Computer Interfacing
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termination resistor


       Computer Interfacing Forum Index -> RS422 and RS485
Author Message

Apr 14, 2011 11:39 am


please let me know

1> why the value of termination resistor is 120 ohm?

2> if i use termination resistor to the every node instead of 2 sides of the bus then whether it will be correct? if yes then whether the values of each resistor become less of 120 ohm?

with thanks
willam Asansol

Oct 19, 2011 2:25 pm

1. 120 Ohm is the characteristic impedance of Cat5E/Cat6 cable. Their purpose is to prevent unwanted signal reflections or ringing in an unterminated line.

2. Putting termination resistors at each node, instead of at the ends of the cable/bus will quickly compromise the integrity of the bus and while you will get away with it at 2 nodes Smile, then by 20 nodes it will not work correctly, becoming too low resistance.

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