Technical data

1.3 The Programs in a CPU

The program existing on every CPU is divided into the following:

•• the system program

and

•• the user program.

System program

The system program organizes all the functions and sequences of the

CPU which do not involve a specific control task (refer to Fig. 1-2).

Update process image

of the inputs

Output process image

of the outputs

System

program

Call

user

processin

(inter-

faces)

Execute start-up

Handle errors

Execute communications

with the programmer

Handle communications

via 2nd serial interface

Manage memory

Fig. 1-1 Tasks of the system program

The Programs in a CPU

CPU 928B Programming Guide

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