0195136047.pdf

6 Digital Building Blocks and Computer Systems

6.1 Digital Building Blocks

6.2 Digital System Components

6.3 Computer Systems

6.4 Computer Networks

6.5 Learning Objectives

6.6 Practical Application: A Case Study—Microcomputer-Controlled Breadmaking Machine

Problems

Whereas a continuous change from one value to another is the essential characteristic of an

analog signal andcontinuous-state (analog) circuitsare used to process analog signals, signals

represented bydiscrete amplitudesatdiscrete timesare handled bydiscrete-state (digital) circuits.

Analog systemsprocess the information contained in the time function, which defines the signal,

whereasdigital systems,as the name implies, process digits, i.e., pulse trains, in which the

information is carried in the pulse sequence rather than the amplitude–time characterization of the

pulses. Figure 6.0.1 illustrates continuous signals, whereas Figure 6.0.2 depicts discrete signals.

Consider Figure 6.0.1(a) to be a voltage signal (as a function of a continuous-time variable

t) representing a physical quantity, such as the output voltage of a phonograph cartridge. The

discrete signal (which exists only at specific instances of time) of Figure 6.0.2(a) has the same

amplitude at timest=0,T 1 ,T 2 , andT 3 as does the continuous signal of Figure 6.0.1(a). Figure

6.0.2(a) represents thesampled-data signalobtained by sampling the continuous signal at periodic

intervals of time. The sequence of pulses in each time interval in Figure 6.0.2(b) is a numeric,

or digital, representation of the corresponding voltage samples shown in Figure 6.0.2(a). Figure

6.0.1(b) may be considered as the signal, called a clock, which sets the timing sequence used in

the generation of the pulses shown in Figure 6.0.2.

Ananalog signalis an electric signal whose value varies in analogy with a physical quantity

such as temperature, force, or acceleration. Sampling of an analog signal makes it discrete in time.

Adigital signal, on the other hand, can only have afinite number of discrete amplitudesat any

given time. Through a process known asquantization, which consists of rounding exact sample

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