Siemens SIMATIC NET PROFIBUS Design and Functions of the RS-485 Bus Terminal, Bus Terminal RS-485

Passive Components for RS-485 Networks

4.7.2Design and Functions of the RS-485 Bus Terminal

Figure 4-27 RS-485 Bus Terminal

Bus Terminal RS-485

The RS-485 bus terminal is used to connect data terminal equipment (DTEs) with an RS-485 interface to the LAN cable. It includes the following:

S6 modular terminals for conductors with a cross-sectional area ≤ 1.5 mm2 for connection of the incoming and outgoing LAN cable and, if necessary, the protective earth (PE)

SScrew down clamps for shield contact

SA switch (“Bus terminated”) to allow termination at the end of an RS-485 segment with the characteristic impedance

SA connecting cable preassembled (either 1.5 m or 3 m long) with a 9-pin sub-D male connector for direct connection to a DTE.

Cable Termination

The sub-D connector is plugged into the sub-D female connector of the DTE and secured by screws. If the terminating resistor is activated, the RS-485 bus terminal requires current of maximum 5 mA at a power supply of 5 V between pins 5 and 6 of the connector from the DTE.

PROFIBUS Networks SIMATIC NET	4-49
6GK1970-5CA20-0AA1 Release 2 05/2000