Question

Consider a 4 bit ripple carry adder with inputs A[3:0]=0101 and B[3:0]=0011. What are the results of full adder for bit 3 ?

O Cout=0, Sum=1
O Cout=1, Sum=1
O Cout =1, Sum =0
O Cout=0, Sum=0
​

Answer 1

For the 4-bit ripple carry adder with inputs A[3:0] = 0101 and B[3:0] = 0011, the results of the full adder for bit 3 are Cout = 0 and Sum = 0, considering no carry from the previous bit.

Step-by-step explanation:

To answer this question, we must perform bit-level addition for the most significant bit (bit 3) of the two 4-bit numbers, considering any carry input from the previous bit (bit 2).

For the inputs, A[3:0] = 0101 and B[3:0] = 0011, we are specifically looking at A[3] = 0 and B[3] = 0, and assuming that the carry input from bit 2 (Cin[2]) is 0 since the partial sums of lower bits (bit 1 and bit 0) are both 1 and won't affect the carry out for bit 3.

Using the full adder formula:

• Sum = A XOR B XOR Cin
• Cout = (A AND B) OR (A AND Cin) OR (B AND Cin)

We get:

Sum[3] = 0 XOR 0 XOR 0 = 0
Cout[3] = (0 AND 0) OR (0 AND 0) OR (0 AND 0) = 0

Therefore, the results for the full adder for bit 3 are:

Cout = 0, Sum = 0