Siemens ET 200SP Operating Instructions Manual page 64

Configuration and operation
4.5 Telecontrol communication (CP 1542SP-1 IRC)
Data points are configured as a static value or as an event using the "Type of transmission"
parameter (see below):
● Static value (no event)
Static values are entered in the image memory (process image of the CP).
Static values correspond to the following classes:
– DNP3: Class 0
– IEC: Class 2
● 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.
Events correspond to the following classes:
– DNP3: Class 1 / 2 / 3
– IEC: Class 1
The image memory, 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 being queried by the communications partner. Refer to "Transfer
after call" in the section "Types of transmission".
The send buffer
The send buffer of the CP is the memory for the individual values of data points that are
configured as an event. The maximum number is divided equally among all configured and
enabled communications partners. You configure the size of the send buffer with the
parameter "Frame memory size", see the section Communication with the CPU (Page 56).
If the connection to a communications partner is interrupted, the individual values of the
events are retained in the buffer. 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 value is 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 depending on the protocol being used:
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CP 1542SP-1, CP 1542SP-1 IRC, CP 1543SP-1
Operating Instructions, 01/2017, C79000-G8976-C426-03