Arithmetic Circuits
243
Figure 7.14 Truth table of a full subtractor.
1
1
1
1
B in
B in
B in
AB
AB
AB
(a)
AB
AB
1
1
1
1
B in
B in
B in
AB
AB
AB
(b)
AB
AB
Figure 7.15 Karnaugh maps for difference and borrow outputs.
The Karnaugh maps for the two expressions are given in Fig. 7.15(a) for DIFFERENCE output D and
in Fig. 7.15(b) for BORROW output B o . As is clear from the two Karnaugh maps, no simplification
is possible for the difference output D. The simplified expression for B o is given by the equation
B o = AAB + AAB in + BBB in
(7.16)
243
Figure 7.14 Truth table of a full subtractor.
1
1
1
1
B in
B in
B in
AB
AB
AB
(a)
AB
AB
1
1
1
1
B in
B in
B in
AB
AB
AB
(b)
AB
AB
Figure 7.15 Karnaugh maps for difference and borrow outputs.
The Karnaugh maps for the two expressions are given in Fig. 7.15(a) for DIFFERENCE output D and
in Fig. 7.15(b) for BORROW output B o . As is clear from the two Karnaugh maps, no simplification
is possible for the difference output D. The simplified expression for B o is given by the equation
B o = AAB + AAB in + BBB in
(7.16)