special wiring for RS485?

Einly · Joined: 10 Sep 2003 Posts: 60

Hi, I found a Shimaden temperature controller that only
using 2 wires +, - to connect to a RS485 to RS232
converter and then link to PC for cotrol purpose.

The system can read and write signal to/from the controller.

So, I just dubt why it doesn't use GND line also can work.

Thanks...

Einly,
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Einly

Mark · Joined: 07 Sep 2003 Posts: 2838 Location: Atlanta, GA

RS485 uses differential voltage. That means that it subtracts the voltage between the two lines to get the data. Therefore there is no need for the ground which would be your reference voltage.