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8/3/2019 Chap1 Intro Digital System
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CHAPTER 1
INTRODUCTION TO DIGIT
1.1 Numerical Representation
1.2 Digital & Analog Systems
1.3 Advantages of Digital Techniques
1.4 Disadvantages of Digital Techniques
1.5 Digital Systems Overcome the Drawback of Analog Systems
1.6 Digital Number Systems
1.7 Representing Binary Quantities
1.8 Digital Data Transmission
1.9 Memory & Non-Memory Circuits
1.10 Digital Computers
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Learning Outcomes
At the end of this chapter, you must be able to
Distinguish between analog & digital representations
State the advantages and disadvantages of digitaltechniques compared with analog
Understand the need for ADCs and DACs State the differences between parallel and serial
transmissions
Describe the property of memory
Describe the major parts of a digital computer &understand their functions
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Analog Representation
Represent a quantity by a continuously variable,proportional indicator
Characteristic of analog quantities
They can vary over a continuous range of valuesExample
1) Speedometer
2) Thermometer
In electrical mean, the measured/processed physical quantity is converted toa proportional electrical signal (V or I) used by the system for display,processing or control purposes
Use a mechanical
means
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Digital Representation
Represent a quantity by a symbol, called digits.
Characteristic of digital quantities
They are varied in discrete steps
Example 1) Digital Clock
2) Digital weighting scale
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1.2 Digital & Analog Systems
DIGITAL SYSTEM
Combination of devices designed to manipulate logicalinformation or physical quantities that are representedin digital form.
Example: digital calculator
ANALOG SYSTEM
Devices that manipulate physical quantities that arerepresented in analog form.
Example: magnetic tape recording and playbackequipment
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Example 1: Tape
During playback, a magnetic material inthe tape head is magnetized as themagnetic tape passes.
Then, the magnetic field penetrates a coilof wire which is wrapped around it.
Change in magnetic field will induce avoltage in the coil. This induced voltageforms an electrical image of the signalwhich is recorded on the tape.
Source: http://hyperphysics.phy-astr.gsu.edu/HBASE/Audio/tape.html#c4
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Example 2: Computer
All the stored and processed data are in binary form.Why ?
Digital circuits/devices only concerns about two operating states/logic levels, This system allows computers to perform complex calculations very quickly andefficiently
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Example 3: CD
CD player: digital and analog parts co-exist together(source:
How Stuff Works website)
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1.3 Advantages of Digital Techniques
1. Digital systems are easier to design
2. Information storage is easy
3. Accuracy & precision are easier to maintain
throughout the system4. Operation can be programmed
5. Digital circuits are less affected by noise
6. Digital circuitry can be fabricated on IC chips
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1.4 Disadvantages of Digital Techniques
1. The real world is analogue
2. Digital systems can be fragile
3. Processing digitised signals takes time
4. Digital circuits use more energy than analoguecircuits & produce more heat
5. Digital circuits are made from analogue components must make sure the digital behaviour is not affected
by the analogue6. Digital circuits are sometimes more expensive (in
small quantity)
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1.5 Digital Systems Overcome theDrawback of Analog Systems
When dealing with analogue inputs and outputs, foursteps must be followed
1. Convert the physical variable to an electrical signal(analogue)
2. Convert the electrical (analogue) signal into digitalform ADC (Analogue Digital Converter)
3. Process (operate on) the digital information
4. Convert the digital outputs back to real-worldanalogue form DAC (Digital Analogue Converter)
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DIGITAL
Example: Block diagram for a digital temperature control system
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1.6 Digital Number Systems
There are many numbering systems used in digitaltechnology.
Decimal most familiar to us
Binary
Octal
Hexadecimal
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Decimal System
It is also called as base 10 (due to 10-symbols representation)It is a positional numeral system.
Example:
Given a decimal number of 1429
For digit 1 one thousand (1 x 103)
digit 4 four hundred (4 x 102)digit 2 twenty (2 x 101)
digit 9 nine (9 x 100)
What is the MSD (most significant digit, first nonzero digit from the left)of 1429?
What is the LSD (least significant digit, last nonzero digit from the right)of 1429?
For a whole number, the first digit to the left of the radix point isthe LSD.
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Binary System
It is also called as base 2 (due to 2-symbolsrepresentation)
It is also a positional numeral system. However, theweight of its bit is different than decimal.
Example: Given a binary number of 1011
For bit 1 1 x 23
bit 0 0 x 22
bit 1 1 x 21bit 1 1 x 20
What is the MSB of 1011?
What is the LSB of 1011?
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1.7 Representing Binary Quantities
The information being processed in digital systems ispresented in binaryform.
Binary quantities can be represented by any devicethat has only two operating states or possible
conditionsExample:
A switch has only 2 states open or closed
Information stored in CD holes are burnt form pits
(non-reflective) as 1 or reflective areas as 0 Diode conducting or non-conducting
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Example: Using voltage level to represent the binary values
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1.8 Digital Data Transmission
The most common operations that occur in any digitalsystem is the transmission of information from oneplace to another.
The transmitted information is represented as voltagesat the outputs of a sending circuit that are connectedto the inputs of a receiving circuit.
2 basic methods for digital information transmission:
Parallel (fasterin terms of speed)
Serial (simplerin terms of circuit design)
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Parallel Transmission
The bits presenting the information (code) are sentsimultaneously
faster speed, however it requires more signal lines(complexity)
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Serial Transmission
The bits presenting the information (code) are sentone bit at a time using a single transmission line untilall bits are transmitted.
slower speed, but it requires only 1 signal line
The data transmitted could start from either MSB orLSB (depending on a system)
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1.9 Memory & Memoryless Circuits
MEMORY CIRCUIT
Memory indicates the system has the means to storeinformation about the input from the past.
Example: Flip-flop
When an input is applied to the circuit, the output will change its state, but it will
remain in the new state even when the input is removed.
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MEMORYLESS CIRCUIT
The circuit does not exhibit the property of memorybecause the output reverts back to its normal state.
When an input is applied to the circuit, the output will change its state, and it will
return back to its original state when the input is removed.
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1.10 Digital Computers
Functional diagram of a digital computer
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There are 5 major functional parts:
Arithmetic/logic unit (ALU) Performs all arithmetic calculations and logical decisions
Sends the results to memory unit for storage
Memory unit Stores the instructions & data from input
Stores the results of arithmetic operation from ALU
Supplies information to output
RAM (Random Access Memory) & ROM (Read-Only Memory)
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Output unit Takes data from the memory unit and prints out, display , etc i.e. to
the external
Input unit Instruction set and data are fed through this
Control unit Takes and interprets instructions from input
Sends related signals to other units to cause the specific instructionto be executed
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Central Processing Unit (CPU)
Combination of CONTROL unit & ALU
Function:
Fetch and interpret instruction
Control and perform the operation as instructioninstructed.
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Types of computers
Microprocessor, P CPU in an integrated circuit
Microcomputer Computer that use a P to perform a wide range of
applications depending on the software
Performs general tasks
Microcontroller Computer that use a P to perform limited task(s)
Have all the elements of a complete computer (CPU,memory & I/O ports) in one integrated circuit.
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Informations
Quiz 1 that cover chapter 3, on 22/9/2011, Thursday.
Prepare the answers for tutorial in the module (chapter3 and 1), that will be discussed on Thursday.
Module will be distributed today, check email