Digital Systems: Principles and Design

89Karnaugh Map and Minimization Procedures

the dont care input states. Use it at places where it leads to simplification and leave it where

it does not lead to simplification. The improved adjacencies lead to simplification of the

circuit design.

We can take x for determining the adjacent pairs or quads or octets. Table 5.17 shows

the use of dont care in selecting conditions the adjacencies. Assume that

A

.B.

C

.

D

and

A

.B.C.D and A.

B

.

C

.D are dont care input states [(A = 0, B = 1, C = 0 and D = 0), A = 0,

B, C and D = 1), and (A = 1, B = 0, C = 0 and D = 1)].

We can use the two dont care conditions to make two octets and leave and ignore third

one