ABB FSCA-01, Руководство пользователя

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Overview of the RS-485 network and the FSCA-01 module 19
3
Overview of the RS-485
network and the FSCA-01
module
What this chapter contains
This chapter contains a short description of the RS-485 network
and the FSCA-01 RS-485 adapter module.
RS-485 network
RS-485 (EIA-485, TIA-485) is a balanced (differential) 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 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 application used. For example, the electrical
characteristics of the Modbus protocol are based on the RS-485
standard.