Siemens S7-1200 TELECONTROL Operating Instructions Manual page 71

● Triggered: event
The values of data points configured as an event are also entered in the image memory
of the CP. The value of the event is sent unsolicited to the communications partner if this
function is enabled by the master.
The values of events are also entered in the send buffer of the CP.
The image memory, the process image of the CP
The image memory is the process image of the CP. All the current values of the configured
data points are stored in the image memory. New values of a data point overwrite the last
stored value in the image memory.
The values are sent after querying the communications partner, see "Transfer after call" in
the section "Types of transmission" below.
The send buffer (frame memory)
The send buffer of the CP is the memory for the individual values of data points that are
configured as an event. The maximum size of the send butter can be found in the section
Performance data and configuration limits (Page 13).
The configured number of events is divided equally among all configured and enabled
communications partners. For information on the configuration, refer to the parameter
"Frame memory size" in the section Communication with the CPU (Page 57).
If the connection to a communications partner is interrupted, the individual values of the
events are stored in the RAM of the CP. When the connection returns, the buffered values
are sent. The frame memory operates chronologically; in other words, the oldest frames are
sent first (FIFO principle).
If a frame was transferred to the communications partner, the transferred values are deleted
from the send buffer.
If frames cannot be transferred for a longer period of time and the send buffer is threatening
to overflow, the response is as follows:
The forced image mode
If the send buffer reaches a fill level of 80%, the CP changes to the forced image mode. New
values of events are no longer added to the send buffer but rather they overwrite older
existing values in the image memory.
When the connection to the communications partner returns, the CP changes back to the
send buffer mode as soon as the fill level of the send buffer has fallen below 50%.
CP 1242-7 GPRS V2
Operating Instructions, 10/2016, C79000-G8976-C311-02
Configuration and operation
4.9 STEP 7 configuration
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