
Network Topologies
3.2 Star Topology
SIMATIC NET PROFIBUS Optical Link Module OLM V4.0
10 Operating Instructions, 01/2013, C79000-G8976-C270-03
3.2 Star Topology
Figure 3-2 Network structure with an optical star topology
Several modules are grouped together to form an active PROFIBUS star coupler. Further
modules are connected to this via two-core fiber-optic cables. The modules of the star
coupler are interconnected via the electrical channel (electrical star segment). All OLM types
for different fiber-optic cables (plastic, PCF, glass) can be combined via the electrical star
segment.
Please note the following:
CH1 / CH0 must be set to “Monitor off” (S0/S8 = 1) on all OLMs connected to the
electrical star segment. This disables segmentation function of the RS-485 channel of this
OLM to achieve high availability of the electrical star.
Make sure that the electrical star segment is carefully wired. Keep its span as small as
possible to avoid interference in the electrical star segment that can spread to the whole
network. You can achieve this by positioning the OLMs directly next to each other on a
DIN rail.
Switch on the terminating resistors (see section 5.3) in the bus connectors
at the two ends
of the electrical star segments.
If possible do not connect any bus nodes to the electrical star segment.
To set up an active PROFIBUS star coupler, modules with one or two optical channels can
be used. To connect a DTE or an RS-485 bus segment to an active star coupler, modules
with one optical channel are adequate.
When the monitoring on the optical channels is active, the fiber-optic links are monitored by
the connected OLMs.
FOC
RS-485
Ch 1
Ch 2
SE
OLM/P11
Ch 1
Ch 2
SE
Ch 3
SE
OLM/G12
Ch 1
Ch 2
SE
OLM/G11-1300
Ch 1
Ch 2
SE
OLM/P11
Ch 1
OLM/P11
Ch 2
S
E
Ch 1
OLM/G11
Ch 2
S
E
Ch 1
OLM/G11-1300
Ch 2
S
E
Ch 1
OLM/P11
Ch 2
S
E
Ch 1
OLM/G11
Ch 2
S
E
DTE/
bus segment
DTE/
bus segment
DTE/
bus segment
DTE/
bus segment
DTE/
bus segment
Electrical star segment
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