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Principle of Program Execution
3.1
Principle of Program Execution
S y s t e m p r o g r a m
f r o m s t a r t - u p
Tr i g g e r c y c l e t i m e
Up d a t e in t e r -
p r o c e s s o r c o m m .
f la g in p u t s
Up d a t e p r o c e s s
im a g e in p u t s
( PI I )
Ca l l OB1
Up d a t e p r o c e s s
im a g e o u t p u t s
( PI Q )
Up d a t e in t e r -
p r o c e s s o r c o m m .
f la g o u t p u t s
Fig. 3-1
Principle of cyclic program execution
3 - 4
You can process your STEP 5 user program in various ways.
Cyclic program execution is most common with programmable
controllers (PLCs). The system program runs through a program loop
(the cycle, refer to Section 3.4) and calls organization block OB 1
cyclically in each loop (refer to Fig. 3-1).
OB 1
Ca l l PB 2 0
BE
Us e r p r o g r a m
CPU 948 Programming Guide
C79000-G8576-C848-04
PB 20
BE
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