Technical data

Disabling interrupt-driven
processing
The system program inserts an interrupt-driven program into the
cyclic program at a block boundary or at a STEP 5 operation
boundary.
An interruption of this type can have a negative effect if a cyclic
program section has to be processed within a specific time (e.g. to
achieve a specific response time) or if a sequence of operations should
not be interrupted (e.g. when reading or writing related values).
If a section of the user program should
not be interrupted by
interrupt-driven processing, you can use the following program
procedures:
•• Program this section so that it does not contain a block change and
retain the default in DX 0 (process interrupts at block limits).
Program sections that do not contain block changes cannot be
interrupted.
•• Program the disable process interrupts (IA) operation. Enable
interrupt processing with the enable interrupts (RA) operation. No
process interrupt driven program execution can take place between
these two operations.
IA and RA are only allowed in function blocks (supplementary
operation set).
•• You can use the special functions OB 120 and OB 122 to disable
or delay the processing of process interrupts for a particular
program section.
4.5.5
Nested Interrupt-Driven and
Time-Driven Program
Execution
Priorities for interrupt and
time-driven program execution
If a process interrupt occurs during time controlled program
execution, the program is interrupted at the next interrupt point (block
or operation boundary) and the process interrupt is processed.
Following this, the time-controlled program is completed.
If a time interrupt occurs during interrupt-driven program execution,
the interrupt-driven program execution is completed first before the
time-driven program execution is started.
RUN Mode
CPU 928B Programming Guide
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