K-maps and don't cares

• Don't cares can be treated as 0s or 1s

  • Example: minimize F(A,B,C,D) = ?m(1,3,5,7,9) + d(6,12,13)
    • With and without using don't cares

0 0 X 0

1 1 X 1

1 1 0 0

0 X 0 0

AB

CD

A

B

D

00

01

11

10

00

01

11

10

C

Use X == "1"? allows a 2-cube rather than a 1-cube

0 4 12 8

1 5 13 9

3 7 15 11

2 6 14 10

F = A'D + B'C'D without using don't cares

F = A'D + C'D using don't cares

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