Recommendation is if you just want a star configuration RS232 that will
work reliably at long distance use RS422 (5-Wires, Full Duplex)
This is same interface used on Macintosh serial ports.  RS485 is an
improvement on RS422 that allows multimaster, which you don't need in a
star configuration.

For RS422 you can basically just use CAT5 Cable, and terminate both ends
with 100ohm resistors, see the national semiconductor application notes.


On Fri, 28 May 1999, John Esposito wrote:

> Hello all:
>
> For the next phase of my PIC project (home security), I want to have remote
> keypads communicating (only) with the master control unit.  I originally
> wanted to use RS232, but was under the impression that RS232 is difficult
> to deal with when using long runs (i.e. through a house) and multiple
> interface nodes.  For future expandability of the "network", I am leaning
> toward RS485, using a Maxim interface chip.  However, I will not run it as
> a multi-drop configuration, but as a star-type configuration, with the
> keypads running (throughout the house) directly to the master.
>
> My question is:  is my impression of RS232 unfounded?  If so, why?  Has
> anyone used RS485 in the way I want to use it?  If so, did you use a
> terminating resistor as each node to minimize reflections?  Any other
> information you could provide would be very helpful
>
>
> Regards,
>
> --John
>