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[moved] differential signalling in RS 485

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vinoth14

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What is meant by differential signalling in RS 485?
 

Re: differential signalling in RS 485

That means that differencial pair is used, like in USB, Ethernet, CAN and e.t.c, but most simplest example.
 

Re: differential signalling in RS 485

Hi,

from the driver side:
If one output goes high, at the same time the other output goes low.
Allways one driver is high, and one driver is low. (as long as you don´t disable the drivers)

at the receiver side:
the logical state is made with a comparator (with hysteresis) that compares both signals.
So if the non_inverting is larger than the inverting input, then the output is high. Independent if the one is at 1V and the other is at 2V, or the one is at 5V and the other is at 4V.

Klaus
 

Re: differential signalling in RS 485

Hi,
You will have a resistor at the receiver side connected between data+ and data- this will result in a current to flow (a few mA)
Compared to single ended signals like RS232 where you only detects the voltage swing.
The RS485 + RS422 will draw a current and thereby the signal will be very immune for noise.

You can use long cable like 1000m also you have twisted pairs of the Data+ and Data- which will reduce external noise like on a balanced microphone cable.
 

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