Digital design fundamentals: A full subtractor circuit requires how many inputs and how many outputs?

Introduction / Context:
Binary subtractors compute difference bits and borrow bits. A full subtractor, like a full adder, accounts for a borrow from the previous less significant stage, making it useful in multi-bit subtraction.

Given Data / Assumptions:

• Inputs typically: A (minuend bit), B (subtrahend bit), and Bin (borrow-in).
• Outputs typically: D (difference) and Bout (borrow-out).
• We assume active-high logic.

Concept / Approach:
Define the function: D = A ⊕ B ⊕ Bin and Bout = (¬A & B) + (Bin & ¬(A ⊕ B)). This formulation shows the need for three inputs and two outputs.

Step-by-Step Solution:
Identify required bits: A, B, and Bin → 3 inputs.Compute outputs: D (difference), Bout (borrow-out) → 2 outputs.Therefore: three inputs and two outputs.

Verification / Alternative check:
Compare to a half subtractor (only A and B, producing D and Bout with no borrow-in) → 2 inputs, 2 outputs. The presence of Bin distinguishes the full subtractor.

Why Other Options Are Wrong:
Two-input answers describe a half subtractor, not full.Three inputs and one output omit either D or Bout, which is incomplete.Four-input option does not match minimal standard full subtractor design.

Common Pitfalls:
Confusing full subtractor with full adder or forgetting the borrow-in, leading to an incorrect input count.

Final Answer:
three inputs and two outputs