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RS422-RS485

Page history last edited by wilbo666 8 years, 2 months ago


 

Introduction

This page provides information in regards to the RS422 and RS485 standards.

 

RS422 & RS485 Logic Levels

Logic 1 = (Non-inverting - Inverting) > 200mV

Logic 0 = (Non-inverting - Inverting) < 200mV

 

Image taken from http://en.wikipedia.org/wiki/RS-485

 

RS422 & RS485 Idle State

The idle state of RS422 & RS485 is logic 1.

 

Example of External Pull Up Resistors to Achieve Idle State

Image taken from http://www.maxim-ic.com/app-notes/index.mvp/id/1833

 

RS422 & RS485 Serial Port Pinouts

There are no standards for connector pinouts for RS422 or RS485.

 

RS422 & RS485 Signal Specifications

 

RS-485 and RS-422 Standards    
Standard RS-422 RS-485
Mode of operation Differential Unidirectional, Multipoint Differential Full Duplex, Multipoint
Allowed no. of Tx and Rx 1 Tx, 10 Rx 32 Tx, 32 Rx
Maximum cable length 4000ft length 4000ft length
Maximum data rate 10Mbps 10Mbps
Minimum driver output range ±2V ±1.5V
Maximum driver output range ±5V ±5V
Maximum driver short-circuit current 150mA 250mA
Tx load impedance 100Ω 54Ω
Rx input sensitivity ±200mV ±200mV
Maximum Rx input resistance 4kΩ 12kΩ
Rx input voltage range ±7V -7V to +12V
Rx logic high >200mV >200mV
Rx logic low <200mV <200mV

Table taken from http://www.maxim-ic.com/app-notes/index.mvp/id/736

 

References:

max485.pdf

http://en.wikipedia.org/wiki/RS-422

http://en.wikipedia.org/wiki/RS-485

http://www.maxim-ic.com/app-notes/index.mvp/id/736

http://www.maxim-ic.com/app-notes/index.mvp/id/1833

 

Views:

RS-485 and RS-422 Standards  
 
RS-422 RS-485
Mode of operation Differential Unidirectional Differential Full Duplex
Multipoint Multipoint
Allowed no. of Tx and Rx 1 Tx, 10 Rx 32 Tx, 32 Rx
Maximum cable length 4000ft length 4000ft length
Maximum data rate 10Mbps 10Mbps
Minimum driver output range ±2V ±1.5V
Maximum driver output range ±5V ±5V
Maximum driver short-circuit current 150mA 250mA
Tx load impedance 100Ω 54Ω
Rx input sensitivity ±200mV ±200mV
Maximum Rx input resistance 4kΩ 12kΩ
Rx input voltage range ±7V -7V to +12V
Rx logic high >200mV >200mV
Rx logic low <200mV <200mV

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