On Fri, 26 Jul 2002 10:14:02 -0700 (PDT) Bill Studenmund
<wrstuden@netbsd.org> sez:

> 2) If you unplug the serial cable regularly (like when it's not in use),
> you probalby want to do a little wiring surgery. Get a resistor, like 47k
> Ohms, and wire it between the receive data input and the DTR pin. When the
> other computer is sending data, this resistor will do nothing (at worst it
> will draw half a milliamp of current). But when the other computer is not
> there, the resistor will keep the receve data pin at the voltage level for
> a '1' bit. Then you won't see a spurrious BREAK sequence.
> 
> Take care,
> 
> Bill

A nifty idea, but RxD to DTR?

Sorry to nitpick, but IIRC, the RS-232 transmit line (or receive --
all point of view), is normally held to low (i.e. < -3.0 Volts, or,
these days, nominally at GND), while DTR asserted will be at > +3.0
Volts.  With your setup, when disconnected, his receive would see a
_constant_ break condition -- as long as DTR were and continued to be
asserted.

If DTR were negated, of course, it would work perfectly well.
Possibly some tty's do that as a matter of course, particularly in
local mode.

Perhaps a better idea would be to use GND instead of DTR?

-Mike