Star Topology - Siemens SIMATIC NET Operating Instructions Manual

7.1.4

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.
Figure 7-2 Network structure with an optical star topology
Note the following guidelines:
● CH1 / CH0 must be set to "Monitor off" (S0/S8 = 1) on all OLMs connected to the
electrical star segment. This disables the 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 in the star segment directly next
to each other on a DIN rail.
● Switch on the terminating resistors (see section "Electrical RS-485 bus cables
(Page 44)") in the bus connectors at the two ends of the electrical star segment.
● If possible do not connect any bus nodes to the electrical star segment.
Optical link module
Operating Instructions, 01/2020, C79000-G8976-C270-06
Planning/configuring
7.1 Network topologies
57