Glossary
Parameter
1. Variable of a STEP 7 code block
2. Variable for setting the response of a module (one or several per module). As delivered,
each module has an appropriate default setting that can be changed via configuration in
STEP 7. The parameters are divided into static and dynamic parameters.
Parameters, dynamic
In contrast to static parameters, the dynamic parameters of modules can be changed during
operation by calling an SFC in the user program, for example limit values of an analog signal
input module.
Parameters, static
Unlike dynamic parameters, static parameters of modules cannot be changed by the user
program. You can only modify these parameters by editing your configuration in STEP 7, for
example, modification of the input delay parameters of a digital signal input module.
Priority class
The S7 CPU operating system provides up to 26 priority classes (or "Program execution
levels"). Specific OBs are assigned to these classes. The priority classes determine which
OBs interrupt other OBs. Multiple OBs of the same priority class do not interrupt each other.
In this case, they are executed sequentially.
Process image
The process image is a component of the system memory of the CPU. At the start of the
cyclic program the signal states of the input modules are transferred to the process image of
the inputs. At the end of the cyclic program the process image of the outputs is transferred
as a signal state to the output modules.
PROFIBUS DP
Digital, analog and intelligent modules, as well as a wide range of field devices in
accordance with EN 50170, Part 3, such as drives or valve terminals are moved to the local
process by the automation system across distances of up to 23 km.
The modules and field devices are interconnected with the automation system via the
PROFIBUS DP field bus and are addressed in the same way as the centralized I/O.
Programming device
Programming devices are essentially personal computers suitable for industry that have a
compact design and can be transported. Their distinguishing feature is the special hardware
and software for SIMATIC programmable logic controllers.
Reduction factor
The reduction factor determines the send/receive frequency for GD packets on the basis of
the CPU cycle.
S7-300 CPU Data: CPU 315T-2 DP
Manual, 12/2005, A5E00427933-02
Glossary-7
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