315-4PN33

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.
2.2.3
Operands
The following series of operands is available for programming the
CPU:
n Process image and periphery
n Bit memory
n Timers and counters
n Data blocks
The user application can quickly access the process image of the
inputs and outputs PIO/PII. You may manipulate the following types
of data:
n individual Bits
n Bytes
n Words
n Double words
Cyclic processing
Timer processing
Alarm controlled pro-
cessing
Priority based pro-
cessing
System routine
User application
Process image and
periphery
VIPA System 300S Basics
Operating structure of a CPU > Operands
HB140 | CPU | 315-4PN33 | GB | 14-43 11