Siemens 6AV6651-7KA01-3AA4 - S7-1200 + KTP400 Basic Starter Kit 6AV6651-7KA01-3AA4 Benutzerhandbuch

Produktcode

6AV6651-7KA01-3AA4

Easy Book
Manual, 03/2014, A5E02486774-AF

PLC concepts made easy

4.1

Tasks performed every scan cycle

Each scan cycle includes writing the outputs, reading the inputs, executing the user program

instructions, and performing system maintenance or background processing.

The cycle is referred to as a scan cycle or scan. Under

default conditions, all digital and analog I/O points are

updated synchronously with the scan cycle using an

internal memory area called the process image. The

process image contains a snapshot of the physical inputs

and outputs on the CPU, signal board, and signal

modules.

● The CPU reads the physical inputs just prior to the execution of the user program and

stores the input values in the process image input area. This ensures that these values

remain consistent throughout the execution of the user instructions.

● The CPU executes the logic of the user instructions and updates the output values in the

process image output area instead of writing to the actual physical outputs.

● After executing the user program, the CPU writes the resulting outputs from the process

image output area to the physical outputs.

This process provides consistent logic through the execution of the user instructions for a

given cycle and prevents the flickering of physical output points that might change state

multiple times in the process image output area.