Section1.2 Analog versus Digital 3 Besides the fun stuff and turning the crank,there are many other areas in which a successful digital designer must be competent,including the following: .Debugging.It's next to impossible to be a good designer without being a good troubleshooter.Successful debugging takes planning,a systematic approach,patience,and logic:if you can't discover where a problem is, find out where it is not! Business requirements and practices.A digital designer's work is affected by a lot of non factors,including documentation standards. component availability,feature definitions,target specifications,task scheduling,office politics,and going to lunch with vendors. Risk-taking.When you begin a design project you must carefully balance risks against potential rewards and consequences,in areas ranging from new-component selection(will it be available when I'm ready to build the first prototype?)to schedule commitments (will I still have a job if I'm late?). Communication.Eventually,you'll hand off your successful designs to other engineers,other departments,and customers.Without good commu- nication skils,you'll never complete this step successfully.Keep in mind that communication includes not just transmitting but also receiving;learn to be a good listener! In the rest of this chapter,and throughout the text,I'll continue to state smopinionsabout what's important nd what is notIthinkIietodo so as a moderately successful practitioner of digital design.Of course,you are always welcome to share your own opinions and experience (send email to john@wakerly.com) 1.2 Analog versus Digital Analog devices and systems process time-varying signals that can take on any value across a continuous range of voltage,current,or other metric.So do digita digita circuits and systems;the difference is that we can pretend that they don't!A digital signal is modeled as taking on,at any time.only one of two discrete values,which we call 0 and /(or LOW and HIGH,FALSE and TRUE,negated 0 and asserted,Sam and Fred,or whatever). Digital computers have been around since the 1940s,and have been in widespread commercial use since the 1960s.Yet only in the past 10 to 20 years has thedigital revolutionspread to many other aspects of life.Examples of once-analog systems that have now"gone digital"include the following: Still pictures.The majority of cameras still use silver-halide film to record images However,the increasing density of digital memory chips has allowed the development of digital cameras which record a picture as a Copyright 1999 by John F.Wakerly Copying ProhibitedSection 1.2 Analog versus Digital 3 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 Besides the fun stuff and turning the crank, there are many other areas in which a successful digital designer must be competent, including the following: • Debugging. It’s next to impossible to be a good designer without being a good troubleshooter. Successful debugging takes planning, a systematic approach, patience, and logic: if you can’t discover where a problem is, find out where it is not! • Business requirements and practices. A digital designer’s work is affected by a lot of non-engineering factors, including documentation standards, component availability, feature definitions, target specifications, task scheduling, office politics, and going to lunch with vendors. • Risk-taking. When you begin a design project you must carefully balance risks against potential rewards and consequences, in areas ranging from new-component selection (will it be available when I’m ready to build the first prototype?) to schedule commitments (will I still have a job if I’m late?). • Communication. Eventually, you’ll hand off your successful designs to other engineers, other departments, and customers. Without good commu￾nication skills, you’ll never complete this step successfully. Keep in mind that communication includes not just transmitting but also receiving; learn to be a good listener! In the rest of this chapter, and throughout the text, I’ll continue to state some opinions about what’s important and what is not. I think I’m entitled to do so as a moderately successful practitioner of digital design. Of course, you are always welcome to share your own opinions and experience (send email to john@wakerly.com). 1.2 Analog versus Digital Analog devices and systems process time-varying signals that can take on any value across a continuous range of voltage, current, or other metric. So do digital circuits and systems; the difference is that we can pretend that they don’t! A digital signal is modeled as taking on, at any time, only one of two discrete values, which we call 0 and 1 (or LOW and HIGH, FALSE and TRUE, negated and asserted, Sam and Fred, or whatever). Digital computers have been around since the 1940s, and have been in widespread commercial use since the 1960s. Yet only in the past 10 to 20 years has the “digital revolution” spread to many other aspects of life. Examples of once-analog systems that have now “gone digital” include the following: • Still pictures. The majority of cameras still use silver-halide film to record images. However, the increasing density of digital memory chips has allowed the development of digital cameras which record a picture as a analog digital 0 1