Siemens CP 1243-1 PCC Operating Instructions Manual page 37

Types of transmission
Depending on your CP type, you have the following transmission types 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.
After being called by the communications partner, the current value at the time is
transferred.
● Event class
The value is entered in the send buffer as an event and transferred unsolicited to the
communications partner when the trigger fires.
You will find details of the event classes and triggers in the following sections.
The type of transmission is specified for each data point in the data point configuration in
STEP 7 with the "Type of transmission" or "Event class" parameter.
Event classes
The process data of the various event classes is handled as follows:
● Every value triggered
Each value change is entered in the send buffer in chronological order.
● Current value triggered
Only the current value at the time the trigger condition was met is entered in the image
memory and overwrites the last value stored there.
Trigger
Various trigger types are available for starting event-driven transfer:
● Threshold value trigger
The value of the data point is transferred when this reaches a certain threshold. The
threshold is calculated as the difference compared with the last stored value, refer to the
section Threshold value trigger (Page 52).
● Time trigger
The value of the data point is transferred at configurable intervals or at a specific time of
day.
● Event trigger
The value of the data point is transferred when a configurable trigger signal is fired. For
the trigger signal, the edge change (0 → 1) of a trigger bit is evaluated that is set by the
user program. When necessary, a separate trigger bit can be configured for each data
point.
Resetting the trigger bit in the bit memory area / DB
If the memory area of the trigger bit is in the bit memory or in a data block, the trigger bit is
reset to zero when the data point is transferred.
Siemens Automation
CP 1243-1 PCC
Operating Instructions, 02/2015, C79000-G8976-C384-01
5.7 Types of transmission, event classes, triggers, status identifiers
Configuration and operation
37