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Member since:
June 06, 2007
Total points:
491 (Level 2)

## Resolved Question

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# Difference between positive and negative logic?

I am taking a digital logic class and we need to know how to use negative logic but they haven't done a very good job of teaching this so I am a little confused.

For example, given the following truth table (where F is output):
A | B | C | F |
-----------------
L | L | L | L |
L | L | H | L |
L | H | L | H |
L | H | H | H |
H | L | L | L |
H | L | H | L |
H | H | L | H |
H | H | H | H |

Describe the circuit in (a) positive logic and (b) negative logic.

I know for positive logic you would replace the Hs with 1s and Ls with 0s. Then F(A,B,C) would equal all terms (each term would be made up the variables equal to 1 in that row ANDed with the variables equal to 0 set to their NOT) corresponding to rows with output of 1 ORed together.

Now with negative logic I know the Hs would be replaced with 0s and the Ls would be replaced with 1s. I'm not sure how to proceed after this point.

I would like a detailed view of how to represent using negative logic.

6 years ago

by Warren W
Member since:
October 12, 2007
Total points:
362 (Level 2)

## Best Answer - Chosen by Asker

Negative logic is just like positive logic, only the desired output is a logic 0 instead of a logic 1. For example, an AND gate gives a logic 1 for both inputs being logic 1. A NAND gates gives a logic 0 for both inputs being a logic 1.

Simple as that! Just assume the desired output, when the input conditions are met, is a 0 instead of a 1.
• 1 person rated this as good
Not very detailed.

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### Other Answers (1)

• Member since:
February 02, 2007
Total points:
904 (Level 2)
In negative logic, logic 1 ls a low and logic 0 is a high, so just replace L with 1 and H with 0 and simplify the same way