Bus Topology - Siemens SIMATIC NET Operating Instructions Manual

Planning/configuring
7.1 Network topologies
7.1.3

Bus topology

In a bus (linear) structure, the individual PROFIBUS OLMs are connected by two-fiber
cables.
At the beginning and at the end of a line, modules with one optical channel are adequate, in
between modules with two optical channels are necessary.
Figure 7-1 Network structure with an optical bus topology
Note
When using the OLM / P22 or OLM / G22, a further end device or bus segment can be
connected to CH0.
To establish individual point-to-point connections, you can use two modules each with one
optical channel.
The bus topology can be implemented with and without fiber-optic link monitoring. Use of
fiber-optic link monitoring is recommended in homogeneous OLM networks (factory default).
Please note that for correct operation, the following conditions must be kept to when
configuring the network:
● The parameter MIN TSDR described in the PROFIBUS standard EN 50170 /2/ must be
set to a value ≥ 11 on all end devices. This is usually the case but should be checked if
permanent communication problems occur.
● Choose bus node addresses as low as possible when configuring your network, to reduce
master timeouts that may occur due to disruptions.
You will find information on changing the setting in the documentation supplied by the
manufacturer of your end device.
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Operating Instructions, 01/2020, C79000-G8976-C270-06
Optical link module