digital fundamentals - khon kaen universitywatis/courses/en842003/chapter1.pdfbasic system functions...

© 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10th ed

Digital Fundamentals

Tenth Edition

Floyd

© 2008 Pearson Education

Chapter 1


Most natural quantities that we see are analog and vary continuously. Analog systems can generally handle higher power than digital systems.

SummarySummary

Digital systems can process, store, and transmit data more efficiently but can only assign discrete values to each point.

Analog Quantities

1

100

A .M.

95

90

85

80

75

2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12P.M .

Temperature(°F)

70

Time of day


Many systems use a mix of analog and digital electronics to take advantage of each technology. A typical CD player accepts digital data from the CD drive and converts it to an analog signal for amplification.

SummarySummary

Analog and Digital Systems

Digital data

CD drive

10110011101

Analogreproductionof music audiosignal

Speaker

Soundwaves

Digital-to-analogconverter

Linear amplifier


Digital electronics uses circuits that have two states, which are represented by two different voltage levels called HIGH and LOW. The voltages represent numbers in the binary system.

SummarySummary

Binary Digits and Logic Levels

In binary, a single number is called a bit (for binary digit). A bit can have the value of either a 0 or a 1, depending on if the voltage is HIGH or LOW.

HIGH

LOW

VH(max)

VH(min)

VL(max)

VL(min)

Invalid


Digital waveforms change between the LOW and HIGH levels. A positive going pulse is one that goes from a normally LOW logic level to a HIGH level and then back again. Digital waveforms are made up of a series of pulses.

SummarySummary

Digital Waveforms

Falling orleading edge

(b) Negative–going pulse

HIGH

Rising ortrailing edge

LOW

(a) Positive–going pulse

HIGH

Rising orleading edge

Falling ortrailing edge

LOWt0 t1 t0 t1


Actual pulses are not ideal but are described by the rise time, fall time, amplitude, and other characteristics.

SummarySummary

Pulse Definitions

90%

50%

10%

Base line

Pulse width

Rise time Fall time

Amplitude tW

tr tf

Undershoot

Ringing

Overshoot

RingingDroop


Periodic pulse waveforms are composed of pulses that repeats in a fixed interval called the period. The frequency is the rate it repeats and is measured in hertz.

SummarySummary

Periodic Pulse Waveforms

Tf

1

fT

1

The clock is a basic timing signal that is an example of a periodic wave.

What is the period of a repetitive wave if f = 3.2 GHz?

GHz 2.3

11

fT 313 ps


SummarySummary

Pulse Definitions

In addition to frequency and period, repetitive pulse waveforms are described by the amplitude (A), pulse width (tW) and duty cycle. Duty cycle is the ratio of tW to T.

Volts

Time

Amplitude (A)

Pulse width (tW)

Period, T


A timing diagram is used to show the relationship between two or more digital waveforms,

SummarySummary

Timing Diagrams

Clock

A

B

C

A diagram like this can be observed directly on a logic analyzer.


Data can be transmitted by either serial transfer or parallel transfer.

SummarySummary

Serial and Parallel Data

Computer Modem

1 0 1 1 0 0 1 0

t0 t1 t2 t3 t4 t5 t6 t7

Computer Printer

0

t0 t1

1

0

0

1

1

0

1


SummarySummary

Basic Logic Functions

True only if all input conditions are true.

True only if one or more input conditions are true.

Indicates the opposite condition.


SummarySummary

Basic System Functions

And, or, and not elements can be combined to form various logic functions. A few examples are:

The comparison function

Basic arithmetic functionsAdder

Twobinarynumbers Carry out

A

BCout

CinCarry in

SumΣ

Twobinarynumbers

Outputs

A

BA < B

A = B

A > BComparator


SummarySummary


The encoding function

The decoding functionDecoder

Binary input

7-segment display

Encoder9

8 9

4 5 6

1 2 3

0 . +/–

7

Calculator keypad

876543210

HIGH

Binary codefor 9 used forstorage and/orcomputation


SummarySummary


The data selection function

MultiplexerA

Switchingsequence

control input

B

C

∆t2

∆t3

∆t1

∆t2

∆t3

∆t1

DemultiplexerD

E

F

Data from A to D

Data fromB to E

Data fromC to F

Data fromA to D

∆t1 ∆t2 ∆t3 ∆t1

Switchingsequence

control input


SummarySummary


The counting function

…and other functions such as code conversion and storage.

Input pulses

1

Counter Parallel output lines Binary

code for 1

Binary code for 2

Binary code for 3

Binary code for 4

Binary code for 5

Sequence of binary codes that represent the number of input pulses counted.

2 3 4 5


SummarySummary


One type of storage function is the shift register, that moves and stores data each time it is clocked.

0 0 0 00101Initially, the register contains only invaliddata or all zeros as shown here.

1 0 0 0010First bit (1) is shifted serially into theregister.

0 1 0 001Second bit (0) is shifted serially intoregister and first bit is shifted right.

1 0 1 00Third bit (1) is shifted into register andthe first and second bits are shifted right.

0 1 0 1Fourth bit (0) is shifted into register andthe first, second, and third bits are shiftedright. The register now stores all four bitsand is full.

Serial bitson input line


SummarySummary

Integrated Circuits

Plasticcase

Pins

Chip

Cutaway view of DIP (Dual-In-line Pins) chip:

The TTL series, available as DIPs are popular for laboratory experiments with logic.


SummarySummary

An example of laboratory prototyping is shown. The circuit is wired using DIP chips and tested.

Integrated Circuits

In this case, testing can be done by a computer connected to the system.

DIP chips


SummarySummary

Integrated Circuits

DIP chips and surface mount chips

Pin 1

Dual in-line package Small outline IC (SOIC)


SummarySummary

Integrated Circuits

Other surface mount packages:

SOIC PLCC LCCC

End viewEnd viewEnd view


SummarySummary

Test and Measurement Instruments

H O R I Z O N TA LV E R T I C A L T R IG G E R

5 s 5 n s

P O S IT I O N

C H 1 C H 2 E X T TR IG

A C - D C - G N D

5 V 2 m V

V O L T S / D IV

C O U P L IN G

C H 1 C H 2 B O T H

P O S IT I O N

A C - D C - G N D

5 V 2 m V

V O L T S / D IV

C O U P L IN G

S E C / D IV

P O S IT I O N

S L O P E

Ð +

L E V E L

S O U R C E

C H 1

C H 2

E X T

L IN E

T R IG C O U P

D C A C

D IS P L A Y

IN T E N S IT Y

P R O B E C O M P5 V

The front panel controls for a general-purpose oscilloscope can be divided into four major groups.


SummarySummary

Test and Measurement InstrumentsC h 1

E x t e rn a lt r ig g e r

C o n v e r s io n / s t o ra g e( D ig i t a l s c o p e s o n ly )

S ig n a l c o u p lin g

A CD C G N D A m p

C h 2 C o n v e r s io n / s t o ra g e( D ig i t a l s c o p e s o n ly )

A CD C G N D A m p

V o l t s / D i v

V e r t i c a lp o s i t i o n

A CD C

E x t

T r ig g e rs o u r c e

E x t e r n a l t r ig g e rc o u p l in g

C h 1C h 2

L in e

T r ig g e rc i r c u it s

T r ig g e rl e v e l a n ds lo p e

T im e b a s e

S e c / D iv

H o r iz o n t a lp o s i t io n

C o n t r o l a n d p r o c e s s( D ig i t a l s c o p e s o n ly )

In t e n s i t y

A C

D C t o a l l s e c t io n sP o w e r s u p p ly

V e r t i c a l s e c t i o n

D i s p l a y s e c t i o n

H o r i z o n t a l s e c t i o nT r i g g e r s e c t i o n

D ig i t a lo n ly

A n a lo go n ly

For measuring digital signals, use DC coupling

Normally, trigger on the slower of two waveforms when comparing signals.


SummarySummary


The logic analyzer can display multiple channels of digital information or show data in tabular form.


SummarySummary


V

1 s

1 s

4 0 m A

1 0 A

C O M

R a n g eA u t o ra n g e

To u c h / H o ld

F u s e d

O F F V

V

H z

m V

A

0.01 V

The DMM can make three basic electrical measurements.

Voltage

Resistance

Current

In digital work, DMMs are useful for checking power supply voltages, verifying resistors, testing continuity, and occasionally making other measurements.


SummarySummary

Programmable Logic

Programmable logic devices (PLDs) are an alternative to fixed function devices. The logic can be programmed for a specific purpose. In general, they cost less and use less board space that fixed function devices.

Fixed ORarray and

output logic

ProgrammableAND array

A PAL device is a form of PLD that uses a combination of a programmable AND array and a fixed OR array:


Selected Key TermsSelected Key Terms

Analog

Digital

Binary

Bit

Pulse

Being continuous or having continuous values.

Related to digits or discrete quantities; having a set of discrete values.

Having two values or states; describes a number system that has a base of two and utilizes 1 and 0 as its digits.

A binary digit, which can be a 1 or a 0.

A sudden change from one level to another, followed after a time, called the pulse width, by a sudden change back to the original level.



Clock

Gate

NOT

AND

OR

A basic timing signal in a digital system; a periodic waveform used to synchronize actions.

A logic circuit that performs a basic logic operations such as AND or OR.

A basic logic function that performs inversion.

A basic logic operation in which a true (HIGH) output occurs only when all input conditions are true (HIGH).

A basic logic operation in which a true (HIGH) output occurs when when one or more of the input conditions are true (HIGH).



Fixedfunction logic

Programmable logic

A category of digital integrated circuits having functions that cannot be altered.

A category of digital integrated circuits capable of being programmed to perform specified functions.


1. Compared to analog systems, digital systems

a. are less prone to noise

b. can represent an infinite number of values

c. can handle much higher power

d. all of the above



2. The number of values that can be assigned to a bit are

a. one

b. two

c. three

d. ten



3. The time measurement between the 50% point on the leading edge of a pulse to the 50% point on the trailing edge of the pulse is called the

a. rise time

b. fall time

c. period

d. pulse width



4. The time measurement between the 90% point on the trailing edge of a pulse to the 10% point on the trailing edge of the pulse is called the

a. rise time

b. fall time

c. period

d. pulse width



5. The reciprocal of the frequency of a clock signal is the

a. rise time

b. fall time

c. period

d. pulse width



6. If the period of a clock signal is 500 ps, the frequency is

a. 20 MHz

b. 200 MHz

c. 2 GHz

d. 20 GHz



7. AND, OR, and NOT gates can be used to form

a. storage devices

b. comparators

c. data selectors

d. all of the above



8. A shift register is an example of a

a. storage device

b. comparator

c. data selector

d. counter



9. A device that is used to switch one of several input lines to a single output line is called a

a. comparator

b. decoder

c. counter

d. multiplexer



10. For most digital work, an oscilloscope should be coupled to the signal using

a. ac coupling

b. dc coupling

c. GND coupling

d. none of the above



Answers:

1. a

2. b

3. d

4. b

5. c

6. c

7. d

8. a

9. d

10. b

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