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Pull-up Resistor

What is a pull-up resistor?

A pull-up resistor is a resistor connected between a digital input pin and a positive voltage supply (typically VCC or 3.3V/5V) to establish a default HIGH logic state. It ensures that when a switch or button is not pressed, the input pin reads a stable HIGH voltage instead of floating in an undefined state. Pull-up resistors are commonly used with switches, buttons, and open-drain outputs to prevent erratic behavior from electrical noise and provide reliable digital signal levels.

Related Terms

Pull-down Resistor

A pull-down resistor is a resistor connected between a digital input pin and ground (0V) to ensure the pin reads a logic LOW state when no other signal is present. It prevents the input from floating at an undefined voltage level by providing a path to ground, typically using values between 1kΩ to 10kΩ. Pull-down resistors are commonly used with switches, buttons, and open-collector outputs to establish a known default state and prevent false triggering from electrical noise.