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Configuration and operation
5.7 Types of transmission, event classes, triggers, status identifiers
5.7
Types of transmission, event classes, triggers, status identifiers
Classification of the data points and storage of the values
The values of data points are stored in the image memory of the CP and transferred only
when called by the operation center. Events are also stored in the send buffer and can be
transferred unsolicited. All data points are therefore classified as follows:
● No event (static value)
Data points that are not configured as an event ("Transfer after call") are entered in the
image memory (process image of the CP).
● 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 operation center.
The values of events are also entered in the send buffer of the CP.
The image memory
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 is the data buffer on the CP for storing the values of events. The send buffer
has a maximum size of 64 000 events. The configured number of events is divided equally
among all configured and enabled communications partners. The "Data buffer size"
parameter for the size of the send buffer is described in the section Communication with the
CPU (Page 47).
If a connection to a communications partner is interrupted, the values of the events are
retained in the buffer. When the connection returns, the buffered frames are sent.
The frame memory operates chronologically; in other words, the oldest frames are sent first
(FIFO principle). When the maximum number of events is reached and the frames could not
be sent, the oldest values are overwritten.
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Operating Instructions, 02/2015, C79000-G8976-C384-01
CP 1243-1 PCC
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