CEC 220 Digital Circuit Design Boolean Algebra I Wed, Sept 2 CEC 220 Digital Circuit Design Slide 1 of 13

Lecture Outline Wed, Sept 2 CEC 220 Digital Circuit Design Introduction Basic Operations: NOT, AND, OR Representations of Boolean Expressions Slide 2 of 13

Boolean Algebra Introduction Wed, Sept 2 CEC 220 Digital Circuit Design Boolean Algebra In 1849 George Boole published a scheme for the algebraic description of logic processes In the 1930’s Claude Shannon used Boolean Algebra to describe circuits built with switches Boolean Algebra is an effective tool for describing logic circuits Slide 3 of 13

Boolean Algebra Boolean Logic Wed, Sept 2 CEC 220 Digital Circuit Design Two logic levels  TRUE = HIGH = 1  FALSE = LOW = 0 +5 V Time Transition from logic 1 to logic 0 does not take place instantaneously in real digital systems +5 V 0 Logic 1 Logic 0 Intermediate values may be visible for an instant Time Slide 4 of 13

Boolean Algebra Basic Operations: NOT, AND, OR Wed, Sept 2 CEC 220 Digital Circuit Design Logical NOT  Description: o The output is the complement/inverse/opposite of the input  Symbolic Representation (NOT gate):  Truth Table Representation:  Boolean Description: C = NOT A AC AC AC FT TF or C = A’ Slide 5 of 13

Boolean Algebra Basic Operations: NOT, AND, OR Wed, Sept 2 CEC 220 Digital Circuit Design Logical AND  Description: o The output is TRUE if and only if all the inputs are TRUE  Symbolic Representation (AND gate):  Truth Table Representation:  Boolean Description: C = A AND B ABC ABC FFF FTF TFF TTT or C = A  B or C = A B Slide 6 of 13

Boolean Algebra Basic Operations: NOT, AND, OR Wed, Sept 2 CEC 220 Digital Circuit Design Logical OR  Description: o The output is TRUE if any of the inputs are TRUE  Symbolic Representation (OR gate):  Truth Table Representation:  Boolean Description: C = A OR B ABC ABC FFF FTT TFT TTT or C = A + B This is NOT addition!! Slide 7 of 13

Boolean Algebra Logic Gates and Boolean Expressions Wed, Sept 2 CEC 220 Digital Circuit Design Derive an expression for the output of this logic circuit?  Eventually we will omit the “  ” in the AND gate and “+” in the OR gate The logic expression is a function of three variables (A, B, and C). B’ A  B’ A  B’+C Higher precedence!! Lower precedence!! Slide 8 of 13

Boolean Algebra Logic Gates and Boolean Expressions Wed, Sept 2 CEC 220 Digital Circuit Design C+D A(C+D) BE Slide 9 of 13

Boolean Algebra Logic Gates and Boolean Expressions Wed, Sept 2 CEC 220 Digital Circuit Design Literals  Each appearance of a variable or its complement in an expression is referred to as a literal.  Example:  The expression has three variables (A, B, and C)  The expression has 10 literals AB’C+A’B+A’BC’+B’C’ Slide 10 of 13

Boolean Algebra Truth Tables of a Logic Circuit Wed, Sept 2 CEC 220 Digital Circuit Design Determine the truth table for the output (F) of the logic circuit AB A’ F=A’+B Two variables  Four possible inputs (i.e. 2 n ) Truth table lists ALL possible inputs and associated outputs Slide 11 of 13

A+C Boolean Algebra Truth Tables of a Logic Circuit Wed, Sept 2 CEC 220 Digital Circuit Design Determine the truth table for the output of the logic circuit B’+C A+CB’+C(A+C)(B’+C) B’ A B C Slide 12 of 13

Next Lecture Wed, Sept 2 CEC 220 Digital Circuit Design Basic Boolean Theorems Implementation of Boolean Expressions Slide 13 of 13