Another 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.