Table of Contents
Advertisement
Glossary
Image memory principle
A TIM has a send buffer and a message image memory for buffering send messages. If a
send message is entered using the image memory principle, only a reference to the location
of the message is entered in the message image memory. Whenever the TIM has the same
message transferred to it again, before the message could actually be transmitted, only the
image is updated. The message can only be entered in the send buffer again after it has
been transmitted. As a result, it can only exist a maximum of once in the send buffer.
If the TIM finds only the reference to the image when processing the send buffer, it takes the
relevant message with its up-to-date information from the message image memory: This
spontaneous message is then transmitted according to the image memory principle.
ISDN
(Integrated Services Digital Network)
ISDN integrates various services in one transmission network. ISDN networks integrate
telephone, telefax, teletext, Datex-J, video phones and data transfer. This makes a wide
variety of digital services available to the user: Language, texts, graphics and other data.
LAN
(Local Area Network)
Local area network. Networked devices within a building or premises, < 2.4 km, no postal
restrictions. A communication network for common use by the subscribers. In contrast to
public networks, the user has legal control of the network and it is restricted spatially to a
(office) building or company premises. LANs exist with different topologies and cabling
systems. Example: Industrial Ethernet.
Local TIM
A TIM connected to an ST7cc PC or an S7 CPU over the MPI bus or Ethernet is known as a
"local TIM".
LTOP
(Line Transformer with Overvoltage Protection)
Copper dedicated lines are highly susceptible to electromagnetic interference. The coupling
of extraneous voltages can be inductive or capacitive, for example due to the effects of
lightning. Direct conductive coupling is also possible due to bad insulation.
The LTOP overvoltage protection modules limit extraneous voltage and overvoltage to a
non-critical level. The floating transformer also provides electrical isolation preventing
coupling of voltages into other cable sections. An LTOP protects persons and investment
and is therefore an indispensable safety element in private dedicated line networks.
Main and subcycle
The sequence of the polling cycle can be structured on the master TIM by assigning
individual polling stations to a main cycle or a subcycle. The subcycle is always activated at
the end of the main cycle; in other words, once all stations from the main cycle have been
318
SINAUT ST7 Station control system - System Manual
System Manual, 05/2007, C79000-G8976-C178-06
Advertisement
Table of Contents
