Digital design fundamentals A half-adder vs. full-adder: Would you normally use a half-adder whenever a carry input (Cin) is required in an adder circuit?

Introduction / Context:
This question checks understanding of the difference between a half-adder and a full-adder in digital electronics. Adders are fundamental building blocks for arithmetic logic units; knowing when to use each type ensures correct handling of carry propagation in multi-bit addition.

Given Data / Assumptions:

• A half-adder has two inputs: A and B; it outputs Sum and Cout (carry out) but has no carry input.
• A full-adder has three inputs: A, B, and Cin; it outputs Sum and Cout.
• We consider standard binary addition with possible incoming carry from a lower-order stage.

Concept / Approach:
When cascading adders to form multi-bit adders, each bit position except the least significant bit must accept a carry input from the previous position. Therefore, a circuit that requires Cin must be implemented with a full-adder, not a half-adder.

Step-by-Step Solution:
Define requirement: We need an adder stage with a carry input (Cin).Half-adder capability: computes A + B only; there is no terminal for Cin.Full-adder capability: computes A + B + Cin; it explicitly supports cascading.Conclusion: If Cin is required, use a full-adder, not a half-adder.

Verification / Alternative check:
Observe a 4-bit ripple-carry adder schematic: the least significant bit may be a half-adder if Cin = 0, but all higher bits must be full-adders because Cin is needed.

Why Other Options Are Wrong:
True / Depends / Only when Cin = 0 / Only for LSB: A half-adder lacks Cin entirely; only a full-adder supports Cin regardless of bit position.

Common Pitfalls:
Confusing the presence of Cout in a half-adder with the ability to accept Cin. Cout is an output; Cin requires an extra input port that the half-adder does not have.

Final Answer:
False