You can do it if you have hardware handshake on all cables. Have a PIC
monitor RTS on each wire and give CTS to one box at a time, also control a
four way switch. The PIC need not 'see' the data but it needs to account
for any latency in the RTS/CTS handshake in the controllers (i.e. how many
characters go out after CTS is turned off). The TxD line from the PC can
be wired directly to all the boxes, through a buffer,  or through a switch
also. For full handshake you also need to switch DTR/DSR. It all depends
on what you are doing and how fast the data is. In any case I'd switch all
the controllers to the highest data rate to buy time for switching gaps
(at least one character).

Peter

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