So I believe that what I need is either RS-485 or RS-422, though I'm not clear on the difference as one web site intimates that with two of their RS-485 to UART boards I can get the equivalent.In any event I want to have two arduinos be able to communicate back and forth between each other (just two, point to point, no daisy chaining), over a distance of about 60 feet or more, in a somewhat noisy automotive environment. 115kbs is plenty of speed; 9600 might even be fast enough. My aim is mainly to have one arduino act as a monitor and UI (simple 2-line screen, and some buttons) for another arduino that does the real processing and controls a pump. I'll work out a very simple serial protocol. So do I need maybe two of this sort of adapter on each arduino, one for TX and one for RX? http://www.emartee.com/product/42231/RS485%20Module%20%20Make%20Your%20Arduino%20Talk%20With%20Each%20Other Or is there another chip that I can use to get duplex communication (standard UART-style connection on the arduino) over a cat-5 cable? I can certainly wire up my own adapters.