In electronic logic circuits, a pull-up resistor (PU) or pull-down resistor (PD) is a resistor used to ensure a known state for a signal. It is typically used in combination with components such as switches and transistors, which physically interrupt the connection of subsequent components to ground or to V CC.

A pull-up resistor is used in electronic logic circuits to ensure a known state for a signal. It is usually used in combination with transistors and switches to ensure the voltage between ground and V cc is actively controlled when the switch is open (similar to a pull-down resistor).

The pull-up resistor is paired with a switch to ensure that the voltage between Ground and VCC is actively controlled when the switch is open. At the same time, it will not affect the state of the circuit. If we do not use a pull-up resistor, it will result in a short circuit.

Pull-up and pull-down resistors are components added to circuits to ensure that pins on a microcontroller have a known voltage level, usually either VCC (5V or 3V) or GND (0V), before they are actively driven by other components. Pull-ups pull the voltage level up to VCC when the pin is not active, while pull-downs pull the voltage down to 0V.

Pull-up resistors are simple fixed value resistors, that are connected between the voltage supply and the particular pin. These resistors are used in digital logic circuits to ensure a logic level at a pin, which results in state wherein the input/output voltage is nonexistence driving signal.