Technical data
Topologies of SIMATIC NET PROFIBUS networks
2.2 Topologies of optical networks
PROFIBUS Network Manual
System Manual, Edition 04/2009, C79000-G8976-C124-03
31
Star topologies with OLMs
Several optical link modules are grouped together to form a star coupler via a bus
connection of the RS485 interfaces. This RS485 connection allows the attachment of further
end devices until the maximum permitted number of 32 bus attachments per segment is
reached.
Star point
2
1
1
2
2
2
3
3
1
OP 25
PG
S7-400
S7-400
① Terminating resistor activated
1 Fiber-optic cables
2 PROFIBUS bus cable
3 PROFIBUS connecting cable 830-2
Figure 2-4 Example of a star topology with OLMs
Optical channels
The OLMs are connected to the star coupler by duplex fiberoptic cables.
Both end devices and electrical bus segments can be connected to the OLMs attached by
the duplex fiberoptic cables. Depending on the requirements and the distance, the duplex
cables can be implemented with plastic, PCF or glass (OLM only) fibers.
Monitoring FO links
Using the echo function, the connected OLMs can monitor the fiberoptic sections. A break on
a link is indicated by a display LED and by the signaling contact responding.
Even if only one transmission direction is lost, the segmentation triggered by the monitoring
function leads to safe disconnection of the OLM from the star coupler. The remaining
network can continue to work without problems.