Andre,

You can attach multiple RS485 trancievers to the same
RS485 bus.  The trancievers go into a high impedence
state when they are not transmitting.

You probably can get by with RS485 (2 wires) rather
than RS422 (4 wires) unless you really need
full-duplex operation.

See link below for a good reference document on RS485
and RS422:

http://www.bb-elec.com/tech_articles/rs422_485_app_note/table_of_contents.asp

Kirk

> Hi to all,
>
> Soon my electronic gate will be ready witch is
> About 120 feet far from my desk and I need to
> Build bidirectional communication with whole
> House there are doors and switches I need to know
> The status of it. My favorite interface is I2C but
the problem
> Is that I2C is not good for 120 feet distance I
guess my
> Choice is RS485 differential phase but what I do not
know is
> By using 4 wires 2 for receive and 2 for transmit
can I communicate
> with all 35 sensors ?. So rs485 works like rs232 I
do not see any way
> of sharing from same bus I need to make
communication like I2c but
> for 120 feet long any help will highly appreciated.
>
> Andre

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