Hi Bart,

When you put power to the pic it starts with all it's pins configured as inputs. Nothing you can do about that, just the way things are. They will remain inputs until you tell them to be outputs. During this time the inputs "float", meaning they could be anything between 0 and 5 volts. If the device you're controlling with such a pin is sensitive enough it could get triggered by this floating signal. A simple way to prevent this from happening is to connect a resistor between the pin and Vcc, this is called a pullup. When the pin is floating(input) this resistor will "pullup" the pin to a high state. If you want the pin to be low on startup you should connect the resistor to GND, now you have a pulldown. When your program sets the pin to output, the resistor isn't needed anymore but it won't do any harm either, exept consume some current(biggers res = less current). Your pullup(down) could be anything between 1k and 1M, it all depends on your application. If the device you're controlling is current(not voltage) controlled, like a LED or bipolar transistor, you don't need a pullup or down. If it's a FET or IC you probably do.

/Ingvar