Synchronous vs. asynchronous logic — classification check: Simple gate networks (pure combinational logic) have no clocked storage and thus are asynchronous; transparent S–R latches are level-sensitive, not edge-synchronous. Evaluate the statement: “Simple gate circuits, combinational logic, and transparent S–R flip-flops are synchronous.”

Difficulty: Easy

Correct Answer: Incorrect

Explanation:


Introduction / Context:
In digital design, “synchronous” implies that state changes happen in lockstep with a timing reference (usually a clock edge). Combinational circuits lack memory and do not synchronize to a clock, and transparent latches follow inputs while enabled rather than at discrete edges.


Given Data / Assumptions:

  • Simple gate circuits: no storage, purely input-driven.
  • Combinational logic: outputs are functions of current inputs only.
  • Transparent S–R latch: level-sensitive; follows inputs during enable.


Concept / Approach:
Because combinational logic has no concept of “state update on a clock,” it is asynchronous. Transparent latches change state whenever the enable is active (level), not strictly at a clock edge. Hence calling all of these “synchronous” is incorrect in the conventional clocked-systems sense.


Step-by-Step Solution:

Classify combinational networks as asynchronous (no clocked memory).Classify transparent latches as level-controlled, not edge-synchronous.Reserve “synchronous” primarily for edge-triggered flip-flop systems or level-gated systems treated as synchronous only within controlled intervals.Therefore, the global statement is false.


Verification / Alternative check:
Timing analysis: combinational propagation delays exist without reference to a clock; latches require careful enable timing to avoid transparency hazards, reinforcing they are not purely edge-synchronous.


Why Other Options Are Wrong:

  • Correct: Contradicted by definitions.
  • “Only synchronous when gated by RC” or “fan-in limited to 2” or “Schmitt-trigger gates”: These conditions do not change the fundamental classification.


Common Pitfalls:
Equating “has timing” with “is synchronous”; ignoring the difference between level gating and edge triggering; overlooking that combinational logic has no internal state to synchronize.


Final Answer:
Incorrect

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