ABB FMBA-01 Kullanıcı Kılavuzu - Sayfa 8

Kontrol Ünitesi ABB FMBA-01 için çevrimiçi göz atın veya pdf Kullanıcı Kılavuzu indirin. ABB FMBA-01 16 sayfaları. Modbus adapter module

Overview

This chapter contains a short description of the RS-485 standard

and the FMBA-01 Modbus Adapter module, and a delivery

checklist.

RS-485 is a serial interface standard for communication over a

twisted-pair cable. Because the RS-485 signal transmission is

differential, it provides better protection against noise and longer

transmission distances than the RS-232. RS-485 is a half-duplex

multi-drop network, which means that multiple devices may reside

on line. Only one transmitter may be active at any given time.

The RS-485 standard specifies only the electrical characteristics

of the bus system. The communication protocol and

communication speed depend on the used application. For

example the electrical characteristics of the PROFIBUS and

MODBUS are based on the RS-485 standard.

The RS-485 transmission line consists of two wires, A and B. The

signal transmission is based on the voltage difference between

the wires. Minimum detected voltage difference is 200 mV. The

potential difference between the two wires determines the logic

state bit: when B is at higher voltage than A, the state is defined as

bit 1 (data high) and when A is at higher voltage than B, the state

is defined as bit 0 (data low).

The common mode voltage between RS-485 network devices is

limited to -5...+12 V. Ground wire and cable shield should be

connected to prevent common mode voltage between the network

devices from drifting outside the allowable limits.

Overview