To give you an idea of why they are weak pull up resitors you have to see the datasheet. According to that, the PORTB weak pull-up current has a maximum of 400uA current available..... now that is weak :lol: The purpose of these pull-ups is to make the pin high in the absence of a signal, so that it doesn't stay floating around. And allows you to reduce the parts you need tooAnother example of potential disaster is that PORTA, pin 4 exhibits unusual behavior when used as an output. This is because the pin has an open drain output rather then the usual bipolar stage of the rest of the output pins. This means it can pull to ground when set to 0, but it will simply float when set to a 1, instead of going high. To make this pin act in the expected manner, add a pull-up resistor between the pin and 5 volts. The value of the resistor may be between 1K and 33K, depending on the drive necessary for the connected input. This pin acts as any other pin when used as an input.