Pulse-triggered flip-flops — functional description Which statement best describes the action of a pulse-triggered flip-flop in a synchronous digital system?
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AThe clock and the S–R inputs must be pulse shaped.
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BThe data is entered on the leading edge of the clock, and transferred out on the trailing edge of the clock.
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CA pulse on the clock transfers data from input to output.
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DThe synchronous inputs must be pulsed.
Answer
Correct Answer: A pulse on the clock transfers data from input to output.
Explanation
Introduction / Context:Pulse-triggered flip-flops are designed to respond to a narrow clock pulse rather than a sustained logic level. They bridge the conceptual gap between level-sensitive latches and ideal edge-triggered flip-flops by reducing the effective sampling window to a short interval. Understanding their behavior helps you reason about timing windows, metastability risk, and clock conditioning in real hardware.
Given Data / Assumptions:
- The device expects a brief clock pulse (generated internally or externally).
- Data inputs are considered synchronous and must meet setup/hold relative to the pulse.
- We are describing functional behavior, not specific pin polarities.
Concept / Approach:When a properly timed clock pulse arrives, the flip-flop samples the input and updates the output accordingly. Outside of that short pulse interval, input changes are ignored, thereby preventing level tracking. This emulates edge-triggered behavior sufficiently for many applications, assuming pulse width is controlled to avoid multiple toggles.
Step-by-Step Solution:
1) Recognize that the device is inert until a clock pulse occurs.2) During the pulse, the data path is enabled and the input state is captured.3) After the pulse ends, the output holds the captured value.4) Proper setup/hold timing around the pulse prevents metastability.Verification / Alternative check:Inspect timing diagrams: the output transitions only during the short pulse; making the pulse too wide effectively reintroduces level sensitivity.
Why Other Options Are Wrong:
- Pulsing S–R or synchronous inputs specifically is not required; the clock pulse is the trigger.
- Leading-edge enter and trailing-edge transfer describes master–slave operation, not pulse-triggered directly.
Common Pitfalls:Using excessively long clock pulses that allow unintended multiple transitions; failing to meet setup/hold around the pulse edges.
Final Answer:A pulse on the clock transfers data from input to output.