don't care conditions

[Parth86]

don't care condition
C D Q Q0
X X H L
X X L H
X X H H


can anyone explain don't care condition with 0s and 1s number

 

[Ian Rogers]

"Don't care" just means it doesn't affect the output!!

 

[DerStrom8]

Suppose you have a Karnaugh map with some 0s, 1s, and a few "don't cares". Your job is to use the K-map to simplify the expression to the most basic sum-of-products form. When going through the simplification process, for the "don't care" conditions pick the one that allows for the most simplification.

The "don't care" means just that--it doesn't care if it's a 0 or 1, so pick the one that makes things easier to work with and simplify.

Matt

EDIT: I did not see your example at first. The X's in the truth table simply mean that you can ignore them. They have no effect on the outputs Q or Q0

 

[Parth86]

Suppose you have a Karnaugh map with some 0s, 1s, and a few "don't cares". Your job is to use the K-map to simplify the expression to the most basic sum-of-products form.

thanks you are telling about K map to simply the expression
N A B C next state
0 0 0 0 001
1 0 0 0 001
2 0 1 0 011
3 0 1 1 100
4 1 0 0 101
5 1 0 1 110
6 1 1 0 111
7 1 1 1 000
I have simple example for up counter

how to apply k map for this table

 

[DerStrom8]

thanks you are telling about K map to simply the expression
N A B C next state
0 0 0 0 001
1 0 0 0 001
2 0 1 0 011
3 0 1 1 100
4 1 0 0 101
5 1 0 1 110
6 1 1 0 111
7 1 1 1 000
I have simple example for up counter

how to apply k map for this table

Are you familiar with how to set up K-Maps in general? You have 3 inputs, so you will need a 4x2 map (A on the left, BC on the top). It will look something like this (no, the values in the boxes do not symbolize the above question, it's only used to show you how to set it up).

where X1 is A, X2 is B, and X3 is C.

By looking at the truth table you posted, you can place the specified value (1 or 0) into the corresponding boxes of the K-map. From there, simplification happens the same way as any other K-map.

Does this help?
Regards,
Matt