Siemens CPU 948 - Page 163

OB 38/OB 39 call Figures 4-3 and 4-4 illustrate the principle of the OB 38 and OB 39
calls.
OB 38
OB 38
OB 39
OB 22
RUN
OB 39
Communication
start-up
Communication
start-up
Initial status: RUN
Initial status: SOFT STOP
POWER DOWN/POWER UP
POWER DOWN/POWER UP
Communication
processed
once
AUTOMATIC
WARM RESTART
Cyclic
processing
of communication
Fig. 4-3 Program execution after POWER UP
OB 1
OB 39
Interruption e.g.
by STS operation
Cyclic processing
of communication
Fig. 4-4 Program execution after a cycle interruption
STOP Mode
CPU 948 Programming Guide
C79000-G8576-C848-04
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