I plan to use these circuits in my disco lights. Im using 3 pin DMX cables but the last light could be a total of 30-40 meters of wire away from the PC.

Im using the serial RX/TX pins on the pic chip. Last time i tried that i was told its impossible without a MAX232 chip. When in slave mode the chips wont be using serin. It will use the other code which i cant remember off the top of my head but it reads bytes straight from the buffer.

As far as i know i would need a 3rd pin for one of them to act as a master. When acting as a master a normal serout should work fine but its how to connect that pin into the DataIn wire so all theo ther lights pick it up