Introduction of digital system

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 OutcomesAt the end of this chapter, you must be able to– Distinguish between analog & digital

representations– State the advantages and disadvantages of

digital techniques 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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1.1 Numerical Representations

Most naturally occurring physical quantities in our world are analog in nature.

Quantities are measured, monitored, recorded, manipulated arithmetically, observed in most physical systems.

Important when dealing with quantities – To represent their values efficiently and accurately– 2 ways to represent them:

1) ANALOG representation

2) DIGITAL representation

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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 values

Example– 1) Speedometer– 2) Thermometer

⇒ In electrical mean, the measured/processed physical quantity is converted to a 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 logical information or physical quantities that are represented in digital form.

Example: digital calculator

ANALOG SYSTEM

Devices that manipulate physical quantities that are represented in analog form.

Example: magnetic tape recording and playback equipment

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Example 1: TapeDuring playback, a magnetic material in the tape head is magnetized as the magnetic tape passes.

Then, the magnetic field penetrates a coil of wire which is wrapped around it.

Change in magnetic field will induce a voltage in the coil. This induced voltage forms an electrical image of the signal which 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 and efficiently

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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 system

4. 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 analogue circuits & produce more heat

5. Digital circuits are made from analogue components – must make sure the digital behaviour is not affected by the analogue

6. Digital circuits are sometimes more expensive (in small quantity)

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1.5 Digital Systems Overcome the Drawback of Analog Systems

When dealing with analogue inputs and outputs, four steps must be followed1. Convert the physical variable to an electrical

signal (analogue)

2. Convert the electrical (analogue) signal into digital form ⇒ ADC (Analogue Digital Converter)

3. Process (operate on) the digital information

4. Convert the digital outputs back to real-world analogue 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 digital technology.– Decimal ⇒ most familiar to us– Binary– Octal– Hexadecimal

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Decimal SystemIt 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 is the LSD.

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Binary SystemIt is also called as base 2 (due to 2-symbols representation)It is also a positional numeral system. However, the weight 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 21

bit 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 is presented in binary form.Binary quantities can be represented by any device that 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 digital system is the transmission of information from one place to another.

The transmitted information is represented as voltages at the outputs of a sending circuit that are connected to the inputs of a receiving circuit.

2 basic methods for digital information transmission:– Parallel (faster in terms of speed)– Serial (simpler in terms of circuit design)

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Parallel Transmission

The bits presenting the information (code) are sent simultaneously

⇒ faster speed, however it requires more signal lines (complexity)

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Serial Transmission

The bits presenting the information (code) are sent one bit at a time using a single transmission line until all bits are transmitted.

⇒ slower speed, but it requires only 1 signal line

The data transmitted could start from either MSB or LSB (depending on a system)

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1.9 Memory & Memoryless Circuits

MEMORY CIRCUIT– Memory indicates the system has the means to

store information 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

memory because 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

instruction to 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 instruction

instructed.

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Types of computersMicroprocessor, µP – CPU in an integrated circuit

Microcomputer– Computer that use a µP to perform a wide range

of applications depending on the software– Performs general tasks

Microcontroller– Computer that use a µP to perform limited

task(s)– Have all the elements of a complete computer

(CPU, memory & I/O ports) in one integrated circuit.