Logical Systems Synthesis Logical Synthesis Basic Gate Synthesis

Logical Systems Synthesis

Logical Synthesis

Basic Gate Synthesis f=a. b f=a+b f = a’

Basic Gate Synthesis f = (a. b)’ f = (a + b)’ f=a

Operator Precedence in Synthesis F=A+B. C Incorrect Correct

Operator Precedence in Synthesis F = (A + B). C Correct Incorrect

An example of Step by Step Synthesis Single Output Circuits

F = A + (B’ + C)(D’ + BE’) Reducing it to a more abstract form P = BE’ M = B’ + C F = A + M(D’ + P) N = D’ + P F = A + MN Z = MN F=A+Z

F=A+Z

F=A+Z F = A + MN

F=A+Z F = A + MN F = A + M(D’ + P)

An example of Multi-Output Synthesis

Sharing Gates f = ab + a’c g = ab + a’c’ These are the common terms in both logic expressions, therefore, they can be used to as a common gate when synthesizing the complete digital system.

Idea of sharing of Gates f = a’c + ab g = a’c’ + ab Circuits for f and g have a common product term (Implicant) namely ab. We are going to make it a common factor i. e. we are going to use the corresponding gate to drive both outputs f & g.

Symbols

From Digital Design, 5 th Edition by M. Morris Mano and Michael Ciletti

Boolean Algebra Manipulation of Switching Functions Boolean/Logic/Switching Expression/Function

Boolean Functions • Variables and constants take on only one of the two values : 0 or 1 • There are three operators – OR – AND – NOT written as a+b a. b a’

Operator Precedence () Precedence Sequence ’. +

Metatheorem A Theorem about Theorems Duality Any Theorem or Identity in Switching Algebra remains true if 0 & 1 are swapped and. & + are swapped throughout the expression Note: Duality does not imply logical equivalence. It only states that one fact leads to another fact.

Axioms / Postulates 0. 0=0 1+1=1 1. 1=1 0+0=0 0. 1=1. 0=0 0+1=1+0=1 x = 0 implies x’ = 1 x = 1 implies x’ = 0

Theorems (Single Variable) Null Elements x. 0=0 x+1=1 Identities x. 1=x x+0=x Idempotency x. x=x x+x=x Complements x. x’ = 0 x + x’ = 1 Involution (x’)’ = x

Theorems (2 - & 3 - Variable) Commutativity x. y=y. x x+y=y+x Associativity x. (y. z) = (x. y). z x + (y + z) = (x + y) + z Distributivity x. (y + z) = x. y + x. z x + (y. z) = (x + y). (x + z) Covering x + (x. y) = x x. (x + y) = x Combining (x. y) + (x. y’) = x (x + y). (x + y’) = x

Theorems (2 - & 3 - Variable) De. Morgan’s Theorem (x. y)’ = x’ + y’ (x + y)’ = x’. y’ Consensus Theorem (x. y) + (x’. z) + (y. z) = (x. y) + (x’. z) (x + y). (x’ + z). (y + z) = (x + y). (x’ + z)

Theorems (n-Variable) Generalized Idempotency x. x. -----. x = x x + ----- + x = x De. Morgan’s Theorem (x 1. x 2. -----. xn)’ = x 1’ + x 2’ + ----- + xn’ (x 1 + x 2 + ----- + xn)’ = x 1’. x 2’. -----. xn’

Theorems (n-Variable) Generalized De. Morgan’s Theorem [F(x 1, x 2, -----, xn, . , + )]’ = F(x 1’, x 2’, -----, xn’, + , . )

Implications of De. Morgan’s Theorem f = ( a. b )’ = a’ + b’ f = ( a + b )’ = a’. b’

Function Manipulation Using Axioms and Theorems of Boolean Algebra

Proof of Consensus Theorem x. y + x’. z + y. z = x. y + x’. z + y. z. 1 = x. y + x’. z + y. z. (x + x’) = x. y + x’. z + x. y. z + x’. y. z = x. y. 1 + x. y. z + x’. z. 1 + x’. y. z = x. y. (1 + z) + x’. z. (1 + y) = x. y. 1 + x’. z. 1 = x. y + x’. z Theorem Used a = a. 1 1 = a + a’ a. (b + c) = a. b + a. c a = a. 1 a. b + a. c = a. (b + c) 1+a=1 a. 1 = a

Find De. Morgan’s Equivalent of the Following

De. Morgan’s Equivalent F = ( ( B. E’ ) + D’ ). ( B’ + C ) + A

De. Morgan’s Equivalent F’ = ( B’ + E ). D ) + ( B. C’ ). A’

Using De. Morgan’s Theorem NAND NOR Inter-Conversion A circuit developed using NAND gates only can be converted into a circuit employing only NOR gates by directly replacing the NAND gates with the NOR gates and inverting all the inputs and outputs of the circuit The Converse of this operation is also true

F = A + (B’ + C). (D’ + B. E’) Can also be written in the following notation F = A + (B’ + C)(D’ + BE’)

Forms of Logic Expressions

Generalized Forms of Logic Expressions SOP Sum of Products POS Product of Sums

Terminology Literal Sum Term Product of Sums Sum of Products

Definitions • Literal – A variable in either it’s complemented or uncomplemented form • Sum Term – One or more Literals connected by an OR operator • Product Term – One or more Literals connected by an AND operator

Definitions • Product of Sums – One or more Sum Terms connected by an AND operator • Sum of Products – One or more Product Terms connected by an OR operator

SOP Expression

POS Expression

More SOP Expressions ABC + A’BC’ AB + A’BC’ + C’D’ + D A’B + CD’ + EF + GK + HL’ More POS Expressions (A + B’ + C)(A + C) (A + B’)(A’ + C’ + D)F’ (A + C)(B + D’)(B’+C)(A + D’ + E)

Canonical Forms of Logic Expressions C-SOP Sum of Standard Product Terms aka Canonical Sum C-POS Product of Standard Sum Terms aka Canonical Product

More Terminology Minterm Maxterm Canonical Sum Canonical Product

Definitions • Minterm aka Standard Product Term – A Product Term composed of all the variables of the given problem • Maxterm aka Standard Sum Term – A Sum Term composed of all the variables of the given problem

Definitions • Canonical Sum – One or more Minterms connected by an OR operator • Canonical Product – One or more Maxterms connected by an AND operator

C-SOP Expression

C-POS Expression

Writing Algebraic Expressions From Truth Tables

Decomposing into Minterms Implementing 1’s OR =

Minterms Notation

Expressions involving Minterms

Decomposing into Maxterms Implementing 0’s AND =

Maxterms Notation

Expressions involving Maxterms

Write Expressions using Minterm/Maxterm Terminology for the following Truth Table Using Minterms f =? Using Maxterms f =?

Write Expressions using Minterm/Maxterm Terminology for the following Truth Table Using Minterms f = m 2 + m 5 + m 6 Using Maxterms f = M 0. M 1. M 3. M 4. M 7

Write Expressions using Minterm/Maxterm Terminology for the following Truth Table Using Minterms f = m 2 + m 5 + m 6 f’ = ? Using Maxterms f = M 0. M 1. M 3. M 4. M 7 f’ = ?

Write Expressions using Minterm/Maxterm Terminology for the following Truth Table Using Minterms f = m 2 + m 5 + m 6 f’ = m 0 + m 1 + m 3 + m 4 + m 7 Using Maxterms f = M 0. M 1. M 3. M 4. M 7 f’ = M 2. M 5. M 6

Write Expressions using Minterm/Maxterm Terminology for the following Truth Table Using Minterms f = m 2 + m 5 + m 6 f’ = m 0 + m 1 + m 3 + m 4 + m 7 Using Maxterms f = M 0. M 1. M 3. M 4. M 7 f’ = M 2. M 5. M 6 Alternative Notation f = ∑ (2, 5, 6) = ∏ (0, 1, 3, 4, 7) f’ = ∏ (2, 5, 6) = ∑ (0, 1, 3, 4, 7)

Write Expressions using Minterm/Maxterm Terminology for the following Truth Table Using Minterms f =? f’ = ? Using Maxterms f =? f’ = ?

Write Expressions using Minterm/Maxterm Terminology for the following Truth Table Using Minterms f = m 1 + m 5 + m 6 + m 8 + m 9 + m 10 + m 14 + m 15 f’ = m 0 + m 2 + m 3 + m 4 + m 7 + m 11 + m 12 + m 13 Using Maxterms f = M 0. M 2. M 3. M 4. M 7. M 11. M 12. M 13 f’ = M 1. M 5. M 6. M 8. M 9. M 10. M 14. M 15

Write Expressions using Minterm/Maxterm Terminology for the following Truth Table f = ∑ (1, 5, 6, 8, 9, 10, 14, 15) f = ∏ (0, 2, 3, 4, 7, 11, 12, 13) f’ = ∑ (0, 2, 3, 4, 7, 11, 12, 13) f’ = ∏ (1, 5, 6, 8, 9, 10, 14, 15)

Can you intuitively establish a relationship within the following set of results? f = m 2 + m 5 + m 6 f’ = m 0 + m 1 + m 3 + m 4 + m 7 f = M 0. M 1. M 3. M 4. M 7 f’ = M 2. M 5. M 6 f = m 1 + m 5 + m 6 + m 8 + m 9 + m 10 + m 14 + m 15 f’ = m 0 + m 2 + m 3 + m 4 + m 7 + m 11 + m 12 + m 13 f = M 0. M 2. M 3. M 4. M 7. M 11. M 12. M 13 f’ = M 1. M 5. M 6. M 8. M 9. M 10. M 14. M 15

To implement a function we can use the logic 1’s in the output to obtain a Minterms’ SOP or use the logic 0’s to obtain a Maxterms’ POS F(x 1, x 2, …. , xn) = ∑m. R = ∏MS [F(x 1, x 2, …. , xn)]’ = ∑m. S = ∏MR Where, T = {Set of all indices} = {0 to 2 n - 1} R = {Set of indices of required to implement C-SOP of F(x 1, x 2, …. , xn)} S=T–R Note : Observe the Duality inherent in this Generalization

Use Boolean Algebra to establish the relationship between the following set of Expressions f = m 2 + m 5 + m 6 f’ = m 0 + m 1 + m 3 + m 4 + m 7 f = M 0. M 1. M 3. M 4. M 7 f’ = M 2. M 5. M 6 f = m 1 + m 5 + m 6 + m 8 + m 9 + m 10 + m 14 + m 15 f’ = m 0 + m 2 + m 3 + m 4 + m 7 + m 11 + m 12 + m 13 f = M 0. M 2. M 3. M 4. M 7. M 11. M 12. M 13 f’ = M 1. M 5. M 6. M 8. M 9. M 10. M 14. M 15

Converting SOP to POS f = x y + x’ z (SOP Form) Using Distributive Law f = x y + x’ z f = ( x y + x’ ) (x y + z) f = ( x + x’ ) ( y + x’ ) ( x + z ) ( y + z ) f = ( y + x’ ) ( x + z ) ( y + z ) (POS Form)

Converting POS to SOP f = ( x + y ) ( x’ + z ) (POS Form) Using Distributive Law f = ( x + y ) ( x’ + z ) f = x ( x’ + z ) + y ( x’ + z ) f = x x’ + x z + y x’ + y z f = x z + y x’ + y z (SOP Form) Note : To obtain the expression f = x y + x’ z as in the previous slide apply Consensus Theorem

Converting SOP to C-SOP F = A + B’C (SOP Form) Expanding both terms separately using {x = x. 1} & {1 = (x + x’)} A = A (B + B’) = AB + AB’ = AB (C + C’) + AB’ (C + C’) A = ABC + ABC’ + AB’C’ B’C = B’C (A + A’) = AB’C + A’B’C Combining the expressions F = ABC + ABC’ + AB’C’ + AB’C + A’B’C = ABC + ABC’ + AB’C’ + A’B’C Using {x + x = x} F = ABC + ABC’ + AB’C’ + A’B’C (C-SOP Form)