Siemens CPU 948 User Manual

In the organization blocks OB 2 to OB 9, you program the part of your
STEP 5 program to be executed when one of the process interrupts
occurs indicated by a bit in input byte IB 0.
If the corresponding OB is not loaded, program execution is not
interrupted. No interrupt-driven program processing takes place.
Note
If the I/O module no longer acknowledges when the CPU accesses
IB 0, the system program recognizes a timeout and calls the user
interface OB 28. If OB 28 is not loaded, the CPU changes to the
stop mode.
Priority of process interrupts The default setting means that PROCESS INTERRUPTS have a lower
priority than the TIMED INTERRUPTS level.
A parameter in data block DX 0 allows you to change the default so
that the PROCESS INTERRUPTS level has a higher priority than the
TIMED INTERRUPTS level.
The following priorities are set for process interrupt processing:
I 0.0
I 0.1
I 0.2
I 0.3
I 0.4
I 0.5
I 0.6
I 0.7
OB 2
OB 3
OB 4 ascending
OB 5 priority
OB 6
OB 7
OB 8
OB 9
With process interrupts, no nested execution is possible. When a
process interrupt OB has been completely processed and there are
further process interrupts pending, the system program calls the OB
with the next lower priority and processes it.
The PROCESS INTERRUPTS level is only exited when each signal
change in input byte IB 0 has been dealt with and the corresponding
OB completely processed.
Note
Process interrupt-driven program execution cannot be interrupted
by further process interrupt-driven program execution.
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CPU 948 Programming Guide
4 - 42 C79000-G8576-C848-04

Siemens CPU 948 Specifications

General

Brand	Siemens
Model	CPU 948
Category	Controller
Language	English