Siemens Simatic M7-400 Reference Manual page 618

Glossary
Non-isolated
In the case of non-isolated input/output modules, the reference potentials of the
control and load circuit are electrically connected.
OB
³ Organization block
Organization block
Organization blocks (OBs) form the interface between the operating system of
the CPU and the user program. The order in which the user program is
processed is defined in the organization blocks.
Operating mode
The SIMATIC S7 programmable controllers have the following operating modes:
STOP, ³ STARTUP, RUN and STOP.
Operating system
The operating system of the CPU organizes all functions and processes of the
CPU that are not tied to a specific control task.
Parameters
1st tag of a ³ logic block
2nd tag for setting the characteristics of a module (one or more per module).
When delivered to the customer, each module has a practical basic setting for its
parameters, which the user can modify in STEP 7.
PG
³ Programming device
PLC
³ Programmable controller
Point-to-point connection
Only two nodes are physically linked with one another in a point-to-point
connection. This type of communication link is used if the use of a
communication network is not recommended or when, for example, different
types of partners, such as a PLC and a process computer, are to be connected.
Glossary-12
S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07