Gantner IDL 101 - Bus Interface

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IDL 101

STRUCTURE OF THE BUS TOPOLOGY

HB_IDL101_E_V222.doc

Gantner Instruments Test & Measurement GmbH

4.1. Bus interface

The bus interface in the sensor modules is an RS485 interface. Its advantages over traditional RS232 connections are a

larger number of users, its greater transmission speed, its greater immunity to interfering and the long line length that

are mostly required.

transmission speed

1 K 10 K 100 K

187,5 K

1 M 10 M

[bps]

10 m (32.5 ft)

100 m (325 ft)

1000 m (3.250 ft)

1200 m (3.900 ft)

transmission

600 m (1.950 ft)

RS 232

RS 422

RS 485

line length

Figure 4.1 Interrelation between transmission speed and line length

4.2. Bus Structure

The bus structure is a line structure where each bus segment will be blanked off with characteristic impedance on both

ends. Branches can be build up over a bi-directional signal amplifier, so called repeater. Other than that branches are

not permitted (no tree topology). The max. stub to a user is not allowed to exceed 30 cm (12 inches).

The following figures show a few examples for a possible set-up of bus topologies. The meaning of the symbols is:

: bus user : repeater : bus termination.

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Figure 4.2 Simple line structure

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Figure 4.3 Extended line structure