in [ms]-format will be
shown in the TIME format (for example "t#200ms") as soon as the window gets
repainted; but you also can directly enter the value in TIME format. Inputs in [ms] will
be displayed as a pure number (for example "300").
Event (obligatory for Type 'event'
or 'triggered by external event' ): a global variable
which will trigger the start of the task as soon as a rising edge is detected. Use button
... or the input assistant <F2> to get a list of all available global event variables.
Note: If the event that is driving a task stems from an entry, there must be at least
one task which is not driven by events. Otherwise the I/Os will never get updated
and the task will never get started.