Chapter 1 floyd

© 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

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

ed
SummarySummary
Digital Computer

ed
SummarySummary
Hierarchy of Digital Systems

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Digital electronics uses circuits that have two states HIGH
and LOW, which are represented by two different voltage
levels called Logic Levels. 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 0 or 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 consist of voltage levels that are changing
back and forth between HIGH and LOW levels or states.
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 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.
SummarySummary
Pulse Definitions
90%
50%
10%
Baseline
Pulsewidth
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.
SummarySummary
Periodic Pulse Waveforms
T
f
1
=
f
T
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?
===
GHz2.3
11
f
T 313 ps
Waveforms are classified as Periodic & Non-Periodic

ed
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.
Duty Cycle = (tw / T) 100%
Volts
Time
Amplitude (A)
Pulse
width
(tW)
Period, T

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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.

ed
Data can be transmitted by either serial transfer e.g USB or
parallel transfer e.g Data Bus in a computer.
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

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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.

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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 functions Adder
Two
binary
numbers Carry out
A
B
Cout
CinCarry in
SumΣ
Two
binary
numbers
Outputs
A
B
A< B
A= B
A> B
Comparator

ed
SummarySummary
The encoding function
The decoding function
Decoder
Binary input
7-segment display
Encoder9
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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SummarySummary
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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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

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SummarySummary
One type of storage function is the shift register,
that moves and stores data each time it is clocked.
0 0 0 00101
Initially, theregister contains onlyinvalid
data or all zeros as shown here.
1 0 0 0010
First bit (1) is shifted serially into the
register.
0 1 0 001
Second bit (0) is shifted serially into
register and first bit is shifted right.
1 0 1 00
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 areshifted
right.The register now stores all four bits
and is full.
Serial bits
on input line

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SummarySummary
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.

Chapter 1 floyd

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