A pull-up resistor is used to keep a digital input in a known high state when the input is floating. Which option best completes?

A pull-up resistor is used to keep a digital input in a known high state when the input is floating. Which option best completes?

• A. Known low state
• B. Unknown state
• C. Known high state
• D. Oscillating state

Answer: (C)

The key idea is biasing an un driven (floating) input so it has a defined logic level. A pull-up resistor ties the input to the supply voltage, creating a weak connection to high. When nothing else drives the line, the input voltage rises to Vcc and the digital input reads as a known high state. If another device actively pulls the line low, it will override the weak pull-up, but with no drive, the input will be high. That’s why the completion is a known high state. The other possibilities would require a different bias (like a pull-down for a known low) or situation where no bias leaves the input unpredictable or could cause oscillation.

The key idea is biasing an un driven (floating) input so it has a defined logic level. A pull-up resistor ties the input to the supply voltage, creating a weak connection to high. When nothing else drives the line, the input voltage rises to Vcc and the digital input reads as a known high state. If another device actively pulls the line low, it will override the weak pull-up, but with no drive, the input will be high. That’s why the completion is a known high state. The other possibilities would require a different bias (like a pull-down for a known low) or situation where no bias leaves the input unpredictable or could cause oscillation.