Technical data

Principle The system program activities are as follows:
User interface: OB 1 or FB 0 The system program calls organization block OB 1 or function block
FB 0 as the user interface regularly during cyclic program execution.
The system program processes the STEP 5 user program in OB 1 or
FB 0 from the beginning through the various block calls you have
programmed. Following the system activities, the CPU starts again
with the first STEP 5 statement in OB 1 (or in FB 0).
In OB 1, you program the calls for program, function and sequence
blocks that are to be processed in your cyclic program.
from restart
triggers the cycle time monitoring
updates the IPC flag inputs
updates the process input image
(PII)
calls the cyclic user program (OB 1
or FB 0)
User program
the other
basic processing levels
including nesting of
outputs the process output image
(PIQ)
updates IPC flag outputs
system activities, e.g.
loading or clearing blocks,
compressing blocks. . .
Fig. 4-6 Cyclic program execution
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RUN Mode
CPU 928B Programming Guide
C79000-B8576-C898-01
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