Topic01 - Introductory Concepts of Digital

© 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved
Floyd, Digital Fundamentals, 10th
ed
Digital Logic Design
Introductory Concepts
© 2009 Pearson Education
Chapter 1

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Most natural quantities that we see are analog and vary
continuously.
Summary
Summary
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 12
P.M.
Temperature
(°F)
70
Time of day

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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.
Summary
Summary
Analog and Digital Systems
Digital data
CD drive
10110011101
Analog
reproduction
of music audio
signal
Speaker
Sound
waves
Digital-to-analog
converter
Linear amplifier

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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.
Summary
Summary
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

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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.
Summary
Summary
Digital Waveforms
Falling or
leading edge
(b) Negative–going pulse
HIGH
Rising or
trailing edge
LOW
(a) Positive–going pulse
HIGH
Rising or
leading edge
Falling or
trailing edge
LOW
t0
t1
t0
t1

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Actual pulses are not ideal but are described by the rise time,
fall time, amplitude, and other characteristics.
Summary
Summary
Pulse Definitions
90%
50%
10%
Base line
Pulse width
Rise time Fall time
Amplitude tW
tr tf
Undershoot
Ringing
Overshoot
Ringing
Droop

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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.
Summary
Summary
Periodic Pulse Waveforms
T
f
1

f
T
1

What is the period of a repetitive wave if f = 3.2 GHz?



GHz
2
.
3
1
1
f
T 313 ps

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Summary
Summary
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 portion of a periodic digital waveform is shown in below
Figure . The measurements are in milliseconds. Determine the
following:
• (a) period (b) frequency (c) duty cycle

The Clock
Example of a clock waveform synchronized with a waveform representationof a
sequence of bits.

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A timing diagram is used to show the relationship between
two or more digital waveforms,
Summary
Summary
Timing Diagrams
Clock
A
B
C

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

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Summary
Summary
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.

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Summary
Summary
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 functions Adder
Two
binary
numbers Carry out
A
B
Cout
Cin
Carry in
Sum
Σ
Two
binary
numbers
Outputs
A
B
A< B
A= B
A> B
Comparator

ed
Summary
Summary
The encoding function
The decoding function
Decoder
Binary input
7-segment display
Encoder
9
8 9
4 5 6
1 2 3
0 . +/–
7
Calculator keypad
8
7
6
5
4
3
2
1
0
HIGH
Binary code
for 9 used for
storage and/or
computation

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Summary
Summary
The data selection function
Multiplexer
A
Switching
sequence
control input
B
C
∆t2
∆t3
∆t1
∆t2
∆t3
∆t1
Demultiplexer
D
E
F
Data from
Ato D
Data from
Bto E
Data from
Cto F
Data from
Ato D
∆t1 ∆t2 ∆t3 ∆t1
Switching
sequence
control input

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Summary
Summary
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

ed
Summary
Summary
One type of storage function is the shift register,
that moves and stores data each time it is clocked.
0 0 0 0
0101
Initially
, the register contains onlyinvalid
data or all zeros as shown here.
1 0 0 0
010
First bit (1) is shifted serially into the
register.
0 1 0 0
01
Second bit (0) is shifted serially into
register and first bit is shifted right.
1 0 1 0
0
Third bit (1) is shifted into register and
the first and second bits are shifted right.
0 1 0 1
Fourth bit (0) is shifted into register and
the first, second,and third bits are shifted
right.The register now stores all four bits
and is full.
Serial bits
on input line

ed
Summary
Summary
Integrated Circuits
Plastic
case
Pins
Chip
Cutaway view of DIP (Dual-In-line Pins) chip:
The TTL series, available as DIPs are popular
for laboratory experiments with logic.

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Summary
Summary
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

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Summary
Summary
Integrated Circuits
DIP chips and surface mount chips
Pin 1
Dual in-line package Small outline IC (SOIC)

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Summary
Summary
Integrated Circuits
Other surface mount packages:
SOIC PLCC LCCC
End view
End view
End view

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Summary
Summary
Test and Measurement Instruments
HORIZO NTAL
VERTIC AL TRIG G ER
5 s 5 ns
POSITION
C H 1 C H 2 EXT TRIG
AC -DC -GND
5V 2 mV
VOLTS/DIV
C OUPLING
C H 1 C H 2 BOTH
POSITION
AC -DC -GND
5 V 2 mV
VOLTS/DIV
C OUPLING
SEC /DIV
POSITION
SLOPE
Ð +
LEVEL
SOURC E
C H 1
C H 2
EXT
LINE
TRIG C O UP
DC AC
DISPLAY
INTENSITY
PROBE C OMP
5 V
The front panel controls for a general-purpose oscilloscope
can be divided into four major groups.

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

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Summary
Summary
V
1 s
1 s
40 m A
10 A
C O M
Ra nge
Autora nge
Touc h/Hold
Fused
O FF V
V
Hz
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.

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Summary
Summary
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 OR
array and
output logic
Programmable
AND 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 Terms
Selected 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.

Selected Key Terms
Selected Key Terms
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).

Selected Key Terms
Selected Key Terms
Fixed-function
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

Topic01 - Introductory Concepts of Digital

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