Siemens S7-300 appendix Token, Topology, Twisted Pair, Ungrounded, User memory, Varistor

Glossary

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

Glossary-22

CPU 31xC and CPU 31x, Technical data Manual, Edition 08/2004, A5E00105475-05