Siemens SIMATIC NET PROFIBUS - Manual (Page 35)

Topologies of SIMATIC NET PROFIBUS Networks
2-9
PROFIBUS Networks SIMATIC NET
6GK1970-5CA20-0AA1 Release 2 05/2000
Star Topologies with OLMs
Several optical link modules are grouped together to form a star coupler via a bus
connection of the RS-485 interfaces. This RS-485 connection allows the
attachment of further DTEs until the maximum permitted number of 32 bus
attachments per segment is reached.
PG
S7-400
OP 25
А
А
А
А Terminating resistor activated
Star hub
А
А
А
1 FO cable
2 LAN cable for PROFIBUS
4 PROFIBUS 830-2 connecting cable
4
2
1
2
2
2
1
À
4
S7-400
À
Figure 2-4 Example of a Star Topology with OLMs
Optical Channels
The OLMs are connected to the star coupler by duplex fiber-optic cables.
Both DTEs and electrical bus segments can be connected to the OLMs attached
by the duplex fiber-optic cables. Depending on the requirements and the distance,
the duplex cables can be implemented with plastic, PCF or glass (OLM only)
fibers.