The 'driver' is a PIC output pin with a small series resistor and diode and
a relatively
large resistor from the line to ground.
Definitely not reliable under all circumstances, but enough to daisy chain
a few programmers on my desktop with roughly zero components.
schematics etc: www.xs4all.nl/~wf/wouter/pic/wisp
Wouter.

----------
> From: Gerhard Fiedler <lists@HOME.COM>
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: RS232 Bus
> Date: Thursday, March 25, 1999 09:35
>
> At 07:58 03/25/99 +0100, w. v. ooijen / f. hanneman wrote:
> >For WISP I use rs232 as a 3-wire multi-drop bus (master sends on one,
all
> >slaves send on the other).
> >The addressing is based on using the break condition as atention signal.
>
> what kind of driver do you use for the slave transmitter? rs232 with
active
> low and active high?
>
> ge