Combinational vs. sequential logic — key difference Which statement best captures the difference between combinational logic and sequential logic in digital systems?

Introduction / Context:
Digital subsystems are broadly divided into combinational logic and sequential logic. Combinational circuits compute outputs purely from present inputs, while sequential circuits store state and usually change outputs in response to clock (timing) events. Distinguishing these categories is foundational for timing analysis, hazard mitigation, and state-machine design.

Given Data / Assumptions:

• Combinational logic: no memory, outputs = f(current inputs).
• Sequential logic: has memory (flip-flops/latches), typically clocked.
• Positive logic conventions and idealized devices assumed.

Concept / Approach:

Because sequential circuits store prior information, they need an event to update state. In synchronous systems this is a clock edge; in asynchronous sequential designs, internal conditions cause transitions, but practical mainstream designs are clocked. Combinational logic does not require a clock; it reacts immediately (after propagation delay) to changes at its inputs.

Step-by-Step Solution:

Verification / Alternative check:

Truth tables suffice for combinational blocks; sequential blocks require state tables/diagrams indicating transitions on clock edges or conditions.

Why Other Options Are Wrong:

“Both triggered by timing pulses” is incorrect; only sequential logic inherently needs timing to update state.

“Neither is triggered” ignores the role of the clock in sequential systems.

Common Pitfalls:

Equating asynchronous sequential circuits with combinational logic; forgetting that even combinational blocks exhibit propagation delay but do not require a clock to function.

Final Answer:

Combinational circuits are not triggered by timing pulses, sequential circuits are triggered by timing pulses.