Siemens Automation System S7-400 - Manual (Page 118)

Networking
5-20
Automation System S7-400 Hardware and Installation
A5E00850741-01
Connecting Bus Cables to Bus Connectors ( 6ES7972-0B.20 ...)
For detailed information on how to connect a bus cable to a bus connector, refer to
the SIMATIC NET Profibus Networks manual.
Connecting the Bus Connector
To connect the bus connector, proceed as follows:
1. Plug the bus connector into the module.
2. Screw the bus connector into the module.
3. If the bus connector is located at the beginning or end of a segment, you must
switch on the terminating resistor.
on
off
on
off
Terminating
resistor
switched on
Terminating resistor
not switched on
Figure 5-12 Switch on terminating resistant
Ensure that power is always applied to the stations at which the terminating resistor
is situated, during startup and operation.
Removing the Bus Connector
With a looped-through bus cable you can remove the bus connector from the
PROFIBUS-DP interface at any time, without interrupting data traffic on the bus.
!
Warning
Interference to the data traffic on the bus is possible.
A bus segment must always be terminated with the terminating resistor at both
ends. This is not the case, for example, when the last slave with bus connector is
not under power. Since the bus connector is powered by the station, the
terminating resistor has no effect.
Ensure that the stations at which the terminating resistor is switched on are always
under power.