Siemens SIMATIC NET PROFIBUS User Manual

4-49

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

Figure 4-27

RS-485 Bus Terminal

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:

S

6 modular terminals for conductors with a cross-sectional area 

≤

 1.5 mm

2

 for

connection of the incoming and outgoing LAN cable and, if necessary, the
protective earth (PE)

S

Screw down clamps for shield contact

S

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

S

A 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.

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.