Siemens SIMATIC S7-300 Series Reference Manual page 180

Glossary
MPI
The Multipoint Interface (MPI) represents the SIMATIC S7 programming
interface, used to operate multiple nodes (Programming devices, text displays,
operator panels) on one or multiple central modules. Each station is identified by
a unique address (MPI address).
MPI address
³ MPI
Nesting depth
One block can be called from another by means of block calls. Nesting depth is
the number of ³ code blocks called simultaneously.
Non-isolated
On non-isolated input/output modules, there is an electrical connection between
the reference potentials of the control and load circuits.
OB
³Organization block
OB Priority
The CPU ³ operating system differentiates between different priority classes,
e.g. cyclic program processing, process-interrupt controlled program processing.
An OB is assigned to each one of the priority classes. ³ The S7 user can
program a reaction in these OBs. The OBs have different standard priorities
which determine the order in which they are executed or interrupted in the event
that they are activated simultaneously.
Organization block
Organization blocks (OBs) represent the interface between the operating system
of the CPU and the user program. The processing sequence of the user program
is defined in the organization blocks.
Operating mode
SIMATIC S7 automation systems know the following operating states: STOP,
³ STARTUP, RUN.
Glossary-10
PLC S7-300, CPU Specifications CPU 312 IFM to CPU 318-2 DP
A5E00111190-01