Siemens Simatic S7-300 Technical Data Manual page 229

suitable basic factory setting which can be customized in STEP 7.
There are static and dynamic parameters
Parameters, dynamic
Unlike static parameters, you can change dynamic module parameters during runtime by
calling an SFC in the user program, e.g. 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.
PC station
See SIMATIC PC Station
PG
See Programming device
PLC
Programmable controllers (PLCs) are electronic controllers whose function is saved as a
program in the control unit. Therefore, the configuration and wiring of the unit does not
dependend on the PLC function. A programmable logic controller has the structure of a
computer; it consists of a CPU with memory, input/output modules and an internal bus
system. The I/O and the programming language are oriented to control engineering needs.
A PLC in the context of SIMATIC S7 --> is a programmable logic controller.
See CPU
PNO
See PROFIBUS International
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 part of CPU system memory. At the start of cyclic program execution,
the signal states at the input modules are written to the process image of the inputs. At the
end of cyclic program execution, the signal status of the process image of the outputs is
transferred to the output modules.
CPU 31xC and CPU 31x, Technical data
Manual, Edition 08/2004, A5E00105475-05
Glossary
Glossary-13