Siemens SIMATIC S7-300 Series Reference Manual page 181

Operating system of the CPU
The operating system of the CPU organizes all functions and processes of the
CPU which are not associated with a special control task.
Parameter
1. STEP 7 code block variable
2. Variable for specifying module behavior (one or several per module). Each
module is delivered with a suitable default setting, which can be changed by
configuring the parameters in STEP 7.
There are ³ static and ³ dynamic parameters
Parameters, dynamic
Unlike static parameters, 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, but only by changing the configuration in STEP 7, for example
the input delay on a digital signal input module.
PG
³Programming device
PLC
³ Programmable controller
Priority class
The S7 CPU operating system offers a maximum of 26 priority classes (or
"program execution levels"), Diverse OBs are assigned to these classes. The
priority classes determine which OBs interrupt other OBs. If a priority class
includes several OBs, they do not interrupt each other, but are executed
sequentially.
PLC S7-300, CPU Specifications CPU 312 IFM to CPU 318-2 DP
A5E00111190-01
Glossary
Glossary-11