In a pull-down resistor, the default state for a digital input when the circuit is open is which?

In a pull-down resistor, the default state for a digital input when the circuit is open is which?

• A. To provide wireless charging
• B. To define a default known state for a digital input when the circuit is open or disconnected
• C. To increase the voltage
• D. To reduce noise only

Answer: (B)

A pull-down resistor sets a known low level on a digital input when nothing else is driving the line. An input left open tends to float and can pick up stray voltages, causing unpredictable readings. By connecting the input to ground through a resistor, the default state becomes low whenever the circuit is open or disconnected, ensuring stable and predictable logic levels. This is why the purpose of a pull-down is to define that default low state. The other options don’t fit: wireless charging is irrelevant to input biasing, the resistor doesn’t raise voltage (it merely ties the line toward ground when not driven), and while it helps reduce false triggers from noise, its primary role is establishing the known low state.

A pull-down resistor sets a known low level on a digital input when nothing else is driving the line. An input left open tends to float and can pick up stray voltages, causing unpredictable readings. By connecting the input to ground through a resistor, the default state becomes low whenever the circuit is open or disconnected, ensuring stable and predictable logic levels. This is why the purpose of a pull-down is to define that default low state. The other options don’t fit: wireless charging is irrelevant to input biasing, the resistor doesn’t raise voltage (it merely ties the line toward ground when not driven), and while it helps reduce false triggers from noise, its primary role is establishing the known low state.