Siemens SIMATIC NET PROFIBUS manual Star topology, Network structure in an optic star topology

3 Network Topologies 3.2 Star topology

3.2 Star topology

Electrical star segment

R	T
CH 2

1
CH	S0 = 1

OLM/P11

CH 2
T	R

1
CH	S0 = 1

OLM/G12

CH 2		CH 3
T	R	T	R

1
CH	S0 = 1

OLM/G11-1300

CH 2
T	R

1
CH	S0 = 1

OLM/P11

CH 2
T	R

RS 485 bus line

Optical fiber

R	T
CH 2

OLM/P11

CH 1

Terminal unit / bus segment

R	T
CH 2

OLM/G11

CH 1

Terminal unit / bus segment

R	T
CH 2

OLM/G11

CH 1

Terminal unit / bus segment

R	T
CH 2

OLM/G11-1300

CH 1

Terminal unit / bus segment

OLM/P11

CH 1

Terminal unit / bus segment

Fig. 3: Network structure in an optic star topology

Several modules are combined to form an active PROFIBUS star coupler. Other modules are connected to this by dual-fiber optical fiber lines. The modules of the star coupler are connected to one another via the electrical port (electrical star segment).

All OLM types for different fiber types (plastic, PCF, glass) can be combined using the electrical star segment.

Please note:

CH1 in mode ”Monitor off“ (S0 = 1) must be activated on all OLMs which are connected to the electrical star segment. This deactivates the segmenting function of the RS 485 port on these OLMs, providing a high degree of availability of the electrical star segment.

Ensure that the electrical star segment is wired carefully. Keep it as small as possible to avoid interference injection into the electrical star segment, and from here into the entire network. This can be achieved by laying out the OLMs in the electrical star segment directly next to each other on a hat rail.

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