Process Image, Type Of Transmission, Event Classes, Triggers - Siemens S7-1200 TELECONTROL Operating Instructions Manual

Configuration and operation
4.9 STEP 7 configuration
Structure of the CPU scan cycle
The cycle (including the pause) with which the CP scans the memory area of the CPU is
made up of the following phases:
● High-priority read jobs
The values of input data points with the scan priority "High-priority" are read in every scan
cycle.
● Low priority read jobs
Some of the values of input data points with the scan priority "Low-priority" are read in
every scan cycle.
The number of values 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 values
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.
● Write jobs
In every cycle, the values of a certain number of unsolicited write jobs are written to the
CPU. The number of values written per cycle is specified for the CP in the
"Communication with the CPU" parameter group with the "Max. number of write jobs"
parameter. The values whose number exceeds this value are then written in the next or
one of the following cycles.
● Cycle pause time
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.
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.
4.9.7.6

Process image, type of transmission, event classes, triggers

Saving the data point values
The values of data points are stored in the image memory of the CP and transferred only
when queried by the communications partner.
Events are also stored in the frame memory (send buffer) and can be transferred unsolicited.
Data points are configured as a static value or as an event using the "Type of transmission"
parameter (see below):
● Transfer after call: No event / static value
Static values are entered in the image memory (process image of the CP).
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Operating Instructions, 10/2016, C79000-G8976-C311-02
CP 1242-7 GPRS V2