# Logic Gate Help Brain Fart

Discussion in 'Homework Help' started by JosephB, Oct 6, 2016.

1. ### JosephB Thread Starter New Member

Oct 6, 2016
1
0
Hello all, I am having some trouble with this simple expression, Im not really sure why, I think I need another set of eyes Ive been staring at these stupid letters all day they are starting to blend in. The equation is in the first picture and the circuit I created is in the second picture, can someone help me find my silly little error.

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Jun 8, 2013
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Hi

3. ### WBahn Moderator

Mar 31, 2012
17,715
4,788
@eetech00 Please don't just do someone's homework for them.

The overwhelming convention, particularly in EE, is that logical AND has precedence over logical OR. Thus there is a difference between

( (AD)' + B )( C' + A )

and

( AD' + B( C' + A ) )

4. ### WBahn Moderator

Mar 31, 2012
17,715
4,788
Why do you think that your solution is incorrect?

How have you been told to interpret

Y = A + BC

Is it the same as

Y = A OR (B AND C)

or is it

Y = (A OR B) AND C

The former is almost always what is taught (namely that logical AND has precedence over logical OR) and this is reinforced by the arithmetic multiplication/addition operators that are used for these logical operators. But others point out that basic Boolean algebra imposes no such precedence and thus they are of equal precedence and should be performed strictly from left to right. However, these people conveniently ignore the fact that Boolean algebra also imposes no associativity for these operations either in which case the order of evaluation is undefined unless imposed by parentheses.

My very confident guess is that you have been taught to treat AND as having higher priority than OR. Since both operations are independently associative, that then becomes a non-issue.