Read Cycle - Siemens SIMATIC NET TeleControl S7-1200 CP 1243-1 Operating Instructions Manual

Configuration
4.9 Data points
● Output
– A data point of the type output can have the same index as a data point of the type
– Several data points of the type output can have the same index.
Note
Data points for the inter-station communication with a CP in another S7 station
Note that for inter-station communication, the indexes of the two corresponding data points
(data point pair) must be identical for the sending and receiving CP, see also section Partner
stations: Configuring the inter-station communication (Page 87).
4.9.6

Read cycle

Priority of the data points
The cyclic reading of the values of input data points from their assigned PLC tags on the
CPU can be prioritized.
Less important input data points do not need to be read in every CPU scan cycle. Important
input data points, on the other hand, can be prioritized for updating in every CPU scan cycle.
You can prioritize the data points in STEP 7 in the data point configuration in the "General"
tab with the "Read cycle" parameter. There you will find the two following options for input
data points:
● Fast cycle
● Normal cycle
The data points are read according to the method described below.
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.
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input.
Operating Instructions, 12/2016, C79000-G8976-C365-02
CP 1243-1