
Glossary
STEP 7 Basic V10.5
200 Getting Started, 12/2009, A5E02651459-01
Organization block
Organization blocks (OBs) are the interface between the CPU operating system and the user
program. The order in which the user program executes is specified in organization blocks.
Output
Memory area in the system memory of the CPU (process image of outputs) or connection to
an output module.
PID controller
The PID controller continuously detects the measured actual value of the controlled variable
within a control loop and compares this with the desired setpoint. The PID uses the resulting
control deviation to calculate a controller output that adjusts the controlled variable (i.e. the
variable that is to be controlled) as quickly and smoothly as possible to the setpoint.
PLC
Programmable logic controllers (PLCs) are electronic controllers whose functionality is
stored as a program on the control device. The installation and wiring of the device do not
therefore depend on the function of the PLC. A PLC is made up of at least one power supply
module, one CPU, and input and output modules.
PLC tag table
A table used to define tags valid in the entire CPU.
Process image
The signal states of the digital input and output modules are stored on the CPU in a process
image. A distinction is made between the process image input (PII) and the process image
output (PIQ).
The process image output (PIQ) is transferred by the operating system to the output
modules before the execution of the user program and before the reading of the process
image input.
The process image input (PII) is read from the input modules by the operating system before
the user program is started.
Program
A program solves a self-contained control task. It is assigned to a programmable module and
can be structured in smaller units, for example blocks.
Programming device
A compact version of a personal computer designed specially for industrial use. A
programming device (PG) is completely equipped for programming SIMATIC automation
systems.
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