public void SetSignal (SerialSignal signal, bool value)
{
if (signal < SerialSignal.Cd || signal > SerialSignal.Rts ||
signal == SerialSignal.Cd ||
signal == SerialSignal.Cts ||
signal == SerialSignal.Dsr)
throw new Exception ("Invalid internal value");
if (set_signal (fd, signal, value) == -1)
ThrowIOException ();
}