Chapter 3 Gate-Level Minimization

3.1 Introduction The purposes of this chapter To understand the underlying mathematical description and solution of the problem To enable you to execute a manual design of simple circuits To prepare you for skillful use of modern design tools Introduce a HDL that is used by modern design tools

3.2 The Map Method Karnaugh map (K-map) Pictorial form of a truth table To present a visual diagram of a function expressed in standard form

Two-variable Map

Example: f(x,y) = m1+m2+m3 = x’y+xy’+xy = x + y

Three-variable Map

Example 3-1

Example 3-2

Example 3-3

Example 3-4

3.3 Four-Variable Map

The Adjacent Squares of Four-Variable Map One square: one minterm, a term of four literals Two adjacent squares: a term of three literals Four adjacent squares: a term of two literals Eight adjacent squares: a term of one literal Sixteen adjacent squares: 1

Example 3-5

Example 3-6

PI and EPI A prime implicant(PI) An essential PI (EPI) a product term obtained by combining the maximum possible number of adjacent sqaures in the K-map An essential PI (EPI) If a minterm in a square is covered by only one PI.

Example F(A,B,C,D) =(0,2,3,5,7,8,9,10,13,15)

3.4 Five-Variable Map

Relationship between Squares and Literals

Example 3-7

3.5 Product of Sums Simplification Get F’ by 0’s Apply DeMorgan’s theorem to F’

Example 3-8 Simplify the following Function into SOP and POS F(A,B,C,D)= (0,1,2,5,8,9,10)

Example 3-8 (con’t) F = B’D’+B’C’+A’C’D’ F’ = AB + CD + BD’

Implementation of Example 3-8

How to express the Table 3-2

How to express the Table 3-2 (con’t) F(x,y,z) = ∑ (1,3,4,6) F(x,y,z) = ∏ (0,2,5,7)

Map for the Function of Table 3-2 F= x’z+xz’ F’=xz+x’z’  F=(x’+z’)(x+z)

3.6 Don’t Care Conditions A don’t care minterm is a combination of variables whose logical value is not specified. The don’t care minterms may be assumed to be either 0 or 1. An X is used for representing the don’t care minterm.

Example 3-9

3.7 NAND and NOR Implementation The NAND or the NOR gate Universal gate Basic gates of used in all IC digital families

Why is the NAND Gate Universal?

Two Graphic Symbols for NAND Gate

Two-Level Implementation

Example 3-10

Multilevel NAND Circuits

Implementation of F=(AB’+A’B)(C+D’)

Why is the NOR Gate Universal?

Two Graphic Symbols for NOR Gate

3.8 Other Two-Level Implementation Wired-AND logic Wired-OR logic

AND-OR-INVERT

OR-AND-INVERT

Tabular Summary

Example 3-11

3.9 Exclusive-OR Function x  y = xy’+x’y (x  y)’ =xy+x’y’ x  0 = x x  1 = x’ x  x = 0 x  x’ = 1 x  y’ = x’  y = (x  y)’ A  B = B  A (A B) C = A (B C) = A B C

XOR Implementation

Map for a 3-Input Odd function and Even function

3-Input Odd and Even Functions

Map for a 4-Input Odd function and Even function

Even Parity Generator

Even Parity Checker

Logic Diagram of a Parity Generator and Checker

3.10 Hardware Description Language (HDL) HDL : a documentation language Logic simulator: representation of the structure and the behavior of a digital logic systems through a computer Logic synthesis: the process of driving a list of components and their connections from the model of a digital system described in HDL

Two Standard HDLs Supported by IEEE VHDL Verilog HDL : is chosen for this book

Verilog HDL module endmodule // : comment notation input output wire and or not # time unit `timescale: compiler directive

HDL Example 3.2 module circuit_with_delay (A,B,C,x,y); input A,B,C output x,y; wire e; and #(30) g1(e,A,B); or #(20) g3(x,e,y); not #(10) g2(y,C); endmodule

HDL Example 3-3 module simcrct; reg A, B, C; wire x, y; circuit_with_delay (A,B,C,x,y); initial begin A = 1 `b0; B = 1`b0; C=1`b0; #100 A = 1 `b1; B = 1`b1; C=1`b1; #100 $finish end endmodule

User-Defined Primitives primitive endprimitive table endtable HDL Example 3-5