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RUN Mode
4.4.1
Cyclic Program Execution
Triggering
Principle
4 - 30
With programmable controllers, cyclic program execution (program
execution level CYCLE) is the main mode.
If the CPU has completed the start-up program without errors, it then
begins cyclic program execution.
The principle of cyclic program execution (system activities):
Tr igger cycle m onitor ing tim e
Update IPC input flags
Supply process image of the
inputs ( PII)
Call cyclic user program (OB1)
Output process image of the
outputs ( PIQ)
Update IPC output flags
System activities e.g.
loading or deleting blocks
com pr essing blocks . . .
Fig. 4-6
Cyclic program execution
F r om start-up
U s e r p r o g r a m
including nesting in of
other program
execution levels
CPU 948 Programming Guide
C79000-G8576-C848-04
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