Combinational versus memory behavior: A “combinational logic circuit” is claimed to have memory that remembers prior inputs after they are removed. Evaluate this statement in the context of digital design.

Introduction / Context: Digital circuits fall broadly into two classes: combinational logic and sequential logic. Knowing which category a circuit belongs to determines how its outputs are interpreted and how it is verified or synthesized in hardware description languages and gate-level implementations.

Given Data / Assumptions:

• Combinational logic: outputs depend only on present inputs (function of current values).
• Sequential logic: outputs depend on present inputs and past history (state), usually via feedback or storage (latches/flip-flops).
• No implicit storage elements are included unless specifically designed.

Concept / Approach: The defining property of a combinational circuit is the absence of memory. Its output can be written as Y = f(X) for current inputs X. If memory were present, we would need state variables S and next-state equations to describe behavior (Y = g(X, S)). Therefore, stating that combinational logic “remembers” past inputs is contrary to definition.

Step-by-Step Solution:

Verification / Alternative check: Truth tables for logic gates (AND, OR, XOR, etc.) and for combinational blocks (adders, encoders, multiplexers) map present inputs directly to outputs; no timing history or clock is needed. In contrast, latches and flip-flops require a clock or feedback path to hold information.

Why Other Options Are Wrong: “Correct” contradicts the standard definition. Hazards or high-impedance outputs do not provide memory in the Boolean sense; they are implementation details or bus states, not logic storage.

Common Pitfalls: Confusing propagation delay or glitching with memory; assuming that because combinational circuits can be embedded in systems with memory, they themselves must remember data.

Final Answer: Incorrect