Types Of Transmission, Event Classes, Triggers - Siemens SIMATIC NET S7-1200 Operating Instructions Manual

● Low-priority read jobs - proportion
● Cycle pause time
Duration of the CPU scan cycle
Since no fixed time can be configured for the cycle and since the individual phases cannot
be assigned a fixed number of objects, the duration of the scan cycle is variable and can
change dynamically.
5.7

Types of transmission, event classes, triggers

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 queried by the master. 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
● Event
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".
CP 1243-1 DNP3, CP 1243-1 IEC
Operating Instructions, 02/2014, C79000-G8976-C312-02
For data points of the type "Input", which are configured with the "Low priority" setting in
the data point configuration in "General > Priority in the scan cycle", the values of a part
of the PLC tags are read in every scan cycle.
The number of tags read per cycle is specified for the CP in the "Communication with the
CPU" parameter group with the "Max. number of read jobs" parameter. The tags that
exceed this value and can therefore not be read in one cycle are then read in the next or
one of the following cycles.
This is the waiting time between two scan cycles. It is used to reserve adequate time for
other processes that access the CPU via the backplane bus of the station.
Static values are entered in the image memory (process image of the CP).
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.
Configuration and operation
5.7 Types of transmission, event classes, triggers
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