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

On 2005-06-15, Floyd L. Davidson <floyd@xxxxxxxxxx> wrote:

> RS-485 is a differential (balanced) system, and there is no
> signal ground connection. The cable used might well include a
> frame ground, but that is for noise induction cancellation, not
> signal ground.

In my experience, the third/fifth wire is required to limit the
common mode voltage seen by the receivers. In that respect, it
is a signal ground. IIRC, most receivers them can only tolerate
8-12V common-mode DC. If you let the two devices float with
respect to each other, you can get fairly high common-mode
voltages and the recievers will stop working.

--
Grant Edwards grante Yow! I know how to get the
at hostesses released! Give
visi.com them their own television
series!
.

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