Siemens Simatic S7-300 CPU 31xC and CPU 31x S7-300 - Manual (Page 238)

Glossary
CPU 31xC and CPU 31x, Technical data
Glossary-22
Manual, Edition 08/2004, A5E00105475-05
Token
Allows access to the bus for a limited time.
Topology
Structure of a network. Common structures include:
•
Bus topology
• Ring topology
• Star topology
• Tree topology
Transmission rate
Data transfer rate (in bps)
Twisted Pair
Fast Ethernet via twisted-pair cables is based on the IEEE 802.3u standard (100 Base-TX).
The transmission medium is a 2x2 wire, twisted and shielded cable with a characteristic
impedance of 100 ohms (AWG 22). The transmission characteristics of this cable must meet
the requirements of category 5 (see glossary).
The maximum length of the connection between end device and network component must
not exceed 100 m. The ports are implemented according to the 100 Base-TX standard with
the RJ-45 connector system.
Ungrounded
Having no direct electrical connection to ground
User memory
User memory contains the code blocks / data blocks of the user program. User memory can
be integrated in the CPU, or stored on plug-in Memory Cards or memory modules. However,
the user program is principally processed from the RAM of the CPU.
User program
In SIMATIC, a distinction is made between the operating system of the CPU and user
programs. The user program contains all instructions and declarations, as well as signal
processing data that can be controlled by the plant or the process. It is assigned to a
programmable module (for example CPU or FM) and can be structured in smaller units
(blocks).
See Operating system
See STEP 7
Varistor
Voltage-dependent resistor