On Mon, May 18, 2009 at 5:55 PM, Bob Blick <bobblick@ftml.net> wrote:
> It depends how you drive the bus. With RS-485, when you enable the
> transmitter, both levels (1 and 0) are actively driven onto the bus. So
> it's basically impossible for a local receiver to detect if a remote
> transmitter is colliding. But in buses where one of the levels is
> passively driven(with a resistor), the local receiver can read the bus
> accurately at all times. The disadvantage to this system is the bus can
> only be made as fast as the passive transistion time.
>
> There are more nuances to it, but that's the basic idea behind what
> people have said. There are also busses that have the best of both
> worlds.

Thank you. I get it now.
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