Priority encoder behavior – if multiple inputs are asserted simultaneously, what does a priority encoder do to resolve the conflict in its encoded output?

Introduction / Context: Standard encoders assume only one input is high at a time. Real systems, however, may present multiple active inputs. Priority encoders are designed to handle such conflicts deterministically by assigning precedence to higher-order inputs, guaranteeing a valid output code and a predictable arbitration outcome.

Given Data / Assumptions:

• Inputs: multiple lines, any of which may be asserted concurrently.
• Priority scheme: higher-numbered (more significant) input has precedence.
• Outputs: encoded binary index and usually a “valid” indicator.

Concept / Approach: A priority encoder scans inputs according to a predefined order and encodes the index of the highest-priority asserted input. In practice, this means lower-priority (less significant) inputs are ignored if a higher-priority line is active. This behavior ensures stable operation in interrupt controllers, bus arbiters, and keyboard encoders where multiple events may coincide.

Step-by-Step Solution:

Verification / Alternative check: Truth tables for 74xx148-type devices show that when multiple inputs are low (active for active-low inputs), the output corresponds to the highest-priority one and the rest are masked, confirming the ignore behavior for lesser inputs.

Why Other Options Are Wrong: Entering fault mode would defeat the purpose of priority handling. “Resampling” does not resolve simultaneous assertion. “Finds some other input” is undefined and non-deterministic. Asserting all outputs simultaneously is nonsensical for an encoder.

Common Pitfalls: Forgetting active-low conventions (many priority encoders use active-low inputs/outputs). Misunderstanding that “ignoring least significant” really means “honoring the most significant first.”

Final Answer: ignores the least significant input