Hi again, I finally got around to measuring the voltage that comes out of RTS. It is about 6V when on and -6V when off. That seems to work an LED fine but what about the MAX485 chip? Ive looked at the datasheet and it appears that "low" is classed as below 0.8V and "high" is 2V or more. Is 6V too much for the chip? It doesnt seem to give a max value for that. I would assume the max input voltage is about the same as VCC. Do i need a diode or anything to stop the negative voltage going into the DE and RE pins?