Contemporary Logic Design Weebly

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The Addison Wesley Web Page for Contemporary Logic Design. randy cs Berkeley edu,Last updated 31 July 1996,Introduction. Any change in whatever,direction for whatever There is nothing permanent. reason is strongly to be except change,deprecated,Heraclitus. Introduction, Computer hardware has experienced the most dramatic improvement in capabilities and costs ever. known to humankind In just 40 years we have seen room sized computers with little more processing. power than today s pocket calculators evolve into fingernail sized devices with near supercomputer. performance This miracle has been made possible through advances in digital hardware which now. pervades all aspects of our lives Just think how the lowly rotary telephone has become the cordless. automated answering machine It can digitize your greeting remember your most frequently dialed. numbers and allow you to review save and erase your phone messages. This book will teach you the fundamental techniques for designing and implementing complex systems. A system has inputs and outputs and exhibits explicit behavior characterized by functions that translate. the inputs into new outputs Design is the process by which incomplete and inexact requirements and. specifications describing the purpose and function of an object are made precise Implementation uses. this precise description to create a physical product You can see design and implementation in. everything around you buildings cars telephones furniture and so on. This book is about the fundamental techniques used to design and implement what we call synchronous. digital hardware systems What does each of these words mean A hardware system is one whose. physical components are constructed from electronic building blocks rather than wood plastic or steel. A hardware system can be digital or analog The inputs and outputs of a digital system fall within a. discrete finite set of values In an analog system the outputs span a continuous range In this book we. concentrate on systems in the digital domain A synchronous system is one whose elements change their. values only at certain specified times An asynchronous system has outputs that can change at any time. It is safer and more foolproof to build our systems using synchronous methods which is the focus of this. To see the difference between synchronous and asynchronous systems think of a digital alarm clock. Suppose that the alarm is set for 11 59 and the alarm sounds when the time readout exactly matches. 11 59 In a synchronous system the outputs all change at the same time The clock advances from 10 59. to 11 00 to 11 01 and so on In an asynchronous system the hours and minutes are not constrained to. change simultaneously So looking at the clock you might see it advance from 10 59 to 11 59. momentarily to 11 00 And of course this would make the alarm sound at the wrong time. You can best understand complex hardware systems in terms of descriptions of increasing levels of. detail Moving from the abstract to the most detailed these levels are called system logic and circuit. The system level abstractly describes the input output and behavior A system level description. focuses on timing and sequencing using flowcharts or computer programs The logic level deals with the. composition of building blocks called logic gates which form the physical components used by system. designers At the circuit level the building blocks are electrical elements such as transistors resistors. and capacitors which implement the logic designer s components Thus abstract system descriptions are. built upon logic descriptions which in turn depend on detailed circuits. This book is primarily for logic designers but to learn logic design you must also know something about. system and circuit design What are the best logic building blocks to support the system designer How. are they constructed from the available electrical elements What kinds of blocks are needed How. much does it cost to build them We approach the material from the perspective of computer science. rather than electrical engineering the only prerequisite knowledge we assume is an understanding of. binary numbers basic electronics and some limited familiarity with a programming language such as C. or PASCAL You can review binary numbers in Appendix A and basic electronics in Appendix B. New technology is making this an exciting time for hardware designers Traditionally they have had to. build their hardware before being able to check for proper behavior This situation is undergoing radical. change because of the new technology of rapid prototyping Designers use computer programs called. computer aided design CAD tools to help create implementations and verify their behavior before. actually building them, Even the basic logic components used in hardware implementation are undergoing change In.
conventional logic design the building blocks perform fixed unchangeable functions Today they are. being replaced by flexible logic building blocks whose function can be configured for the job at hand. This remarkable technology is called programmable logic and you will learn how to use it in your. Hardware design is the art of the possible creatively finding the balance between the requirements of. systems on one side and the opportunities provided by electronic components on the other But first you. need to understand the basics of the design process so let s begin there. 1 The Process of Design,2 Digital Hardware Systems. 3 Multiple Representations of a Digital Design,4 Rapid Electronic System Prototyping. Chapter Review,Table of Contents Next Prev,This file last updated on 05 19 96 at 09 31 39. randy cs Berkeley edu,Top Next Prev,1 1 The Process of Design. Design is a complex process more of an art than a science It is not simply a matter of following. predetermined steps as in a recipe The only way to learn design is to do design Let s introduce the. concept with an example Your boss has given you the job of designing and implementing a simple. device to control a traffic light, So how do you begin Figure 1 1 portrays the three somewhat overlapping phases through which every.
design project must pass design implementation and debugging Not surprisingly these are the same. whether the object being designed is a complex software system an engineering system like a power. plant or an electronic system like a computer Let s look at each of these phases in more detail. 1 1 1 Design as Refinement of Representations, Complex systems can be described from three independent viewpoints which we shall call functional. structural and physical The functional view describes the behavior of the system in terms of its inputs. and outputs The structural view describes how the system is broken down into ever more primitive. components that form its implementation Finally the physical view describes the detailed placement. and interconnection of the primitive building blocks that make up the implementation You can think of. design as a process of precisely and creatively determining these aspects. To illustrate these concepts consider a simplified representation of a car Its inputs are gasoline and the. positions of the accelerator pedal brake pedal and steering wheel Its output is the power that moves the. vehicle in a given direction with a given speed The detailed specification of how the inputs determine. the direction and speed of the car constitutes its functional description. The car system can be broken down into major interacting subsystems such as the engine and the. transmission These are made up of their own more primitive components For example the engine. consists of carburetion and cooling subsystems This is the structural description. At the most detailed level the subsystems are actually primitive physical components screws metal. sheets pipes and so forth The car s cooling subsystem can be described in terms of a radiator water. reservoir rubber tubing and channels through the engine block These form the physical representation. of the car, Design Specification Let s return to our hardware example the traffic light controller Your design. begins with understanding what you want to design and the constraints on its implementation This is the. design specification Your goal is to obtain a detailed and precise functional description from the design. specification, You begin by determining the system s inputs and outputs Then you identify the way the outputs are. derived from the inputs You would probably start by asking your boss about the traffic light s functional. capabilities Here is what your boss tells you, The traffic light points in four directions call them N S E W. It always illuminates the same lights on N as S and E as W. It cycles through the sequence green yellow red, N S and E W are never green or yellow at the same time.
The lights are green for 45 seconds yellow for 15 red for 60. You can see that the inputs and outputs are not described explicitly here but a little thought should help. Since each light must be turned on or off there must be one output for each color green yellow red. and each direction East West North South That s 12 different outputs Not all of these are unique. Since North and South are identical as are East and West the number of unique outputs is six. But what are the inputs Something has to tell the system when to start processing We call this the. start or more commonly the reset signal In addition the system must be equipped with some periodic. signals to indicate that 15 or 45 seconds have elapsed These signals are often called clocks The inputs. could be represented by two independent clocks or by a single 15 second clock with additional hardware. to count one or three ticks Since your boss has not specified this in detail it is up to you to decide It. is not unusual for the initial design specification to be ambiguous or incomplete The designer must. make critical decisions to complete the specification This is part of the creativity demanded of the. designer filling in the details of the designs subject to the specified constraints. How are the inputs and outputs related There are many ways to represent the functional behavior of a. system such as the flowchart shown in Figure 1 2 The start signal causes the green N S lights and the. red E W lights to be illuminated When the 45 second clock tick arrives new outputs are turned on the. N S green lights go off the yellow lights go on and the E W lights stay red After another 15 second. clock tick N S yellow goes off N S red goes on E W red goes off and E W green goes on A similar. sequence of events happens when the light configuration changes to N S red E W green and then to N. S red and E W yellow After this the whole process repeats. Design Constraints At this point you have a pretty good feeling about the function of the traffic light. The next set of issues deals with the system s performance characteristics You need to consider the. operational speed of the hardware the amount of space it takes up the amount of power it consumes. and so on These are called the design s performance metrics Constraints on performance influence the. design by forcing you to reject certain design approaches that violate the constraints. So now you must go back to ask the boss a few questions How fast must the hardware be How much. can it cost How small does it have to be What is the maximum power it can consume Answering. these ques tions will help you identify the appropriate implementation approach. The traffic light system changes its outputs every few seconds Your boss tells you that a very slow. inexpensive technology can be used, The traffic light hardware must fit in a relatively small box to be placed next to the structural support for. the lights Your boss tells you that a 6 inch by 6 inch by 1 inch space is available for the hardware You. recognize that old fashioned oversized vacuum tubes are out but neither is an advanced technology. needed For the kinds of technologies we will be describing in this book this space could hold. approximately 20 components, How much can it cost Erecting a set of traffic lights probably costs several thousand dollars Despite. this your boss tells you that the hardware cannot exceed 20 in total component cost This rules out the. hottest microprocessor currently available which costs a few hundred dollars but the constraint. should be easy to meet with simple inexpensive components. How much power can the system consume The boss limits you to less than 20 watts about one third of. the power consumed by a typical light bulb At this power level you won t have to worry about fans. If a given component consumes less than 1 watt the power and area constraints together restrict your. design to no more than 20 components At a dollar a component the design should also be able to meet. the cost constraint, Design as Representation Design is a complicated business It has been said that to design is to. represent Our initial representation of the traffic light controller was a rather imprecise set of. constraints expressed in English We refine this into something more detailed and precise suitable for. implementation We start by identifying the system s inputs and outputs Then we obtain a more formal. behavioral description such as the flowchart shown in Figure 1 2 Ultimately we refine the design to a. level of detail that can be implemented directly by the primitive building blocks of our chosen. Contemporary Logic Design Randy H Katz University of California Benjamin Cummings Addison Wesley Publishing Company 1993 Table of Contents 1 Introduction 2 Two Level Combinational Logic 3 Multilevel Combinational Logic 4 Programmable and Steering Logic 5 Arithmetic Circuits 6 Sequential Logic Design 7 Sequential Logic Case Studies 8 Finite State Machine Design 9 Finite State Machine

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