Consider a full-adder with the following input values : (a) π‘₯ = 1,𝑦 = 0 and…

2015

Consider a full-adder with the following input values :

(a) π‘₯ = 1,𝑦 = 0Β and 𝐢𝑖(carry input) = 0

(b) π‘₯Β  = 0,𝑦 = 1Β and 𝐢𝑖 = 1

Compute the value of S(sum) andΒ πΆπ‘œΒ (carry output) for the above input values :

  1. A.

    𝑆=1,πΆπ‘œ=0Β and 𝑆=0,πΆπ‘œ=1

  2. B.

    𝑆=0,πΆπ‘œ=0Β and 𝑆=1,πΆπ‘œ=1

  3. C.

    𝑆=1,πΆπ‘œ=1Β and 𝑆=0,πΆπ‘œ=0

  4. D.

    𝑆=0,πΆπ‘œ=1Β and 𝑆=1,πΆπ‘œ=0

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Correct answer: A

Solution:

Formulas: S = x XOR y XOR Ci. Carry out Co = (x & y) OR (y & Ci) OR (x & Ci).

  • For x = 1, y = 0, Ci = 0: S = 1 XOR 0 XOR 0 = 1. Co = (1&0) | (0&0) | (1&0) = 0. Final: S = 1, Co = 0.

  • For x = 0, y = 1, Ci = 1: S = 0 XOR 1 XOR 1 = 0. Co = (0&1) | (1&1) | (0&1) = 1. Final: S = 0, Co = 1.

Therefore the correct results are: first input set β†’ S = 1, Co = 0; second input set β†’ S = 0, Co = 1.

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