Don’t Cares

Recall that Don’t Cares are labeled as ‘X’s in truth table. Can treat X’s as either ‘0’s or ‘1’s

Row A B C D F(A,B,C,D)  0 0 0 0 0 0  1 0 0 0 1 0 2 0 0 1 0 1 3 0 0 1 1 1 4 0 1 0 0 0 5 0 1 0 1 0 6 0 1 1 0 1 7 0 1 1 1 0 8 1 0 0 0 0  9 1 0 0 1 010 1 0 1 0 x11 1 0 1 1 x12 1 1 0 0 x13 1 1 0 1 x14 1 1 1 0 x15 1 1 1 1 x

F(ABCD)Recognize BCD numbers: 2,3,6

A

B

C

D

Non BCD numbers are don’t cares because will never be applied as inputs.

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