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Chapter 2 - Part 1 - PPT - Mano & Kime - 2nd Ed

Slide 1 Lecture 5 Basics of Boolean Algebra

Lecture 5 Basics of Boolean Algebra

Slide 2 Outline

Outline Boolean Algebra Boolean Properties and Identities Boolean Algebraic Proofs Useful Theorems Algebraic Simplification Complementing Functions Function Evaluation

Slide 3 Boolean Algebra

1. 3. 5. 7. 9. 11. 13. 15. 17. Commutative Associative Distributive DeMorgan s 2. 4. 6. 8. X . 1 X = X . 0 0 = X . X X = 0 = X . X Boolean Algebra An algebraic structure defined on a set of at least two elements, B, together with three binary operators (denoted +, · and ) that satisfies the following basic identities: 10. 12. 14. 16. X + Y Y + X = (X + Y) Z + X + (Y Z) + = X(Y + Z) XY XZ + = X + Y X . Y = XY YX = (XY) Z X(Y Z) = X + YZ (X + Y) (X + Z) = X . Y X + Y = X + 0 X = + X 1 1 = X + X X = 1 = X + X X = X Define existence Of 0 and 1 Idempotence Existence of Complement Involution Dual Functions: Swap +/ · Swap 0/1

Slide 4 Some Properties of Identities & the Algebra

The identities above are organized into pairs. These pairs have names as follows: 1-4 Existence of 0 and 1 5-6 Idempotence 7-8 Existence of complement 9 Involution 10-11 Commutative Laws 12-13 Associative Laws 14-15 Distributive Laws 16-17 DeMorgan s Laws If the meaning is unambiguous, we leave out the symbol · Some Properties of Identities & the Algebra The dual of an algebraic expression is obtained by interchanging + and · and interchanging 0 s and 1 s. The identities appear in dual pairs. When there is only one identity on a line the identity is self-dual, i. e., the dual expression = the original expression.

Slide 5 Some Properties of Identities & the Algebra (Continued)

Unless it happens to be self-dual, the dual of an expression does not equal the expression itself. Example: F = (A + C) · B + 0 dual F = (A · C + B) · 1 = A · C + B Example: G = X · Y + (W + Z) dual G = Example: H = A · B + A · C + B · C dual H = Are any of these functions self-dual? Some Properties of Identities & the Algebra (Continued) ((X+Y) · (W · Z)') = ((X+Y) ·(W' + Z') (A + B)(A + C)(B + C) (A + BC)(B + C) = AB + AC + BC

Slide notes

Dual G = ((X+Y) · (W · Z)') = ((X+Y) ·(W' + Z') Dual H = (A + B)(A + C)(B + C). Using the Boolean identities, = (A +BC) (B+C) = AB + AC + BC. So H is self-dual.

Slide 6 Boolean Operator Precedence

Boolean Operator Precedence The order of evaluation in a Boolean expression is: 1. Parentheses 2. NOT 3. AND 4. OR Consequence: Parentheses appear around OR expressions Example: F = A(B + C)(C + D)

Slide 7 Example 1: Boolean Algebraic Proof

Example 1: Boolean Algebraic Proof A + A·B = A (Absorption Theorem) Proof Steps Justification A + A·B = A · 1 + A · B X = X · 1 = A · ( 1 + B) X · Y + X · Z = X ·(Y + Z) (Distributive Law) = A · 1 1 + X = 1 = A X · 1 = X Our primary reason for doing proofs is to learn: Careful and efficient use of the identities and theorems of Boolean algebra, and How to choose the appropriate identity or theorem to apply to make forward progress, irrespective of the application.

Slide 8 Example 2: Boolean Algebraic Proofs

AB + A C + BC = AB + A C (Consensus Theorem) Proof Steps Justification AB + A C + BC = AB + A C + 1 · BC 1 . X = X = AB + A C + (A + A ) · BC X + X = 1 = AB + A C + ABC + A BC X(Y + Z) = XY + XZ (Distributive Law) = AB + ABC + A C + A BC X + Y = Y + X (Commutative Law) = AB . 1 + ABC + A C . 1 + A C . B X . 1 = X, X . Y = Y . X (Commutative Law) = AB (1 + C) + A C (1 + B) X(Y + Z) = XY +XZ (Distributive Law) = AB . 1 + A C . 1 = AB + A C X . 1 = X Example 2: Boolean Algebraic Proofs

Slide notes

Justification 1: 1 . X = X Justification 2: X + X = 1 = AB + A C + ABC + A BC X(Y + Z) = XY + XZ (Distributive Law) = AB + ABC + A C + A BC X + Y = Y + X (Commutative Law) = AB . 1 + ABC + A C . 1 + A C . B X . 1 = X, X . Y = Y . X (Commutative Law) = AB (1 + C) + A C (1 + B) X(Y + Z) = XY +XZ (Distributive Law) = AB . 1 + A C . 1 = AB + A C X . 1 = X

Slide 9 Useful Theorems

x y × y Useful Theorems ( ) ( ) n inimizatio M y y y x y y y x = + + = × × ( ) tion Simplifica y x y x y x y x × = + × + = × + Consensus z y x z y z y x × + × = × + × + × ( ) ( ) ( ) ( ) ( ) z y x z y z y x + × + = + × + × + Laws s DeMorgan' x x × = + + x x x x x x x x y x = + y

Slide 10 Expression Simplification

Expression Simplification An application of Boolean algebra Simplify to contain the smallest number of literals (complemented and uncomplemented variables): = AB + ABCD + A C D + A C D + A B D = AB + AB(CD) + A C (D + D) + A B D = AB + A C + A B D = B(A + AD) +AC = B (A + D) + A C 5 literals + + + + D C B A D C A D B A D C A B A Absorption: X + XY = X Simplification: X + X Y = X + Y

Slide 11 Complementing Functions

Complementing Functions Use DeMorgan's Theorem to complement a function: 1. Interchange AND and OR operators 2. Complement each constant value and literal    Example: Complement F = F = (x + y + z)(x + y + z) x + z y z y x

Slide notes

Slide 12 Boolean Function Evaluation

Boolean Function Evaluation z x y x F4 x z y x z y x F3 x F2 xy F1 + = + = = = z y z + y + 1 0 0 1 1 1 0 0 0 1 0 1 1 1 0 0 0 0 0 0 0 0 1 0 0 1 0 0 1 1 1 1

Slide notes

F3 is 1 for x y z , x yz, xy z and xy z => F3 = 1,0,0,1,1,1,0,0 F4 is 1 for xy z , xy z, x y z and x y z => F4 = 0,1,0,1,1,1,0,0

Slide 13 Summary

Summary Boolean Algebra Boolean Properties and Identities Boolean Algebraic Proofs Useful Theorems Algebraic Simplification Complementing Functions Function Evaluation

End of slides

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