Siemens CPU 948 User Manual

1.2 Typical Mode of Operation of a CPU
Mode of operation of a CPU The following modes of operation are possible in a CPU:
Cyclic processing This is the main part of all activities in the CPU. As the name already
says, the same operations are repeated in an endless cycle.
Cyclic processing can be divided into three main phases, as follows:
Phase Sequence
1
All the input modules assigned to the
CPU are scanned by the system
program and the values read in are
stored in the process image of the
inputs (PII).
2
The values contained in the PII are
processed by the user program and the
values to be output are entered in the
process image of the outputs (PIQ).
3
The values contained in the process
image of the outputs are output by the
system program to the output modules
assigned to the CPU.
Cyclic processing
Interrupt-driven processing
Time-controlled processing
1. 2. 3.
Read in process image
of the inputs
Output process image
of the outputs
&
&
=
1
I1.5
I1.6
I1.4
I1.3
Q3.1
Evaluate input signals,
set output signals
Input I 1.3
Input I 1.4
Input I 1.5
Output Q 3.1
Output Q 2.0
Output Q 4.7
CPU Process
Typical Mode of Operation of a CPU
CPU 948 Programming Guide
C79000-G8576-C848-04
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Siemens CPU 948 Specifications

General

Brand	Siemens
Model	CPU 948
Category	Controller
Language	English