Firstly thanks to everyone for their input. I am trying to interface a PIR sensor with the 8051. I thought that maybe I should use the analog I/O ports to do this but none of you guys have mentioned that at all so maybe it is not such a good idea. The sensor uses some sort of photo cell or photo transistor to detect the motion.

I want to set the sensor to be active using the 8051 when a certain condition is true.

Mark Moran