Differences between RS 232 , RS422 , RS485

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Differences between RS 232 , RS422 , RS485

For understanding the difference between RS332 , RS422 and RS485 it is essential to understand 

Single ended Transmission or Balanced 
Differential Transmission or Unbalanced
speed.For more advanced interfaces single return path for each signal in line twisted pair 
cable is required
Advantages of single ended transmission are
Low system cost 
Simple to Implement
Noise and crosstalk
Ground shifts
Low data rates
Low line length
Low sensitivity to crosstalk
Ground Noise rejection
Common mode noise rejection
High signalling rates
Long length upto 1200m
Twisted pair cable is required 
Higher cost
Point to Point - consist of one driver and one reciever
Multi Drop - One driver with Multiple reciever
Multi Point - Multiple drivers and Multiple Recievers
Different bus topology Single Drop and Multi drop


Single Ended Point to Point Bus toplogy

At Driver End
Logic 0 - 5v to 15v
Logic 1 - 5v to -15v
Logic 0 +3 to 15v
Logic 1 -3 to -15v
It allows to connect upto 10 receivers to a driver
Up to 32 devices can be connected


Single ended transmission
Single ended transmission is performed on One signal line and its output and throughput with respect to ground.One common ground is sufficient if the interface is simple and low 
Disadvantages of Single ended transmission
Differential tranmission
For differential transmission a pair conductor is necessary for each channel.One line transmit the true signal while the second line transmit the inverted or false signal transmitted. Ground return line is required to have an interconnection on driver and receiver.
Advantages
Disadvantages
Different Bus topolgy 
RS 232 Transmission is
At Reciever End
Voltages between -3 to 3 is undefined and it is transition region
RS 422 Transmission is
Differential Multi drop interface.
RS 485 is
Differential Multi Point interface

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