Manual VIPA CPU 21x Chapter 1 Principles
HB103E - Rev. 05/45 1-15
Operating modes of a CPU
These CPUs are intended for small and medium sized applications and are
supplied with an integrated 24V power supply. The CPU contains a
standard processor with internal program memory. In combination with the
System 200V peripherals the unit provides a powerful solution for process
automation applications within the System 200V family.
A CPU supports the following modes of operation:
• cyclic processing
• timer processing
• alarm controlled processing
• priority based processing
Cyclic processing represents the major portion of all the processes that
are executed in the CPU. Identical sequences of operations are repeated in
a never ending cycle.
Where a process requires control signals at constant intervals you can
initiate certain operations based upon a timer, e.g. not critical monitoring
functions at one-second intervals.
If a process signal requires a quick response you would allocate this signal
to an alarm controlled procedure. An alarm may activate a procedure in
your program.
The above processes are handled by the CPU in accordance with their
priority. Since a timer or an alarm event requires a quick reaction the CPU
will interrupt the cyclic processing when these high-priority events occur to
react to the event. Cyclic processing will resume once the reaction has
been processed. This means that cyclic processing has the lowest priority.
General
Cyclic processing
Timer processing
Alarm controlled
operation
Priority based
processing
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