Question

. Determine the sum (c) and the output carry (Cout) of a half-adder when the input bits are 1 and 1. b. A full-adder has Cin = 1. What are the sum (c) and the output carry (Cout) when A = 1 and B = 1? c. With the aid of diagram, what are the sum outputs when 111 and 101 are added by the 3-bit parallel adder?

Answer 1

1) Half adder

$A=B=1$ A B Sum Carry

Sum= 0 0 0 0 0

carry=1 0 1 1 0

1 0 1 0

1 1 0 1

2)Full adder

$A=B=C_{in}=1$ A B C Sum Carry

sum=1 0 0 0 0 0

carry=1 0 0 1 1 0

0 1 0 1 0

0 1 1 0 1

1 0 0 1 0

1 0 1 0 1

1 1 0 0 1

1 1 1 1 1

3) Given circuit is parallel adder

Results for FA1

$A=1, B=1, C_{in}=0$

$\sum_1=0$

$C_{out}=1$

Results for FA2

$A=0,B=1,C_{in2}=1$

$\sum_2=0$

$C_{out2}=1$

Results for FA3

$A=1,B=0,C_{in3}=1$

$\sum_3=0$

$C_{out3}=\sum_n=1$

4) Comparator

$A_3,A_2,A_1,A_0$ $B_3,B_2,B_1,B_0$

$0, \space 1,1,0$ $0,1,1,1$