Siemens S7-1200 Operating Instructions Manual page 52

Configuration and operation
4.8 Process image, type of transmission, event classes, triggers
Configuration of data points as events
Data points are configured as a static value or as an event using the "Type of transmission"
parameter (see below):
● No event (static value)
The values of data points that are not configured as an event ("Transfer after call") are
entered in the image memory of the CP and transferred to the communications partner
when it requests this value.
● Event
The values of data points configured as an event are entered in the image memory and
also in the send buffer of the CP.
The values of events are saved in the following situations:
– The configured trigger conditions are fulfilled (data point configuration > "Trigger" tab,
– The value of a status bit of the status identifiers changes.
Status identifiers: Generating an event on a status change
With data points that are configured as an event, the change to the status bit leads to an
event being generated, refer also to the section Status IDs of data points (Page 54).
Example: When the value of a data point configured as an event is updated during startup of
the station by reading the CPU data for the first time, the status "RESTART" of this data
point changes (bit status change 1 → 0). This leads to generation of an event.
Type of transmission / event classes
The following types of transmission are available:
● Transfer after call
The current value of the data point is entered in the image memory of the CP. New
values of a data point overwrite the last stored value in the image memory.
The current value at the time is transferred only after being called by the communications
partner.
● Every value triggered
The data point is configured as an event.
Each value change is entered in the send buffer in chronological order.
● Current value triggered
The data point is configured as an event.
Only the last current value is entered in the send buffer. It overwrites the value stored
there previously.
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see below)
Operating Instructions, 01/2015, C79000-G8976-C381-01
CP 1243-7 LTE