2.2 Operating structure of a CPU
2.2.1
General
The CPU contains a standard processor with internal program
memory
. In combination with the integrated SPEED7 technology the
unit provides a powerful solution for process automation applications
within the System 300S family. A CPU supports the following modes
of operation:
n cyclic operation
n timer processing
n alarm controlled operation
n priority based processing
Cyclicprocessing 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 can 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 reac-
tion, the CPU will interrupt the cyclic processing when these high-pri-
ority events occur to react to the event. Cyclic processing will resume,
once the reaction has been processed. This means that cyclic pro-
cessing has the lowest priority
.
2.2.2 Applications
The program that is present in every CPU is divided as follows:
n System routine
n User application
The system routine organizes all those functions and procedures of
the CPU that are not related to a specific control application.
This consists of all the functions that are required for the processing
of a specific control application. The operating modules provide the
interfaces to the system routines.
Cyclic processing
Timer processing
Alarm controlled pro-
cessing
Priority based pro-
cessing
System routine
User application
VIPA System 300S Basics
Operating structure of a CPU > Applications
HB140 | CPU | 314-6CF03 | GB | 16-43 11
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