Siemens SIMATIC ET 200M Operating Instructions Manual page 266

Glossary
Switch
PROFIBUS is based on a line topology. Communication nodes are interconnected by means
of a passive line, namely the bus.
By contrast, Industrial Ethernet is made up of point-to-point connections: Each
communication node is interconnected directly with one other communication node.
If a node is to be interconnected with several other communication nodes, this
communication node is connected to the port of an active network component (switch.) Other
communications nodes (including switches) can then be connected to the other ports of the
switch. The connection between a communication node and the switch remains a point-to-
point connection.
The task of a switch is thus to regenerate and distribute received signals. The switch "learns"
the Ethernet address(es) of a connected PROFINET device or of other switches, and passes
only the signals intended for the connected PROFINET device or switch.
A switch has a certain number of ports. Connect only one PROFINET device or a further
switch to any one of the ports.
SYNC
is a control command that is issued by the DP master to a set of DP slaves.
The SYNC control command is used by the DP master to instruct the DP slave to freeze the
output states at the current value. The DP slave stores the output data for the subsequent
frames, while the output states remain unchanged.
After each received SYNC control command the DP slave sets the outputs that were stored
as output dates.
Cyclic updating of the outputs will continue only after the DP master has issued the
UNSYNC control command.
System modification in RUN mode
Modifying a system in RUN mode enables you to change certain configuration settings while
the system is running. Processing is paused for only a few seconds. During this time process
outputs will retain their current values, which in process-related systems has virtually no
effect on the process itself.
A system modification in RUN mode can only be carried out in a distributed I/O scenario.
Terminating resistor
is a resistor that is used to adjust the bus connector performance. Terminating resistors are
always required at cable and segment ends.
For ET 200 the → bus connector is used to turn terminating resistors on or off.
264
Operating Instructions, 12/2008, EWA-4NEB780600602-08
ET 200M