chap1 intro digital system

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
http://en.wikipedia.org/wiki/Image:153056995_5ef8b01016_o.jpg


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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

chap1 intro digital system

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