> >
> > is it possible that unplugged cable "receives" noise?
> >
> > will just connecting extra resistor between ground and receive fix it?
> >
> > any idea what resisitor? 22KOhm?
>
> 22k Ohm would probably be fine, but I think it'd be better to tie the
> signal to DTR rather than to ground. RS232 signals are defined as being
> 'Mark' (logical 1) if the voltage is between -3V and -25V (I think 25 is
> the right number) and "Space" (logical 0) if between 3V and 25V. Most
> systems use +/-5V or +/-12V.
>

i already "fixed" this by using 38400 instead of 115200.