Review: ALU, Latches, and Flip Flops

Review: ALU, Latches, and Flip Flops CS 231 Review October 12, 2007 Slides adapted from Sangkyum Kim

Announcements • HW 5 is released • Due at 5:00pm on 10/15/2007 (Mon) • Contains one LogicWorks problem • Grades through HW4 • Should be in Mallard • Today (10/12) • Deadline to drop semester course

Agenda • ALU • Latches • Flip-Flops

ALU Motivation Basic 4-bit adder: S = A + B + CI Adder-subtractor: G = X + Ywhen Sub= 0 G = X – Y when Sub = 1

ALU Motivation

Table of arithmetic functions

Mapping the table to an adder

Building the input logic Ai = S2Yi’ + S1Yi

Primitive gate implementation Ai = S2Yi’ + S1Yi

Quiz10 Q3

Basic Latches SR Latch S’R’ Latch

Advanced Latches SR Latch with a control input D Latch

Latches Gate delay = 1 ns

Latches

Flip Flops and Characteristic Tables Q(t+1) = D Q(t+1) = K’Q(t) + JQ’(t) Q(t+1) = T’Q(t) + TQ’(t) = T  Q(t)

Example Implement a JK flip-flop using a D flip-flop and primitive gates.

Example Implement a JK flip-flop using a D flip-flop and primitive gates. K 0 1 0 0 1 1 0 1 J Q

Example Implement a JK flip-flop using a D flip-flop and primitive gates. K 0 1 0 0 1 1 0 1 J Q D = Q K’ + Q’ J

Review: ALU, Latches, and Flip Flops