2 Chapter 1 Introduction may be applied in ways that have not even been discovered yet.As for practices. they may be from what's presented here by the time you start working in the field,and they will certainly continue to change throughout your career.So you should treat the "practices"material in this book as a way to rein- force principles,and as a way to leam design methods by example. One of the book's goals is to present enough about basic principles for you to know what's happening when you use software tools to turn the crank for you. The same basic principles can help you get to the root of problems when the tools happen to get in your way. Listed in the box on this page,there are several key points that you should learn through your studies with this text.Most of these items probably make no sense to you right now,but you should come back and review them later. Digital design is engineering,and engineering means"problem solving." My experience is that only 5%-10%of digital design is "the fun stuff"-the is much easier now than it was 20 or even 10 years ago,but you still can't spend 100%or even 50%of your time on the fun stuff. IMPORTANT Good tools do not guarantee good design,but they help a lot by taking the pain out THEMES IN of doing things right. DIGITAL DESIGN Digital circuits have analog characteristics Know when to worry and when not to worry about the analog aspects of digital design Always document your designs to make them understandable by yourselfand others Associate active levels with signal names and practice bubble-to-bubble logi design Understand and use standard functional building blocks Design for minimum cost at the system level,including your own engineering effort as part of the cost. State-machine design is like programming;approach it that way. Use programmable logic to simplify designs,reduce cost,and accommodate last- .Avoid asynchronous design.Practice synchronous design until a better methodology comes along Pinpoint the unavoidable asynchronous interfaces between different subsystems and the outside world,and provide reliable synchronizers. Catching a glitch in time saves nine Copyright1999 by John F.Wakerly Copying Prohibited 2 Chapter 1 Introduction DO NOT COPY DO NOT COPY DO NOT COPY DO NOT COPY DO NOT COPY DO NOT COPY DO NOT COPY DO NOT COPY DO NOT COPY Copyright © 1999 by John F. Wakerly Copying Prohibited may be applied in ways that have not even been discovered yet. As for practices, they may be a little different from what’s presented here by the time you start working in the field, and they will certainly continue to change throughout your career. So you should treat the “practices” material in this book as a way to rein￾force principles, and as a way to learn design methods by example. One of the book's goals is to present enough about basic principles for you to know what's happening when you use software tools to turn the crank for you. The same basic principles can help you get to the root of problems when the tools happen to get in your way. Listed in the box on this page, there are several key points that you should learn through your studies with this text. Most of these items probably make no sense to you right now, but you should come back and review them later. Digital design is engineering, and engineering means “problem solving.” My experience is that only 5%–10% of digital design is “the fun stuff”—the creative part of design, the flash of insight, the invention of a new approach. Much of the rest is just “turning the crank.” To be sure, turning the crank is much easier now than it was 20 or even 10 years ago, but you still can’t spend 100% or even 50% of your time on the fun stuff. IMPORTANT THEMES IN DIGITAL DESIGN • Good tools do not guarantee good design, but they help a lot by taking the pain out of doing things right. • Digital circuits have analog characteristics. • Know when to worry and when not to worry about the analog aspects of digital design. • Always document your designs to make them understandable by yourself and others. • Associate active levels with signal names and practice bubble-to-bubble logic design. • Understand and use standard functional building blocks. • Design for minimum cost at the system level, including your own engineering effort as part of the cost. • State-machine design is like programming; approach it that way. • Use programmable logic to simplify designs, reduce cost, and accommodate last￾minute modifications. • Avoid asynchronous design. Practice synchronous design until a better methodology comes along. • Pinpoint the unavoidable asynchronous interfaces between different subsystems and the outside world, and provide reliable synchronizers. • Catching a glitch in time saves nine