solarwind escreveu:
> 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.
>>     =


But certainly tens of thousands of bps are possible. I use 19.2 kbps
with a "passivated" RS-232 network (every transmitter have a diode in
series with the TX pin and the line is pulled down to -12V with a 3k3
resistor) over 100m long.

I have installed systems with up to six nodes distributed along the line.

I use 19.2 kbps because of system convenience but in tests it worked up
to 57.6kbps.

For RS-485, I think much higher speeds are possible, even with a
passively pulled state.

Regards,

Isaac


>> 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.
>   =


__________________________________________________
Fa=E7a liga=E7=F5es para outros computadores com o novo Yahoo! Messenger =

http://br.beta.messenger.yahoo.com/ =


-- =

http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist