Typical Mode Of Operation Of A Cpu - Siemens CPU 948 Programming Manual

Typical Mode of Operation of a CPU

Time-controlled processing
Interrupt-driven processing
Processing according to
priority
1 - 6
In addition to the cyclic processing, time-controlled processing is
also available for processes requiring control signals at constant
intervals, e.g. non-time critical monitoring functions performed every
second.
If the reaction to a particular process signal must be particularly fast, this
should be handled with interrupt-driven processing. With, for example,
a system interrupt, triggered via an interrupt generating module, you
can activate a special processing section within your program.
The types of processing listed above are handled by the CPU
according to their priority.
Since a fast reaction is required to a time or interrupt event, the CPU
interrupts cyclic processing to handle a time or interrupt event. Cyclic
processing therefore has the lowest priority.
Whether or not the time-controlled processing is more important than
the interrupt controlled processing depends, among other things, on
the particular task. For this reason, the priority of time and
interrupt-driven processing on the CPU 948 can be selected.
CPU 948 Programming Guide
C79000-G8576-C848-04