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Digital Interfaces MCQs

Practice Digital Interfaces MCQs with four options, answers and explanations for focused Electronics & Telecommunication Engineering revision.

Question 1
Digital ElectronicsDigital Interfaces

Which property distinguishes a Schmitt-trigger digital input from an ordinary single-threshold input?

  • AIt has two switching thresholds and hysteresis
  • BIt stores one bit indefinitely
  • CIt always inverts the signal twice
  • DIt requires no supply voltage
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Correct Answer: A. It has two switching thresholds and hysteresis
Explanation: A Schmitt-trigger input uses different rising and falling switching thresholds, creating hysteresis that improves immunity to slowly varying or noisy inputs.
Reference: Standard digital electronics: Schmitt trigger
Question 3
Digital ElectronicsDigital Interfaces

Why are tri-state buffers commonly used on a shared digital bus?

  • ATo allow multiple devices to be connected while only one enabled driver controls the bus at a time
  • BTo make every device drive the bus simultaneously
  • CTo convert the bus to analog
  • DTo eliminate the need for logic levels
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Correct Answer: A. To allow multiple devices to be connected while only one enabled driver controls the bus at a time
Explanation: Disabled tri-state outputs present high impedance, allowing several devices to share conductors while preventing normal operation from having multiple active drivers at once.
Reference: Standard digital electronics: bus interfacing
Question 4
Digital ElectronicsDigital Interfaces

If two push-pull digital outputs connected to the same bus are simultaneously enabled, one driving HIGH and the other LOW, the condition is called?

  • ABus contention
  • BGray transition
  • CClock skew
  • DDynamic refresh
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Correct Answer: A. Bus contention
Explanation: Opposing active drivers on the same line create bus contention, potentially causing excessive current and an undefined bus voltage.
Reference: Standard digital electronics: bus contention
Question 5
Digital ElectronicsDigital Interfaces

An open-collector logic output requires an external pull-up resistor mainly because the output stage can actively?

  • APull the line LOW but does not actively drive it HIGH
  • BDrive only HIGH and never LOW
  • CGenerate an analog sine wave
  • DStore a logic word
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Correct Answer: A. Pull the line LOW but does not actively drive it HIGH
Explanation: An open-collector output provides a transistor path to LOW when active. When inactive, the external pull-up resistor establishes the HIGH level.
Reference: Standard digital electronics: open-collector outputs
Question 6
Digital ElectronicsDigital Interfaces

Multiple compatible open-collector outputs may share a properly pulled-up line to realize which useful connection, provided the logic convention is accounted for?

  • AWired logic
  • BAn analog integrator
  • CA flash ADC
  • DA ring oscillator only
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Correct Answer: A. Wired logic
Explanation: Because any active open-collector transistor can pull the common node LOW while inactive outputs release it, compatible outputs can share a pull-up line to implement wired logic.
Reference: Standard digital electronics: wired logic