Question

For a binary half-subtractor having two inputs A and B, the correct set of logical expressions for the outputs D =( A minus B) and X =( borrow) are

• A. $D=AB+\overline{A}B,X=\overline{A}B$
• B. $D=\overline{A}B+A\overline{B}+A\overline{B},X=A\overline{B}$
• C. $D=\overline{A}B+A\overline{B},X=\overline{A}B$
• D. $D=AB+\overline{A}\overline{B},X=A\overline{B}$

Answer 1

The correct option is C $D=\overline{A}B+A\overline{B},X=\overline{A}B$

$A$ $B$ D
(difference) X
(borrow)

0	0	0	0
0	1	1	1
1	0	1	0
1	1	0	0

$D=A⨁B=\overline{A}B+A\overline{B}$
$X=\overline{A}B$