Meaning of CLEAR/RESET in flip-flops: By definition, asserting CLEAR or RESET drives the primary output Q to logic 0. Evaluate the statement: “The Q output of a flip-flop is normally HIGH when the device is in the CLEAR or RESET state.”
Correct Answer: Incorrect
Introduction / Context:Asynchronous control inputs on flip-flops are labeled PRE (preset) and CLR (clear) or SET and RESET depending on convention. Their purpose is to force the output to a known state for initialization or control.
Given Data / Assumptions:
- CLR/RESET forces Q = 0 by definition.
- PRE/SET forces Q = 1 by definition.
- Active levels (low or high) depend on device family but the logical effect is consistent.
Concept / Approach:If a device is said to be in “CLEAR” or “RESET,” its Q output is driven to 0. Therefore, the statement claiming Q is HIGH during CLEAR/RESET is backwards. Only PRE/SET produces Q = 1. Confusion often arises from active-low pin naming (e.g., CLR̄), but the functional outcome at Q is unambiguous.
Step-by-Step Solution:
Map control names to outcomes: CLEAR/RESET → Q = 0; PRE/SET → Q = 1.Check device truth table for active-low vs active-high pins.Verify that the effect on Q does not depend on edge polarity of the clock.Conclude the statement is incorrect.Verification / Alternative check:Consult typical 7474 or 74HC74 tables: CLR̄ asserted low drives Q = 0 immediately, proving the point.
Why Other Options Are Wrong:
- Correct: Opposite of defined behavior.
- NAND-based / negative-edge / supply ramp rate: Implementation details and clocking do not invert the meaning of CLEAR/RESET.
Common Pitfalls:Mixing up active-low pin assertions; confusing PRE/SET with CLR/RESET; assuming clock is required for asynchronous actions (it is not).
Final Answer:Incorrect