RS485 signal lines

In my research I have found that there is a transmit +, transmit -, receive +, and receive -.

I have read that a -200mV differential results in logic 1 and +200mV differential results in logic 0.

I have read that when line A goes low, B goes high which results in logic 0. When line A goes high and B goes low, results in logic 1.

Are lines “A” and “B” representative of transmit + and - ?

What exactly causes a negative differential and a positive differential?

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