Networking
7-103
E Siemens AG, 2003 All rights reserved
SIMOTION C230-2, 04.2003 Edition
Rules for connecting nodes in a subnet
S Connect all nodes in the subnet “in a line”. Also integrate the PG’s and
SIMATIC HMI devices for commissioning or for maintenance work in series in
the subnet.
S If you operate more than 32 nodes in a subnet, you must link the bus segments
via RS 485 repeaters (also see the description of the RS 485 repeaters in the
manual S7-300 Automation Systems, M7-300, Module Data).
In a PROFIBUS subnet, all bus segments together must have at least one DP
Master and one DP Slave.
S Link bus segments that are not grounded and grounded bus segments via RS
485 repeaters.
S The maximum number of nodes per bus segment is reduced for each RS 485
repeater used. This means that a bus segment with an RS458 repeater may
only contain a further 31 nodes. However, the number of RS 485 repeaters
does not have any effect on the maximum number of nodes on the bus.
Up to 10 segments may be placed in a line.
S Activate the terminating resistor at the first and last node of a segment.
Components
You connect the individual nodes via the bus connector and the PROFIBUS bus
cable (also see Section 7.2). Remember to provide a bus connector with a PG
socket at the end of the subnet. This will give you the option of expanding the sub-
net if required (e.g. for a PG or SIMATIC HMI device).
For the connection between segments or for extending a wire, use RS 485
repeaters.
Terminating resistor
A cable must be terminated with a surge resistor to avoid faults as a result of re-
flected interference on the line. For this, activate the terminating resistor at the first
and last node of a subnet or a segment (see Fig. 7-2).
Make sure that the nodes where the terminating resistor is activated are always
supplied with voltage when ramping up and during operation.
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