Siemens Simatic S7-400 - Manual (Page 608)

Glossary
Glossary-2
S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07
Bus connector
A physical connection between the bus nodes and the bus cable.
Bus segment
A bus segment is a self-contained section of a serial bus system. Bus segments
are interconnected by means of
³
repeaters.
Central controller
An S7-400 consists of a central controller (CC) that can be allocated expansion
units (EU), as required. The central controller is the mounting rack that contains
the
³
CPU.
Central processing unit
³ CPU
Cold restart
³
Restart of the programmable controller and its user program, after all the
dynamic data (variables of the input/output image, internal registers, timers,
counters, etc. and the corresponding program sections) have been reset to a
specified value.
A cold restart can be automatically triggered, such as after a power failure or loss
of information in dynamic memory sections, etc., or manually by pressing the
reset key.
Common mode voltage
A voltage that is common to all inputs/outputs of a group and is measured
between this group and any reference point (usually to ground).
Communication load
This is the load on the cyclic program scanning of a CPU caused by
communication operations (for example, via
³ PROFIBUS DP).
To prevent communication operations overloading cyclic program scanning, you
can set the maximum permissible load that communication can place on the scan
cycle by parameter assignment in STEP 7.
Communication processor
Programmable module for communication tasks, such as networking,
point-to-point connection.