> Both SunOS and NetBSD on the sun3 are sensitive to "line break"
> on the tty port when used as the console.  That is how you drop
> into the PROM or kernel debugger.  Unplugging a terminal usually
> will cause a line break.  To prevent this, you could wire up a
> plug with the data line held inactive and keep that in place of
> the terminal.  I think wiring for such a plug has been presented
> in one of the sun newsgroups (i.e. comp.sys.sun.admin).

Alternatively (take this with a large grain of salt, never tried this) you can
wire up a straight-through cable and connect pins 2 and 3 by a 10K resistor at
one end.

With a terminal plugged in, this hack will draw a minimal amount of current.
Unplug your terminal, and the receive line will assume the voltage of the
transmit line, which will be a mark.