Siemens SIMATIC NET PROFIBUS, Owner'S Manual, Page: 449 / 490

Network Topology
4-3
PROFIBUS Optical Bus Terminal (OBT)
C79000-G8976-C122-02
4.3 Attaching RS-485 Segments
The OBT allows the attachment of a single PROFIBUS DP node. To attach
RS-485 segments with more than one node, a further network component is
available, the OLM 12M. The requirement for using the OLM 12M is that the
PROFIBUS DP network is operated at a transmission rate of 187.5 Kbps, 500
Kbps, 1.5 Mbps or 12 Mbps.
The optical channels of the OLM 12M can be connected as follows with the OBT or
with other SIMATIC devices on the optical PROFIBUS DP:
The connection is established with a two-fiber plastic FO cable (maximum length
50 m) or PCF FO cable (maximum length 300 m). The fiber-optic cable has two
simplex connectors at each end. The optical channel of the OLM 12M connected
to the OBT must be operated in the “Line“ mode with the monitoring deactivated.
1) PROFIBUS cable
(terminated at both ends)
2) PROFIBUS cable
3) PROFIBUS connector (not terminated)
4) Plastic FO or PCF FO with two fibers
ET 200M without
FO interface
DP node without
FO interface
SIMATIC S7-400
with IM 467 ET 200M without
FO interface
À
Terminating resistor activted
2)
2)
2)
3)
4)
4)
1)
1)
OBT
OBT
OBT
À
À
À
À
À
À
3)
Figure 4-2 Example of Attaching RS-485 Segments