Re: RS485 is bidirectional does it mean it is fullduplex?

May I summary this ?

I think RS485 problem is 2 :
*) Noise over long distance cable and
*) Faulty data because of different node voltage reference

To prevent noise over long distance cable, we can earth one side of the
cable shield (refer to Ott, Henry, Noise Reduction Techiques in
Electronic Systems).

To prevent faulty data because of different node voltage, we can use
common line. But since RS485 is a differential mode protocol, we can
use either A or B line as our common line.

However, if we connect using this fashion, when the master is in the
idle mode, there will be floating voltage between A or B line (since
nobody is driving the bus). Therefore, we connect pull-up/pull-down
resistors in the A and B line (to give at least definite voltage level
when nobody's driving the bus).

To make this "definite voltage level" same at the receiver /
transceiver point, we need to earth their voltage reference node at the
both side.

I think everyone is correct here. Just the naming convention that makes
confusion.

Peace everyone =p

-kunil

.

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