Logic circuits

In a 1-bit half adder, which logic produces the sum (S) and carry (C)?

  1. ASum is AND, carry is OR
  2. BSum is NOR, carry is NAND
  3. CSum is XOR, carry is AND
Show answer and explanation

Answer: C. Sum is XOR, carry is AND

Adding two 1-bit inputs A and B gives a sum of A XOR B and a carry of A AND B. For example, 1 + 1 is 10 in binary, so the sum is 0 and the carry is 1. A circuit that also adds a carry from the lower digit is a full adder, which can be built from two half adders and an OR gate.

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