Network Topologies
3.2 Star Topology
SIMATIC NET PROFIBUS, Optical Link Module
10 Operating Instructions, 07/2008, A2B00065774O, Edition V1.5
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:
¾ CH1 must be set to “Monitor off” (S0 = 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.
¾ 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.
¾ Switch on the terminating resistors (see section 5.3) in the bus connectors at the
two ends of the electrical star segments.
¾ 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.
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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