Siemens SIMATIC NET PROFIBUS manual Example of Attaching RS-485 Segments

Network Topology

4.3Attaching 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.

ET 200M without	DP node without	SIMATIC S7-400	ET 200M without
FO interface	FO interface	with IM 467	FO interface

À

2)

3)

2)

À
											À
2)							À			1)
						1)
				OBT
	OBT							OBT
		3)			À
									À
			4)		4)

ÀTerminating resistor activted

1)PROFIBUS cable (terminated at both ends)

2)PROFIBUS cable

3)PROFIBUS connector (not terminated)

4)Plastic FO or PCF FO with two fibers

Figure 4-2 Example of Attaching RS-485 Segments

PROFIBUS Optical Bus Terminal (OBT)	4-3
C79000-G8976-C122-02