Siemens Simatic S7-300 Technical Data Manual page 218

Glossary
Backup memory
Backup memory ensures buffering of the memory areas of a CPU without backup battery. It
backs up a configurable number of timers, counters, flag bits, data bytes and retentive
timers, counters, flag bits and data bytes).
Bus
A bus is a communication medium connecting several nodes. Data can be transferred via
serial or parallel circuits, that is, via electrical conductors or fiber optic.
Bus segment
A bus segment is a self-contained section of a serial bus system. Bus segments are
interconnected via repeaters.
Clock flag bits
flag bit which can be used to generate clock pulses in the user program (1 byte per flag bit).
Note
When operating with S7300 CPUs, make sure that the byte of the clock memory bit is not
overwritten in the user program!
Coaxial Cable
A coaxial cable, also known as "coax", is a metallic cabling system used in high-frequency
transmission, for example as the antenna cable for radios and televisions as well as in
modern networks in which high data transmission rates are required. In a coaxial cable, an
inner conductor is surrounded by an outer tube-like conductor. The two conductors are
separated by a dielectric layer. In contrast to other cables, this design provides a high
degree of immunity to and low emission of electromagnetic interference.
Code block
A SIMATIC S7 code block contains part of the STEP 7 user program. (in contrast to a DB:
this contains only data.)
Communication processor
Communications processors are modules for point-to-point and bus links.
Component-Based automation
See PROFINET CBA
Glossary-2
CPU 31xC and CPU 31x, Technical data
Manual, Edition 08/2004, A5E00105475-05