I am interpreting this as a 5 unit multi-drop network.
One unit will be master and the other three will be slaves.
One simple approach would be to select 5V as the marking ( idling  
condition )
and zero volts as the space ( start ) condition.
All of the units shall tri-state their output or the output can be  
open-collector.
In either case you will want a pull-up resistor to 5 V.
The master queries one of the 4 slaves and then waits for an answer.
The master can send a break condition to reset the network.

The devil is in the details, however.  this answer will provoke more  
questions than
it answers.  Victor, your response will determine what the details  
will be.

Gus



On 2006-Apr 22, at 7:27 PM, Vic Fraenckel wrote:

I need to multiplex one RS232 serial port to one of four RS232 ports.  
Can this be done? Can a TTL Serial port be multiplexed to 4 TTL  
Serial ports? Some TTL devices require inverted signals and some do  
not. How would I handle this? Standard Baud rates to a minimum of  
9600. Computer control of port selection.

I want to build this my self not purchase an off-the-shelf solution.

Any enlightenment will be appreciated.

Vic
________________________________________________________

Victor Fraenckel - The Windman
victorf ATSIGN windreader DOT com
KC2GUI

       Home of the WindReader Electronic Theodolite
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"Dost thou not know, my son, with how little wisdom the world is  
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