Actually, if I'm not mistaken, 485 requires +5V and -5V....its a bi-directional signal. That means that when a "0" is being transmitted, one line is +5V and the other is -5V.....when a 1 is being transmitted, both lines are close to 0V.

As for why you aren't reading a signal, I've got no idea, but I'd agree that the RTS line needs to change state. I seem to think you can handle this manually, and suggest you look at the serial communications documentation.

Paul