What is a pull-up or pull-down resistor and what are they used for? Pull-up resistors are resistors used in logic circuits to ensure a well-defined logical level at a pin under all conditions. They create a logic high. Pull down resistors work similarly; except they create a logic low. Pull up resistors are generally used more often than pull down resistors. A common use of these resistors is interfacing a switch of some sort or another input with a microcontroller/ digital gates. They are also used in analog to digital convertors to provide a controller current flow, and in 12C protocol busses, where pull up resistors are used to enable a pin. Question 2 What happens when a switch/button is connected to a button without a resistor connected to a digital port? I