When you unplug the serial console (or keyboard) you're doing the

plug *in*

   equivalent of sending a break to the console which is set up to drop you
   either to the PROM or the debugger.  That's the way SunOS works, that's
   the way Solaris works, and that's the way NetBSD works.  


pulling the kbd out doesn't do much.  it's when you put it back in
that the "break" is generated.


.mrg.