TNTRODUCTO RYCONCEPTS
NUMERICAL REPRESENTATIONS
There are basically two ways of representing the numerical
value of quantities: analog and digital.
Analog Representations
In analog representation a quantity is represented by a
continuously variable, proportional indicator.
Analog quantities have añ important characteristic, no matter
howthey are represented: they can vary Over a continuous
range of valves.
Thermometers before the digital revolution used analog
representation to measure temperature, and many are still in
use today.
In these two examples the physical quantities (speed and
temperature) are being coupled to an indicator by purely
mechanical means. In electricalanalog systems, the physical
quantity that is being measured or processed is converted
to a proportional voltage or current (electrical signal). This
voltage or current isthen used by the system for display,
processing, or control purposes
DIgital RepresentatIons
In digital representation the quantities are represented not
by continuously variable indicators but by symbols called
digits. As an example, consider the digital clock, which
provides the time of day in the form of decimal digits that
represent hours andminutes (and sometimes seconds) The
major difference between analog and digital quantities, then,
can be simply stated as follows:
analog = continuous
digital =discrete (step by step) 1
HDMI 1
1024 x 768 @60Hz
FRAME LOCK
Thermometers before the digital revolution used analog
representation to measure temperature, and many are still in
use today.
In these two examples the physicalquantities (speed and
temperature) are being coupled to an indicator by purely
mechanical means. In electrical analog systems, the physical
quantity that is being measured or processed is converted
to a proportional voltage or current (electrical signal). This
voltage or current is then used by thesystem for display,
processing, or control purposes
DIGIIAL AIND AINALOG SYSTEIMS
Adigital system is a combination of devices designed to
manipulate logical information or physical quantities that are
represented in digital form; that is, the quantities can take on
only discrete values. These devices are most often electronics,
but they can also be mechanical, magnetic or pneumatic.
An analogsystem contains devices that manipulate physical
quantities that represented in analog form.
Advantages of DigitalTechniques
1. Digital systems are generally easier to design.
2. Information storage is easy.
3. Accuracy and precision are easier to maintain throughout the system.
4. Operation can be programmed.
5. Digital circuits are less affected by noise.
6. More digital circuitry can be fabricated on IC chips.
LmitaIons or DIgita Techniques
There are really very few drawbacks when using
digital techniques. The two biggest problems are:
The real world is analog.
Processing digitized signals takes time.
digital techniques when dealing with analog inputs and outputs,
foursteps must be followed:
1. Convert the physical variable to an electrical signal (analog).
2. Convert the electrical (analog)signal into digital form.
3. Process (operate on) the digital information.
4.Convert the digital outputs back to real-world analog form.
A temperature sensor in the heated space converts the measured
temperature to a proportional voltage. This analog voltage is
converted to a digital quantity by an analog-to-digital converter
(ADC). This value is thencompared tothe desired value and used
to determine a digital value of how much heat is needed. The
digital value is converted to an analog quantity (voltage) by a
digital-to-analog converter (DAC). This voltage is applied to a
heating element, which _will produce heat that is related to the
voltage applied and will affect the temperature of the space.
Digital input:
Set Desired Temperature Digital signal representing
power (voltage) to heater
Temperature controlled
Digital Processor Digital-Analog space
Conversion
Sensor
Heat
Analog-Digital
Conversion
Digital signal representing Analog signal representing
actual temperature actual temperature
FIGURE 1-1 Blbck diagram of aprecision digital temperature control system.
Oeween analOg and dlgItal takes place Is In the recording oT
COnverSTON
tapes because they
audio. Compact disks (CDs) have replaced cassette
playing back music. The
provide amuch better means for recording and
process works something like this:
analog
(1) sounds from instruments and human voices produce an
voltage signal in a microphone;
to
(2)this analog signal is converted to adigital format using an analog
digital conversion process;
(3) the digital information is stored on the CD's surface:
(4) duringplayback, the CD player takes the digital information
from the CDsurface and converts it into an analog signal that is then
amplified and fed to aspeaker, where it can be picked up by the human
ear.
PARALLEL AND SERIAL TRANSMISSION
the two basic methods for digital information transmission: parallel and serial
"H" "
MSB
LSB
(a)
(a) Parallel transmissionuses one connecting line per bit,and all bitsare transmitted
simultaneously;
"H"
00010010 10010110
SS
LSB MSB LSB MSB
(b)
hthis scenario, assume we are trying to print the word "Hi" on the printer. The
binary code for "H" is 01001000 and the binary code for "i" is 01101001. Each
character (the "H" and the "")are made up of eight bits. Using parallel
transmission, alleight bitsare sent simultaneously over eight wires.The "H"
issent first, followed by the "i."
Deciiar Countng
When counting in the decimal system, we start with 0 in the units
position andtake each symbol (digit) in progression until we reach 9.
Then we add a1 to the next higher position and start over with Oin the
first position This process continues until the count of 99 is reached.
Then we
add a 1 tothe third position and start over with Os in the first two
positions. The same pattern is followed continuously as high as we wish
to côunt.
eight bits?
What s the largest number that can be represented using
Solution
2N-1 =28-1 = 25510 = 11111111
What is the decimal equivalent of 1101011,?
Tming DIagrams
Atiming diagram is the graphical representation of input and
output signals as functions of time. Since the inputs and
outputs can only take the values 0 or 1, their graphical
representations are series of square pulses with a variety of
time lengths.
MEMORY
When an input is applied to such a circuit, the output will change
its state, but it will remain in the new state even after the input is
removed. This property of retaining its response to a momentary
input is called memory.
DIGITAL COMPUTERS
acomputer is asystem of hardware that performs arithmetic
operations, manipulates data (usuallyin binary form), and makes decisions.
Major Parts of a Computer
Central Processing
Unit (CPU)
Arithmetic/
logic
Data, Input Control Data,
information Output
information
Control signals
Memory Data or information
FIGURE 1/12 Functional diagram of a digital computer.
