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

"Floyd L. Davidson" <floyd@xxxxxxxxxx> wrote in message
news:873brik81n.fld@xxxxxxxxxxxxx
> Every telephone cable in the country has the shield connected
> to ground at both ends.

I can assure you that the screen of my telephone cable is NOT connected to
ground on my side.
Which is logical too, because you want to keep any current through the
screen as low as possible and that can onlybe achieved by connecting the
screen at only one side.

> And absolutely unnecessary too. RS-422 works on two pairs. The
> master transmitter and all slave receivers are on one, and the
> master receiver and all slave transmitters are on the other.

And all those slave transmitters should be disabled, except the one that's
talking to the master.

> They are *all* high impedance devices, relatively. There has to
> be a 100 Ohm load resistor on each pair.
>
> >hard. However, both RS-232 and RS-422 can be used in a multidrop
> >configuration with a few diodes, but this would reduce the noise
> >margins, since the bus would only be actively driven into the Space
> >state, while passively pulled by bias resistors to the Mark (which
> >also is the idle state).
>
> Unnecessary for RS-422.

So, if all slaves have a dominant Mark, how is one slave going to drive a
Space on the line?

Meindert


.

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