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
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 inter-
vals.
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 reaction, the CPU will interrupt the cyclic pro-
cessing 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.
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
Cyclic processing
Timer processing
Alarm controlled pro-
cessing
Priority based processing
System routine
User application
System 300S
+
Basics
Operating structure of a CPU > Operands
HB140 | CPU | 315-4PN23 | en | 18-02
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