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Digital
Fundamentals
Tenth Edition
Floyd
Chapter 1
Floyd, Digital Fundamentals, 10th ed
© 2008 Pearson Education
Slide 1
Summary
Analog Quantities
Most natural quantities that we see are analog and vary
continuously. Analog systems can generally handle higher
power than digital systems.
Temperature
(°F)
100
95
90
85
80
75
70
Time of day
1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12
A .M .
P.M .
Digital systems can process, store, and transmit data more
efficiently but can only assign discrete values to each point.
Floyd, Digital Fundamentals, 10th ed
Slide 2
Summary
Analog and Digital Systems
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.
CD drive
10110011101
Digital data
Digital-to-analog
converter
Linear amplifier
Analog
reproduction
of music audio
signal
Speaker
Sound
waves
Floyd, Digital Fundamentals, 10th ed
Slide 3
Summary
Binary Digits and Logic Levels
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.
VH(max)
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
VH(min)
Invalid
VL(max)
LOW
VL(min)
Floyd, Digital Fundamentals, 10th ed
Slide 4
Summary
Digital Waveforms
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.
HIGH
HIGH
Rising or
leading edge
LOW
Falling or
trailing edge
t0
(a) Positive–going pulse
Floyd, Digital Fundamentals, 10th ed
t1
Falling or
leading edge
LOW
Rising or
trailing edge
t0
t1
(b) Negative–going pulse
Slide 5
Summary
Pulse Definitions
Actual pulses are not ideal but are described by the rise time,
fall time, amplitude, and other characteristics.
Overshoot
Ringing
Droop
90%
Amplitude
tW
50%
Pulse width
10%
Ringing
Base line
Floyd, Digital Fundamentals, 10th ed
Undershoot
tr
tf
Rise time
Fall time
Slide 6
Summary
Periodic Pulse Waveforms
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.
1
f 
T
1
T
f
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?
T
Floyd, Digital Fundamentals, 10th ed
1
1

 313 ps
f 3.2 GHz
Slide 7
Summary
 8 bits = 1 byte
 1024 Bytes = 1 KB (kilobyte)
 1024 Kilobytes = 1 MB (megabyte)
 1024 Megabytes = 1 GB (gigabyte)
 1024 Gigabytes = 1 TB (Terabyte)
103 Hz =1 kHz (kilohertz)
106 Hz =1 MHz (megahertz)
109 Hz =1 GHz (gigahertz)
1012 Hz =1 THz (terahertz)
A picosecond is 10−12 of a second
10−3 s =1 ms (millisecond)
103 s =1 ks (kilosecond)
10−6 s=1 µs (microsecond)
106 s =1 Ms (megasecond)
 10−9 s=1 ns (nanosecond)
109 s =1 Gs (gigasecond)
10−12 s=1 ps (picosecond)
 1012 s =1Ts (terasecond)
Floyd, Digital Fundamentals, 10th ed
Slide 8
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
Amplitude (A)
Pulse
width
(tW)
Time
Period, T
Floyd, Digital Fundamentals, 10th ed
Slide 9
Summary
Timing Diagrams
A timing diagram is used to show the relationship between
two or more digital waveforms,
Clock
A
B
C
Floyd, Digital Fundamentals, 10th ed
Slide 10
Summary
Serial and Parallel Data
Data can be transmitted by either serial transfer or parallel
transfer.
1
t0
0
t1
1
t2
1
t3
0
0
t 4 t 5 t6
1
0
t7
Computer
Modem
1
Computer
Printer
0
1
1
0
0
1
0
t0
Floyd, Digital Fundamentals, 10th ed
t1
Slide 11
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.
Floyd, Digital Fundamentals, 10th ed
Slide 12
Summary
Basic System Functions
And, or, and not elements can be combined to form
various logic functions. A few examples are:
The comparison function
A
Comparator
A> B
Two
binary
numbers
A= B
B
A< B
Basic arithmetic functions
Adder
A
Two
binary
numbers
B
Carry in
Floyd, Digital Fundamentals, 10th ed
Outputs
Σ
Cout
Sum
Carry out
Cin
Slide 13
Summary
Basic System Functions
HIGH
The encoding function
7
4
8
1
2
3
0
.
+/–
5
9
6
9
8
7
6
5
4
3
2
1
0
Encoder
Binary code
for 9 used for
storage and/or
computation
Calculator keypad
The decoding function
Decoder
Binary input
7-segment display
Floyd, Digital Fundamentals, 10th ed
Slide 14
Summary
Basic System Functions
The data selection function
Multiplexer
A
∆t1
B
Demultiplexer
Data from
A to D
Data from
B to E
Data from
C to F
Data from
A to D
∆ t1
∆ t2
∆ t3
∆t 1
D
∆t1
E
∆t2
C
Floyd, Digital Fundamentals, 10th ed
∆t2
∆t3
∆t3
Switching
sequence
control input
Switching
sequence
control input
F
Slide 15
Summary
Basic System Functions
The counting function
Counter
1
2
3
4
Input pulses
5
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.
…and other functions such as code conversion
and storage.
Floyd, Digital Fundamentals, 10th ed
Slide 16
Summary
Basic System Functions
One type of storage function is the shift register,
that moves and stores data each time it is clocked.
Serial bits
on input line
0101
010
01
0
0 0 0 0
1 0 0 0
0 1 0 0
1 0 1 0
0 1 0 1
Floyd, Digital Fundamentals, 10th ed
Initially, the register contains onlyinvalid
data or all zeros as shown here.
First bit (1) is shifted serially into the
register.
Second bit (0) is shifted serially into
register and first bit is shifted right.
Third bit (1) is shifted into register and
the first and second bits are shifted right.
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.
Slide 17
Summary
Integrated Circuits
Cutaway view of DIP (Dual-In-line Pins) chip:
Chip
Plastic
case
Pins
The TTL series, available as DIPs are popular
for laboratory experiments with logic.
Floyd, Digital Fundamentals, 10th ed
Slide 18
Summary
Integrated Circuits
An example of laboratory prototyping is shown. The circuit
is wired using DIP chips and tested.
DIP chips
In this case, testing can
be done by a computer
connected to the system.
Floyd, Digital Fundamentals, 10th ed
Slide 19
Summary
Integrated Circuits
DIP chips and surface mount chips
Pin 1
Dual in-line package
Floyd, Digital Fundamentals, 10th ed
Small outline IC (SOIC)
Slide 20