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July 24, 2008
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RS422/485
Application Note
Table of Contents

Table of Contents
1 - Overview
2 - System Configuration
3 - Selecting Cabling
4 - Transient Protection
5 - Software
6 - Selecting Devices
7 - Further Information
Appendix A - EIA Specs
Appendix B - RS423 Standard

 
Home > Technical Library > RS422/485 Application Note

RS422/485 Application Note
Appendix A: EIA Specification Summary

EIA RS-422 Specification Summary
Parameter Conditions Min Max Units
Driver Output Voltage
Open Circuit		  
 		  
 		 10
-10		 V
V
Driver Output Voltage
Loaded		 RT = 100 Ohms
 		 2
-2		   V
V
Driver Output Resistance A to B   100 OHM
Driver Output Short-Circuit Current Per output to common   ±150 mA
Driver Output Rise Time RT = 100 Ohms   10 % of Bit Width
Driver Common Mode
Voltage		 RT = 100 Ohms   ±3 V
Receiver Sensitivity Vcm <= ±7   ±200 mV
Receiver Common-Mode
Voltage		   -7 +7 V
Receiver Input Resistance   4000   Ohm
Differential Receiver
Voltage		 Operational:
Withstand:		   ±10
±12		 V
V

 

EIA RS-485 Specification Summary
Parameter Conditions Min Max Units
Driver Output Voltage
Open Circuit		  
 		  1.5
-1.5		  6
-6		 V
V
Driver Output Voltage
Loaded		 RLOAD = 54 Ohms
 		  1.5
-1.5		  5
-5		 V
V
Driver Output Short-Circuit Current Per output to +12V or -7V   ±250 mA
Driver Output Rise Time RLOAD = 54 Ohms
CLOAD = 50 pF		   30 % of Bit Width
Driver Common Mode
Voltage		 RLOAD = 54 Ohms -1 3 V
Receiver Sensitivity -7 <= Vcm <= +12   ±200 mV
Receiver Common-Mode
Voltage		   -7 +12 V
Receiver Input Resistance   12K   Ohm

 

EIA RS-232 Specification Summary
Parameter Conditions Min Max Units
Driver Output Voltage Open Circuit  
 		    25 V
Driver Output Voltage Loaded 3 KOhm <=RL<=7 K Ohms 5 15 V
V
Driver Output Resistance, Power Off -2V<=Vo<=2V   300 Ohm
Driver Output Short-Circuit Current     500 mA
Driver Output Slew Rate     30 V/µs
Maximum Load Capacitance     2500 pF
Receiver Input Resistance 3V <= VIN<=25V 3000 7000 Ohm
Receiver Input Threshold
Output = Mark
Output = Space		    
-3
 		  
 
3		  
V
V

 

EIA RS-423 Specification Summary
Parameter Conditions Min Max Units
Driver Output Voltage Open Circuit  
 		  4
-4		  6
-6		 V
V
Driver Output Voltage Loaded RL= 450 Ohms 3.6 6 V
Driver Output Resistance -2V<=Vo<=2V   50 Ohm
Driver Output Short-Circuit Current     ±150 mA
Driver Output Rise and Fall Time Baud Rate <= 1 K Baud
Baud Rate >= 1 K Baud		   300
30		 µs
% Unit Interval
Receiver Sensitivity Vcm <= ±7V   ±200 mV
Receiver Input Resistance   4000   Ohm

 

 

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