User interface OB 1
During cyclic program execution, organization block OB 1 is called
regularly as the user interface. The STEP 5 user program in OB 1 is
processed from the beginning with the block calls you have
programmed. After the system activities, the CPU starts again from
the beginning with the first STEP 5 statement in OB 1.
In OB 1, you program the calls for program, function and sequence
blocks to be executed within the cyclic program.
Interrupt points
Cyclic program execution can be interrupted by the following:
•• time-controlled program execution at block or operation
boundaries,
•• process interrupt-driven program execution via input byte IB 0 at
block boundaries,
•• interrupt-driven program execution (interrupts INT A/B/C/D, E, F,
G) at block or operation boundaries..
You specify the type of interrupt (at block or operation boundaries) in
data block DX 0 (refer to Chapter 7).
Cyclic program execution can be interrupted or aborted regardless of
the parameter setting in DX 0 as follows:
•• when a device fault or program error occurs (at operation
boundaries,
•• by operator intervention:
- stop switch, HALT (at operation boundaries),
- PG function (at checkpoints - refer to Chapter 11),
•• by the stop command STS (at operation boundaries),
•• by a power failure on the central controller or in the expansion unit
(at operation boundaries).
RUN Mode
CPU 948 Programming Guide
C79000-G8576-C848-04
4 - 31
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