A Summer Training Report On

Embedded system & Interfacing with ATmega8

In partial fulfillment of the degree of

Bachelor of Technology

In

Electronics And Communication Engineering

Submitted To: Submitted By:

Ms.Pushpa Gothwal Shivangi Dwivedi

Department Of Electronics B.Tech - ECE,

7th sem

Amity School of Engineering & Technology

Amity University Rajasthan

DECLARATION

I do, hereby, declare that the industrial training report entitled “ Embedded system & interfacing with

ATmega8” is an authentic work developed by me at “Skyphi technologies,jaipur(rajasthan)” under the

guidance of Mr.Rahul Agrawal and submitted as 7th

semester training work for the degree of B.Tech. ECE

at Amity School of Engineering & Technology, Amity University Rajasthan, Jaipur.

I also declare that, any or all contents incorporated in this report have not been submitted in any form for the

award of any degree or diploma of any other institution or university.

shivangi dwivedi

A20405111238

ASET, AUR

CONTENTS

Acknowledgement (iii)

Abstract (ix)

List Of Figures

1.Embedded Systems

1.1 Introduction 1

1.2Examples of embedded system 1

1.3 Characteristics of Embedded System 3

1.4 CATEGORIES OF EMBEDDED SYSTEMS 3

1.5 Application Areas of Embedded Systems 5

1.6 Overview of embedded systems architecture 6

1.7 Specialties of an Embedded Systems 8

1.8 Microprocessor (MPU) 9

1.9 Microcontroller (MCU) 9

1.10 Comparision Between Microprocessor And Microcontroller 10

1.11 Types of Microcontroller 11

2.8051 Microcontroller

2.1About 8051 12

2.2 Block diagram 12

2.3 Typical applications 13

2.4 Pinout Description 14

2.5 Programming Model Of 8051 16

2.6 Accumulator 16

2.7 B Register 17

2.8 PSW (Program Status Word) Register 17

2.9 Data Pointer Register (DPTR) 19

2.10 Stack Pointer (SP) Register 19

2.11 Internal memory 20

2.11.1 Internal RAM 20

2.11.2 Additional RAM 21

2.11.3 Internal ROM 21

2.11.4 Memory Expansion 22

3.AVR MICROCONTROLLER

3.1 Introduction 23

3.2 Classification of AVR's 23

3.3AVR Architecture 23

3.4 Programming interfaces 24

3.4.1 ISP 24

3.4.2PDI 25

3.4.3 High voltage serial 25

3.4.4High voltage parallel 25

3.4.5 Bootloader 25

3.4.6 ROM 25

3.3.6 aWire 26

3.5 CHARACTERISTICS OF AVR 26

4.ATmega8 Microcontroller

4.1 Introduction 27

4.2 Pin Diagram 27

4.3 Pin Description 28

4.4 Internal Architecture 29

4.5 Features 30

4.6 PROGRAMMING IN ATmega8 31

4.7 Interfacing Of Data Bus With Different Units 32

5.Interfacing with ATmega8

5.1 LED 33

5.2 LCD 34

5.2.1 LCD controller 35

5.2.2 LCD Display 35

5.2.3 Configurations 37

5.3 Seven segment display 37

5.4 Relay 39

5.5 DC Motor 41

5.5.1 L293D 42

5.5.2Pin diagram 42

5.6 DTMF 43

5.6.1 HT9170 44

5.6.2 PIN diagram 45

5.6.3 Pin Description 45

5.7 ADC Interfacing 46

5.7.1 DAC 46

5.7.2 Interfacing with ATmega8 46

5.7.3 Temperature Sensor 48

5.7.4 LM35 48

5.8 Serial Communication 49

5.8.1 RS-232 49

5.8.2 I2C 49

5.8.3 SPI 49

5.8.4 DTE DCE Devices 49

5.8.5 UART 50

5.9 Interfacing of pc to microcontroller 51

5.10 Interfacing of microcontroller to PC

6 .Conclusion 52

List Of Figures

S.No Title Page. No

1. Fig:1.1 uses of embedded system 2

2. Fig:1.2 Architecture of Embedded system 7

3. Fig:1.3 Block diag of microcontroller 10

4. Fig:2.1 Block Diag of 8051 12

5. Fig 2.2 PIN diag of 8051 14

6. Fig:2.3 Crystal oscillator of 8052 15

7. Fig:2.4 Accumulator Register 17

8. Fig:2.5 B register 17

9. Fig:2.6 Program Status Word Register 18

10. Fig:2.7 Data Pointer Register 19

11. Fig:2.8 Stack Pointer Register 20

12. Fig:2.9 RAM Memory Space Allocation 21

13. Fig:3.1 AVR Architecture 22

14. Fig:4.1 Pin diag of ATmega8 27

15. Fig:4.2 Architecture of ATmega8 29

16. Fig :4.3 Registers of ATmega8 31

17. Fig:5.1 LED 33

18. Fig:5.2 Interfacing of LED 34

19. Fig: 5.3 LCD 35

20. Fig:5.4 Interfacing of LCD 36

21. Fig:5.5 Prototype of LCD 37

22. Fig:5.6 SevenSegment Display 38

23. Fig:5.7 Common anode 38

24. Fig:5.8 Common cathode 38

25. Fig:5.9 Interfacing of seven segment 39

26. Fig:5.10 Relay 40

27. Fig:5.11 Interfacing of relay 41

28. Fig:5.12 Interfacing of dc motor 41

29. Fig:5.13 Pin diagram of L293D 42

30. Fig:5.14 Dc motor with Atmega8 42

31. Fig:5.15 DTMF 43

32. Fig:5.16 Flow chart fot DTMF 44

33. Fig:5.17 Pin diagram of HT9170 45

34. Fig:5.18 Temp.Sensor with ATmega8 48

35. Fig:5.19 LM35 48

36. Fig:5.20 Serial transmission 49

37. Fig:5.21 Max 232IC 49

38. Fig:5.22 Interfacing of PC with microcontroller 51

ACKNOWLEDGEMENT

I would like to extend my heartfelt thanks and deep sense of gratitude to all those who helped me in practical

training .First and foremost, I would like to express my sincere thanks to the trainer, Mr.Rahul Agrawal

and entire staff at training centre from the core of my heart because they encouraged and persuaded me to

get a well training.

I would like to express my thanks to my guide Ms.Pushpa Gothwal for the inspiration and blessings

bestowed upon me by them.

I am indebted to all my colleagues for guiding and helping me in the preparation of the training report. The

most sincere and important acknowledgement and gratitude is to my parents, who have given their moral

boosting support and encouragement at every stage of this Endeavour.

In the end, I convey my thanks to all those who extend their cooperation directly or indirectly in completion

of the training report.

Shivangi Dwivedi

ABSTRACT

Embedded systems are increasingly becoming integral parts of almost all technology-

oriented applications. Embedded systems are the unsung heroes of much of the

technology we use today- video games, washing machines etc. The appliances using

embedded systems are pre programmed to perform a dedicated or narrow range of

functions as part of a large system, usually with minimal end user interaction and

optimum performance. Embedded systems are used in navigation tools like global

positioning systems (GPS), automated teller machines(ATM’s), networking

equipments such as Echo cancellation, facsimile etc. the coming together of embedded

systems and the internet, which made possible the networking of several embedded

systems to operate as part of a large system across networks- be it a LAN, WAN, or

the Internet. This convergence of embedded systems with the Internet is going to

transfer the way we live.

The Embedded systems are fast achieving ubiquity, blurring the lines between science

fiction and hard reality.

1

1. Embedded System

1.1 Introduction

Microcontroller are widely used in Embedded System products. An Embedded product uses

the microprocessor(or microcontroller) to do one task & one task only. A printer is an

example of Embedded system since the processor inside it perform one task only namely

getting the data and printing it. Although microcontroller are preferred choice for many

Embedded systems, There are times that a microcontroller is inadequate for the task. For this

reason in recent years many manufactures of general purpose microprocessors such as

INTEL, Motorolla, AMD & Cyrix have targeted their microprocessors for the high end of

Embedded market.One of the most critical needs of the embedded system is to decrease

power consumptions and space. This can be achieved by integrating more functions into the

CPU chips. All the embedded processors have low power consumptions in additions to some

forms of I/O,ROM all on a single chip. In higher performance Embedded system the trend is

to integrate more & more function on the CPU chip & let the designer decide which feature

he/she wants to use.

Embedded System

An Embedded System employs a combination of hardware & software to perform a specific

function. Software is used for providing features and flexibility hardware(Processors,

Memory...) is used for performance & sometimes security.An embedded system is a special

purpose system in which the computer is completely encapsulated by the device it controls.

Unlike a general purpose computer, such as a PC, an embedded system performs predefined

task’s usually with very specific tasks design engineers can optimize it reducing the size and

cost of the product. Embedded systems are often mass produced, so the cost savings may be

multiplied by millions of items.The core of any embedded system is formed by one or several

microprocessor or micro controller programmed to perform a small number of tasks. In

contrast to a general purpose computer, which can run any software application, the user

chooses, the software on an embedded system is semi-permanent, so it is often called

firmware.

1.2 Examples of Embedded System

1. Automated tiller machines (ATMS).

2

2. Integrated system in aircraft and missile.

3.Cellular telephones and telephonic switches.

4. Computer network equipment, including routers timeservers and firewalls

5. Computer printers, Copiers.

6. Disk drives (floppy disk drive and hard disk drive)

7. Engine controllers and antilock brake controllers for automobiles.

8. Home automation products like thermostat, air conditioners sprinkles and security

monitoring system.

9. House hold appliances including microwave ovens, washing machines, TV sets DVD

players/recorders.

10. Medical equipment.

11. Measurement equipment such as digital storage oscilloscopes, logic analyzers and

spectrum analyzers.

12. Multimedia appliances: internet radio receivers, TV set top boxes.

13. Small hand held computer with P1M5 and other applications.

14. Programmable logic controllers (PLC’s) for industrial automation and monitoring.

15. Stationary video game controllers.

Fig: 1.1

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1.3 Characteristics of an Embedded System : The important characteristics of an

embedded system are

Speed (bytes/sec) : Should be high speed

Power (watts) : Low power dissipation

Size and weight : As far as possible small in size and low weight

Accuracy (% error) : Must be very accurate

Adaptability : High adaptability and accessibility.

Reliability : Must be reliable over a long period of time.

So,an embedded system must perform the operations at a high speed so that it can be

readily used for real time applications and its power consumption must be very low and the

size of the system should be as for as possible small and the readings must be accurate with

minimum error.The system must be easily adaptable for different situations.

1.4 CATEGORIES OF EMBEDDED SYSTEMS : Embedded systems can be

classified into the following 4 categories based on their functional and performance

requirements.

Stand-alone embedded systems

Real-time embedded systems -- Hard real-time systems & Soft real-time system

Networked embedded systems and

Mobile Embedded systems.

Based on the performance of the Microcontroller they are also classified into (i) Small scaled

embedded system (ii) Medium scaled embedded system and (iii) Large scaled embedded

system.

Stand alone Embedded systems : A stand-alone embedded system works by itself. It is a

self-contained device which do not require any host system like a computer.. It takes either

digital or analog inputs from its input ports, calibrates, converts, and processes the data, and

outputs the resulting data to its attached output device, which either displays data, or controls

and drives the attached devices. Temperature measurement systems, Video game consoles ,

MP3 players, digital cameras, and microwave ovens are the examples for this category.

Real-time embedded systems : An embedded system which gives the required output in a

specified time or which strictly follows the time dead lines for completion of a task is known

as a Real time system. i.e a Real Time system , in addition to functional correctness, also

satisfies the time constraints .

4

There are two types of Real time systems.(i) Soft real time system and (ii) Hard real time

system.

Soft Real-Time system : A Real time system in which ,the violation of time constraints will

cause only the degraded quality, but the system can continue to operate is known as a Soft

real time system. In soft real-time systems, the design focus is to offer a guaranteed

bandwidth to each real-time task and to distribute the resources to the tasks.

Ex: A Microwave Oven , washing machine ,TV remote etc.

Hard Real-Time system : A Real time system in which ,the violation of time constraints will

cause critical failure and loss of life or property damage or catastrophe is known as a Hard

Real time system.

These systems usually interact directly with physical hardware instead of through a human

being .The hardware and software of hard real-time systems must allow a worst case

execution (WCET) analysis that guarantees the execution be completed within a strict

deadline. The chip selection and RTOS selection become important factors for hard real-time

system design.

Ex: Deadline in a missile control embedded system , Delayed alarm during a Gas leakage ,

car airbag control system , A delayed response in pacemakers ,Failure in RADAR

functioning etc.

Networked embedded systems : The networked embedded systems are related to a network

with network interfaces to access the resources. The connected network can be a Local

Area Network (LAN) or a Wide Area Network (WAN), or the Internet. The connection can

be either wired or wireless.

The networked embedded system is the fastest growing area in embedded systems

applications. The embedded web server is such a system where all embedded devices are

connected to a web server and can be accessed and controlled by any web browser.

Ex: A home security system is an example of a LAN networked embedded system where all

sensors (e.g. motion detectors, light sensors, or smoke sensors) are wired and running on the

TCP/IP protocol.

Mobile Embedded systems : The portable embedded devices like mobile and cellular phones

, digital camaras,MP3 players, PDA (Personal Digital Assistants) are the example for mobile

embedded systems. The basic limitation of these devices is the limitation of memory and

other resources.

5

Small scaled embedded system : An embedded system supported by a single 8–16 bit

Microcontroller with on-chip RAM and ROM designed to perform simple tasks is a Small

scale embedded system.

Medium scaled embedded system : An embedded system supported by 16–32 bit

Microcontroller /Microprocessor with external RAM and ROM that can perform more

complex operations is a Medium scale embedded system.

Large scaled embedded system: An embedded system supported by 32-64 bit multiple

chips which can perform distributed jobs is considered as a Large scale embedded system.

1.5 Application Areas of Embedded Systems: The embedded systems have a huge

variety of application domains which varies from very low cost to very high cost and from

daily life consumer electronics to industry automation equipments, from entertainment

devices to academic equipments, and from medical instruments to aerospace and weapon

control systems. So,the Embedded systems span all aspects of our modern life. The following

table gives the various applications of embedded systems.

S.No Embedded System Application

1 Home Appliances Dishwasher, washing machine, microwave, Top-set

box, security system , HVAC system, DVD,

answering machine, garden sprinkler systems etc..

2 Office Automation Fax, copy machine, smart phone system, modern,

scanner, printers.

3 Security Face recognition, finger recognition, eye recognition,

building security system , airport security system,

alarm system.

4 Academia Smart board, smart room, OCR, calculator, smart

cord.

5 Instrumentation Signal generator, signal processor, power

supplier,Process instrumentation,

6 Telecommunication Router, hub, cellular phone, IP phone, web camera

7 Automobile Fuel injection controller, anti-locking brake system,

air-bag system, GPS, cruise control.

8 Entertainment MP3, video game, Mind Storm, smart toy.

9 Aerospace Navigation system, automatic landing system, flight

attitude controller, space explorer, space robotics.

6

10 Industrial automation Assembly line, data collection system, monitoring

systems on pressure, voltage, current, temperature,

hazard detecting system, industrial robot.

11 Personal PDA, iPhone, palmtop, data organizer.

12 Medical CT scanner, ECG , EEG , EMG ,MRI, Glucose

monitor, blood pressure monitor, medical diagnostic

device.

13 Banking & Finance ATM, smart vendor machine, cash register ,Share

market

14 Miscellaneous: Elevators, tread mill, smart card, security door etc.

Table no. 1.1

1.6 Overview of embedded systems architecture:

Every embedded system consists of customer-built hardware components supported by a

Central Processing Unit (CPU), which is the heart of a microprocessor (µP) or

microcontroller (µC). A microcontroller is an integrated chip which comes with built-in

memory, I/O ports, timers, and other components. Most embedded systems are built on

microcontrollers, which run faster than a custom-built system with a microprocessor, because

all components are integrated within a single chip. Operating system play an important role

in most of the embedded systems. But all the embedded systems do not use the operating

system. The systems with high end applications only use operating system. To use the

operating system the embedded system should have large memory capability. So, This is not

possible in low end applications like remote systems, digital cameras,MP3 players , robo toys

etc.The architecture of an embedded system with OS can be denoted by layered structure as

shown below. The OS will provide an interface between the hardware and application

software. will run the application with out any host system.

Coming to the hardware details of the embedded system, it consists of the following

important blocks.

CPU(Central Processing Unit)

RAM and ROM

I/O Devices

Communication Interfaces

Sensors etc. (Application specific circuitary)

This hardware architecture can be shown by the following block diagram.

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Fig: 1.2

Central Processing Unit : A CPU is composed of an Arithmetic Logic Unit (ALU), a Control

Unit (CU), and many internal registers that are connected by buses. The ALU performs all

the mathematical operations (Add, Sub, Mul, Div), logical operations (AND, OR), and

shifting operations within CPU .The timing and sequencing of all CPU operations are

controlled by the CU, which is actually built of many selection circuits including latches and

decoders .The CU is responsible for directing the flow of instruction and data within the CPU

and continuously running program instructions step by step.

The CPU works in a cycle of fetching an instruction, decoding it, and executing it, known as

the fetch-decode-execute cycle. The cycle begins when an instruction is fetched from a

memory location pointed to by the PC to the IR via the data bus.

For embedded system design, many factors impact the CPU selection, e.g., the maximum size

(number of bits) in a single operand for ALU (8, 16, 32, 64 bits), and CPU clock frequency

for timing tick control, i.e. the number of ticks (clock cycles) per second in measures of MHz.

Memory : Embedded system memory can be either on-chip or off-chip. On chip memory

access is much fast than off-chip memory, but the size of on-chip memory is much smaller

than the size of off-chip memory. Usually, it takes at least two I/O ports as external address

lines plus a few control lines such as R/W and ALE control lines to enable the extended

memory. Generally the data is stored in RAM and the program is stored in ROM.

8

I/O Ports : The I/O ports are used to connect input and output devices. The common input

devices for an embedded system include keypads, switches, buttons, knobs, and all kinds of

sensors (light, temperature, pressure, etc).

The output devices include Light Emitting Diodes (LED), Liquid Crystal Displays (LCD),

printers, alarms, actuators, etc. Some devices support both input and output, such as

communication interfaces including Network Interface Cards (NIC), modems, and mobile

phones.

Communication Interfaces :To transfer the data or to interact with other devices ,the

embedded devices are provided the various communication interfaces like RS232, RS422,

RS485 ,USB, SPI(Serial Peripheral Interface ) ,SCI (Serial Communication Interface)

,Ethernet etc.

Application Specific Circuitry : The embedded system some times receives the input from a

sensor or actuator. In such situations certain signal conditioning circuitry is needed. This

hardware circuitry may contain ADC , Op-amps ,DAC etc. Such circuitry will interact with

the embedded system to give correct output.

Power supply: Most of the embedded systems now days work on battery operated supplies.

Because low power dissipation is always required. Hence the systems are designed to work

with batteries.

1.7 Specialties of an Embedded Systems : An embedded system has certain

specialties when compared to a normal computer system or a workstation or a mainframe

computer system.

(i).Embedded systems are dedicated to specific tasks, whereas PCs are generic computing

platforms.

(ii).Embedded systems are supported by a wide array of processors and processor

architectures

(iii). Embedded systems are usually cost sensitive.

(iv). Embedded systems have real-time constraints.

(v).If an embedded system use an operating system , it is most likely using a real-time

perating system (RTOS), but not Windows 9X, Windows NT, Windows 2000, Unix,

Solaris, etc.

(vi). The implications of software failure is much more severe in embedded systems than in

desktop systems.

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(vii) Embedded systems often have power constraints.

(ix). Embedded systems must be able to operate under extreme environmental conditions.

(x). Embedded systems utilizes fewer system resources than desktop systems.

(xi). Embedded systems often store all their object code in ROM.

(xii). Embedded systems require specialized tools and methods to be efficiently designed

when compared to desktop computers.

(xiii). Embedded microprocessors often have dedicated debugging circuitry.

(xiv).Embedded systems have Software Up gradation capability

(xv). Embedded systems have large User Interfaces for real time applications.

DIFFERENT TYPES OF PROCESSORS OF EMBEDDED SYSTEMS

1.Microprocessors

2.Microcontrollers

3.Digital signal processor.

1.8 Microprocessor (MPU)

A microprocessor is a general-purpose digital computer central processing unit(CPU).

Although popularly known as a ―computer on a chip‖ is in no sense a complete digital

computer. The block diagram of a microprocessor CPU is shown, which contains an

arithmetic and logical unit (ALU), a program counter (PC), a stack pointer (SP),some

working registers, a clock timing circuit, and interrupt circuits.

1.9 Microcontroller (MCU)

Figure shows the block diagram of a typical microcontroller. The design incorporates all of

the features found in micro-processor CPU: ALU, PC, SP, and registers. It also added the

other features needed to make a complete computer: ROM, RAM, parallel I/O, serial I/O,

counters, and clock circuit.

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Fig:1.3

1.10 Comparision Between Microprocessor And Microcontroller

The microprocessor must have many additional parts to be operational as a computer whereas

microcontroller requires no additional external digital parts.

1. The prime use of microprocessor is to read data, perform extensive calculations on that

data and store them in the mass storage device or display it. The prime functions of

microcontroller is to read data, perform limited calculations on it, control its environment

based on these data. Thus the microprocessor is said to be general-purpose digital computers

whereas the microcontroller are intend to be special purpose digital controller.

2. Microprocessor need many opcodes for moving data from the external memory to the

CPU, microcontroller may require just one or two, also microprocessor may have one or two

types of bit handling instructions whereas microcontrollers have many.

3. Thus microprocessor is concerned with the rapid movement of the code and data from the

external addresses to the chip, microcontroller is concerned with the rapid movement of the

bits within the chip.

4. Lastly, the microprocessor design accomplishes the goal of flexibility in the hardware

configuration by enabling large amounts of memory and I/O that could be connected to the

address and data pins on the IC package. The microcontroller design uses much more limited.

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1.11 Types of Microcontroller:

Microcontrollers are divided into categories according to their memory, architecture, bits and

instruction sets. So let’s discuss types of microcontrollers:-

Bits:

8 bits microcontroller executes logic & arithmetic operations. Examples of 8 bits micro

controller is Intel 8031/8051.

16 bits microcontroller executes with greater accuracy and performance in contrast to 8-bit.

Example of 16 bit microcontroller is Intel 8096.

32 bits microcontroller is employed mainly in automatically controlled appliances such as

office machines, implantable medical appliances, etc. It requires 32-bit instructions to carry

out any logical or arithmetic function.

Memory:

External Memory Microcontroller – When an embedded structure is built with a

microcontroller which does not comprise of all the functioning blocks existing on a chip it

is named as external memory microcontroller. For illustration- 8031 microcontroller does

not have program memory on the chip.

Embedded Memory Microcontroller – When an embedded structure is built with a

microcontroller which comprise of all the functioning blocks existing on a chip it is named

as embedded memory microcontroller. For illustration- 8051 microcontroller has all

program & data memory, counters & timers, interrupts, I/O ports and therefore its

embedded memory microcontroller.

Instruction Set:

CISC- CISC means complex instruction set computer, it allows the user to apply 1

instruction as an alternative to many simple instructions.

RISC- RISC means Reduced Instruction Set Computers. RISC reduces the operation time

by shortening the clock cycle per instruction.

Memory Architecture:

Harvard Memory Architecture Microcontroller

Princeton Memory Architecture Microcontroller

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2.8051 Microcontroller

THE 8051 ARCHITECTURE

2.1About the 8051

The Intel 8051 is an 8-bit microcontroller which means that most available operations are

limited to 8 bits. There are 3 basic "sizes" of the 8051: Short, Standard, and Extended. The

Short and Standard chips are often available in DIP (dual in-line package) form, but the

Extended 8051 models often have a different form factor, and are not "drop-in compatible".

2.2 Block Diagram

Figure 2.1:Block Diagram of 8051

All these things are called 8051 because they can all be programmed using 8051 assembly

language, and they all share certain features (although the different models all have their own

special features).Some of the features that have made the 8051 popular are:

4 KB on chip program memory.

128 bytes on chip data memory(RAM).

4 register banks.

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8-bit data bus

16-bit address bus

32 general purpose registers each of 8 bits

16 bit timers (usually 2, but may have more, or less).

3 internal and 2 external interrupts.

Bit as well as byte addressable RAM area of 16 bytes.

Four 8-bit ports, (short models have two 8-bit ports).

16-bit program counter and data pointer.

1 Microsecond instruction cycle with 12 MHz Crystal.

8051 models may also have a number of special, model-specific features, such as

UARTs, ADC, OpAmps, etc...

2.3 Typical applications

8051 chips are used in a wide variety of control systems, telecom applications, and

robotics as well as in the automotive industry. By some estimation, 8051 family chips

make up over 50% of the embedded chip market.The 8051 has been in use in a wide

number of devices, mainly because it is easy to integrate into a project or build a

device around. The following are the main areas of focus:

1.Energy Management:Efficient metering systems help in controlling energy usage in

homes and industrial applications. These metering systems are made capable by

incorporating microcontrollers.

2.Touch screens:A high number of microcontroller providers incorporate touch-

sensing capabilities in their designs. Portable electronics such as cell phones, media

players and gaming devices are examples of microcontroller-based touch screens.

3.Automobiles: The 8051 finds wide acceptance in providing automobile solutions.

They are widely used in hybrid vehicles to manage engine variants. Additionally,

functions such as cruise control and anti-brake system have been made more efficient

with the use of microcontrollers. So the microcontroller 8051 has great advantage in

the field of the automobiles.

4. Medical Devices: Portable medical devices such as blood pressure and glucose

monitors

use microcontrollers will to display data, thus providing higher reliability in providing

medical results.

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2.4 Pinout Description

Fig:2.2

Pin 1-8(Port 1): Each of these pins can be configured as an input or an output.

Pin 9(RST): A logic one on this pin disables the microcontroller and clears the contents

ofmost registers. In other words, the positive voltage on this pin resets the microcontroller.

By applying logic zero to this pin, the program starts execution from the beginning. Pin 9 is

the RESET pin. It is an input and is active high. Upon applying a high pulse to this pin the

microcontroller well reset and terminate all activities. This is often referred to as a power on

reset .Activating a power on reset will cause all values the registers to be lost. It will set

program counter to all 0s.In order for the RESET input to be effective it must have a

minimum duration of two machine cycles. In other words the high pulse must be high for a

minimum of two machine cycles before it is allowed to go low.

Pin 10-17(Port 3): Similar to port 1, each of these pins can serve as general input or output.

Besides, all of them have alternative functions:

Pin 10(RXD):Serial asynchronous communication input or Serial synchronous

communication output.

15

Pin 11(TXD):Serial asynchronous communication output or Serial synchronous

communication clock output.

Pin 12(INT0):Interrupt 0 input.

Pin 13(INT1):Interrupt 1 input.

Pin 14(T0):Counter 0 clock input.

Pin 15(T1):Counter 1 clock input.

Pin 16(WR):Write to external (additional) RAM.

Pin 17(RD):Read from external RAM.

Pin 18, 19(X2,X1):Internal oscillator input and output. The 8051 has an on chip oscillator but

requires an external clock to run it. Most often a quartz crystal oscillator is connected to

inputs XTAL1 (pin 19) and XTAL2 (pin 18). The quartz crystal oscillator connected to

XTAL1 and XTAL2 also needs two capacitors of 30 pf value. One side of each capacitor is

connected to the ground. Speed refers to the maximum oscillator frequency connected to

XTAL

Fig:2.3

Pin 20(GND):Ground.

Pin 21-28(Port 2):If there is no intention to use external memory then these port pins are

configured as general inputs/outputs. In case external memory is used, the higher address

byte, i.e. addresses A8-A15 will appear on this port. Even though memory with capacity of

64Kb is not used, which means that not all eight port bits are used for its addressing, the rest

of them are not available as inputs/outputs.

16

Pin 29(PSEN):This is an output pin. PSEN stands for ―program store enable‖. If external

ROM is used for storing program then a logic zero (0) appears on it every time the

microcontroller reads a byte from memory.

Pin 30(ALE):ALE stands for ―address latch enable. It is an output pin and is active high.

When connecting an 8031 to external memory, port 0 provides both address and data. In

other words the 8031 multiplexes address and data through port 0 to save pins. The ALE pin

is used for de-multiplexing the address and data.

Pin 31(EA):EA which stands for ―external access‖ is pin number 31 in the DIP packages. It is

an input pin and must be connected to either Vcc or GND. In other words it cannot be

unconnected. By applying logic zero to this pin, P2 and P3 are used for data and address

transmission with no regard to whether there is internal memory or not. It means that even

there is a program written to the microcontroller, it will not be executed. Instead, the program

writtento external ROM will be executed. By applying logic one to the EA pin, the

microcontroller will use both memories, first internal then external (if exists).

Pin 32-39(Port 0): Similar to P2, if external memory is not used, these pins can be used as

general inputs/outputs. Otherwise, P0 is configured as address output (A0-A7) when the ALE

pin is driven high (1) or as data output (Data Bus) when the ALE pin is driven low (0).

Pin 40(Vcc):+5V power supply.

2.5 Programming Model Of 8051

In programming model of 8051 we have different types of registers are available and these

registers are used to store temporarily data is then the information could be a byte of data to

be processed or an address pointing to the data to be fetched the majority of registers is 8051

are 8-bikt registers.

2.6 Accumulator (Register A)

Accumulator is a mathematical register where all the arithmetic and logical operations are

done is this register and after execution of instructions the outpour data is stored in the

register is bit addressable near. We can access any of the single bit of this register.A register

is a general-purpose register used for storing intermediate results obtained during operation.

Prior to executing an instruction upon any number or operand it is necessary to store it in the

accumulator first. All results obtained from arithmetical operations performed by the ALU

are stored in the accumulator. Data to be moved from one register to another must go through

17

the accumulator. In other words, the A register is the most commonly used register and it is

impossible to imagine a microcontroller without it. More than half instructions used by the

8051 microcontroller use somehow the accumulator.

Figure2.4:Accumulator Register

2.7 B Register:

B register is same as that of accumulator of. It is also an 8 bit register and every bit of this is

accessible. This is also a mathematical register B which is used mostly for multiplication and

division.

Figure2.5:B register

2.8 PSW (Program Status Word) Register

Program status word register is an 8 bit register. It is also referred to as the flag register.

Although the PSW register is 8 bits wide, only 6 bits of it are used by the 8051. The unused

bits are user-definable flags. Four of the flags are called conditional flags, meaning that they

Indicate some conditions that result after an instruction is executed. These four are CY

(carry), AC (auxiliary carry), P (parity) and OV (overflow).

CY PSW.7 Carry Flag

AC PSW.6 Auxiliary Carry Flag

F0 PSW.5 Available to the user for

General Purpose

RS1 PSW.4 Register Bank Selector Bit 1

RS0 PSW.3 Register Bank Selector

Bit 0

OV PSW.2 Overflow Flag

-- PSW.1 User Definable Bit

P PSW.0 Parity Flag.

18

Figure2.6: Program Status Word Register

PSW register is one of the most important SFRs. It contains several status bits that reflect the

current state of the CPU. Besides, this register contains Carry bit, Auxiliary Carry, two

register bank select bits, Overflow flag, parity bit and user-definable status flag.

RS1 (PSW.4) RS0 (PSW.3)

Bank 0 0 0

Bank 1 0 1

Bank 2 1 0

Bank 3 1 1

Table 2.1: PSW Bit Bank selection

P (Parity bit): If a number stored in the accumulator is even then this bit will be automatically

set (1), otherwise it will be cleared (0). It is mainly used during data transmit and receive via

serial communication.

Bit 1: This bit is intended to be used in the future versions of microcontrollers.

OV( Overflow): Occurs when the result of an arithmetical operation is larger than 255 and

cannot be stored in one register. Overflow condition causes the OV bit to be set (1).

Otherwise, it will be cleared (0).

1RS0, RS1 (Register bank select bits): These two bits are used to select one of four register

banks of RAM. By setting and clearing these bits, registers R0-R7 are stored in one of four

banks of RAM.

F0 (Flag 0): This is a general-purpose bit available for use.

AC (Auxiliary Carry Flag):This is used for BCD operations only.

19

CY (Carry Flag):This is the (ninth) auxiliary bit used for all arithmetical operations and shift

instructions.

2.9 Data Pointer Register (DPTR)

DPTR register is not a true one because it doesn't physically exist. It consists of two separate

registers: DPH (Data Pointer High) and (Data Pointer Low). For this reason it may be treated

as a 16-bit register or as two independent 8-bit registers. Their 16 bits are primarly used for

external memory addressing. Besides, the DPTR Register is usually used for storing data and

intermediate results.

Figure 2.7:Data Pointer Register

2.10 Stack Pointer (SP) Register

Figure2.8:Stack Pointer Register

A value stored in the Stack Pointer points to the first free stack address and permits stack

availability. Stack pushes increment the value in the Stack Pointer by 1. Likewise, stack pops

decrement its value by 1. Upon any reset and power-on, the value 7 is stored in the Stack

Pointer, which means that the space of RAM reserved for the stack starts at this location. If

another value is written to this register, the entire Stack is moved to the new memory

location.

20

2.11 Internal Memory

The 8051 has two types of memory and these are Program Memory and Data Memory.

Program Memory (ROM) is used to permanently save the program being executed, while

Data Memory (RAM) is used for temporarily storing data and intermediate results created

and used during the operation of the microcontroller. 128 or 256 bytes of RAM is used.

2.11.1 Internal RAM

As already mentioned, Data Memory is used for temporarily storing data and intermediate

results created and used during the operation of the microcontroller. Besides, RAM memory

built in the 8051 family includes many registers such as hardware counters and timers,

input/output ports, serial data buffers etc. The previous models had 256 RAM locations,

while for the later models this number was incremented by additional 128 registers. However,

the first 256 memory locations (addresses 0-FFh) are the heart of memory common to all the

models belonging to the 8051 family. Locations available to the user occupy memory space

with addresses 0-7Fh, i.e. first 128 registers. This part of RAM is divided in several blocks.

The first block consists of 4 banks each including 8 registers denoted by R0-R7. Prior to

accessing any of these registers, it is necessary to select the bank containing it. The next

memory block (address 20h-2Fh) is bit- addressable, which means that each bit has its own

address (0-7Fh). Since there are 16 such registers, this block contains in total of 128 bits with

separate addresses (address of bit 0 of the 20h byte is 0, while address of bit 7 of the 2Fh byte

is 7Fh). The third group of registers occupy addresses 2Fh-7Fh, i.e. 80 locations, and does not

have any special functions or features.

21

Figure2.9: RAM Memory Space Allocation

2.11.2 Additional RAM

In order to satisfy the programmers’ constant hunger for Data Memory, the manufacturers

decided to embed an additional memory block of 128 locations into the latest versions of the

8051 microcontrollers. However, it’s not as simple as it seems to be… The problem is that

electronics performing addressing has 1 byte (8 bits) on disposal and is capable of reaching

only the first 256 locations, therefore. In order to keep already existing 8-bit architecture and

compatibility with other existing models a small trick was done.What does it mean? It means

that additional memory block shares the same addresses with locations intended for the SFRs

(80h- FFh). In order to differentiate between these two physically separated memory spaces,

different ways of addressing are used. The SFRs memory locations are accessed by direct

addressing, while additional RAM memory locations are accessed by indirect addressing.

2.11.3 Internal ROM

The first models of the 8051 microcontroller family did not have internal program memory. It

was added as an external separate chip. These models are recognizable by their label

beginning with 803 (for example 8031 or 8032). All later models have a few Kbyte ROM

embedded. Even though such an amount of memory is sufficient for writing most of the

programs, there are situations when it is necessary to use additional memory as well. A

22

typical example are so called lookup tables. They are used in cases when equations

describing some processes are too complicated or when there is no time for solving them. In

such cases all necessary estimates and approximates are executed in advance and the final

results are put in the tables (similar to logarithmic tables).EA=0In this case, the

microcontroller completely ignores internal program memory and executes only the program

stored in external memory.EA=1In this case, the microcontroller executes first the program

from built-in ROM, then the program stored in external memory.In both cases, P0 and P2 are

not available for use since being used for data and address transmission. Besides, the ALE

and PSEN pins are also used.

2.11.4 Memory Expansion

In case memory (RAM or ROM) built in the microcontroller is not sufficient, it is possible to

add two external memory chips with capacity of 64Kb each. P2 and P3 I/O ports are used for

their addressing and data transmission.From the user’s point of view, everything works quite

simply when properly connected because most operations are performed by the

microcontroller itself. The 8051 microcontroller has two pins for data read RD(P3.7) and

PSEN. The first one is used for reading data from external data memory (RAM), while the

other is used for reading data from external program memory (ROM). Both pins are active

low.Even though additional memory is rarely used with the latest versions of the

microcontrollers, we will describe in short what happens when memory chips are connected

according to the previous schematic. The whole process described below is performed

automatically.Similar occurs when it is necessary to read location from external RAM.

Addressing is performed in the same way, while read and write are performed via signals

appearing on the control outputs RD (is short for read) or WR (is short for write).

23

3.AVR MICROCONTROLLER

3.1 Introduction

The AVR is a modified Harvard architecture 8-bit RISC single chip microcontroller which

was developed by Atmel in 1996. The AVR was one of the first microcontroller families to

use on-chip flash memory for program storage, as opposed to one-time programmable

ROM, EPROM, or EEPROM used by other microcontrollers at the time.

Mega AVR chips became extremely popular after they were designed into the 8-

bit Arduino platform.

The AVR is a modified Harvard architecture machine where program and data are stored in

separate physical memory systems that appear in different address spaces, but having the

ability to read data items from program memory using special instructions.

3.2 Classification of AVR's

tinyAVR — the ATtiny series

0.5–16 kB program memory

6–32-pin package

Limited peripheral set

megaAVR — the ATmega series

4–512 kB program memory

28–100-pin package

Extended instruction set (multiply instructions and instructions for handling larger

program memories)

Extensive peripheral set

XMEGA — the ATxmega series

16–384 kB program memory

44–64–100-pin package (A4, A3, A1)

Extended performance features, such as DMA, "Event System", and cryptography

support.

Extensive peripheral set with ADCs

Application-specific AVR

megaAVRs with special features not found on the other members of the AVR family,

such as LCD controller, USB controller, advanced PWM, CAN, etc.

FPSLIC (AVR with FPGA) FPGA 5K to 40K gates

SRAM for the AVR program code, unlike all other AVRs

AVR core can run at up to 50 MH

3.3 AVR ARCHITECTURE

• RISC architecture with CISC instruction set

24

• Powerful instruction set for C and Assembly

• Scalable

• Same powerful AVR core in all devices

• Single cycle execution

• One instruction per external clock

• Low power consumption

• 32 Working Registers

• All Directly connected to ALU!

• Very efficient core

• 20 MIPS @ 20MHz

• High System Level Integration

• Lowest total system cost

Fig:3.1

3.4 Programming interfaces

There are many means to load program code into an AVR chip. The methods to program

AVR chips varies from AVR family to family.

3.4.1 ISP

The in-system programming (ISP) programming method is functionally performed

through SPI, plus some twiddling of the Reset line. As long as the SPI pins of the AVR are

25

not connected to anything disruptive, the AVR chip can stay soldered on a PCB while

reprogramming. All that is needed is a 6-pin connector and programming adapter. This is the

most common way to develop with an AVR.

The Atmel AVR ISP mkII device connects to a computer's USB port and performs in-system

programming using Atmel's software.

AVRDUDE (AVR Downloader/UploaDEr) runs on Linux, FreeBSD, Windows, and Mac OS

X, and supports a variety of in-system programming hardware, including Atmel AVR ISP

mkII, Atmel JTAG ICE, older Atmel serial-port based programmers, and various third-party

and "do-it-yourself" programmers.

3.4.2 PDI

The Program and Debug Interface (PDI) is an Atmel proprietary interface for external

programming and on-chip debugging of XMEGA devices. The PDI supports high-speed

programming of all non-volatile memory (NVM) spaces; flash, EEPROM, fuses, lock-bits

and the User Signature Row. This is done by accessing the XMEGA NVM controller through

the PDI interface, and executing NVM controller commands. The PDI is a 2-pin interface

using the Reset pin for clock input (PDI_CLK) and a dedicated data pin (PDI_DATA) for

input and output.

3.4.3 High voltage serial

High-voltage serial programming (HVSP) is mostly the backup mode on smaller AVRs. An

8-pin AVR package does not leave many unique signal combinations to place the AVR into a

programming mode. A 12 volt signal, however, is something the AVR should only see during

programming and never during normal operation

3.4.4 High voltage parallel

High voltage parallel programming (HVPP) is considered the "final resort" and may be the

only way to fix AVR chips with bad fuse settings.

3.4.5Bootloader

Most AVR models can reserve a bootloader region, 256 B to 4 KB, where re-programming

code can reside. At reset, the bootloader runs first, and does some user-programmed

determination whether to re-program, or jump to the main application. The code can re-

program through any interface available, it could read an encrypted binary through an

Ethernet adapter like PXE. Atmel has application notes and code pertaining to many bus

interfaces.

3.4.6 ROM

The AT90SC series of AVRs are available with a factory mask-ROM rather than flash for

program memory.[21]

Because of the large up-front cost and minimum order quantity, a mask-

ROM is only cost-effective for high production runs.

26

3.4.7 aWire

aWire is a new one-wire debug interface available on the new UC3L AVR32 devices.

3.5 CHARACTERISTICS OF AVR

• High performance • Low power consumption • High code density • Advanced memory technology • High integration

27

4.ATmega8 Microcontroller

4.1 Introduction The ATmega8A has 3 timers, and 3 PWM channels. There are 6 10-bit ADC channels,

and a single analog comparator. The QFP and MLF packages have 2 more ADC channels,

for a total of 8. It is pin compatible with the newer, more powerful ATmega88/168/328

devices. It supersedes the ATmega8, which was retired in 2010. It has a wider supply

voltage range, and a faster clock than the ATmega8. ATmega8 microcontroller has 23 programmable input/output (I/O) pins which can be used

for interfacing with external world. It is possible to configure them as input or output by

setting a particular register value through programming. This IC comes in 3 different

packages, but we are using the popular 28-Pin PDIP

package (Atmega8-16PU). Note that Atmega8 is available in 2 versions; ATmega8 and

Atmega8L.

Atmega8L is a low frequency version which works up to 8MHz frequency.

CMOS RISC, ATmega8 AVR 8-BIT Microcontroller, In-system Programmable with Flash

code storage, re-programmable up to 1000 times. Features 32 working registers, single

clock cycle...

4.2 PIN DIAGRAM

Fig:4.1

28

4.3 PIN DESCRIPTION

VCC- Digital supply voltage.

GND -Ground.

Port B- (PB7..PB0)

XTAL1/XTAL2/TOSC1/

TOSC2

Port B -is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for

each bit). The Port B output buffers have symmetrical drive characteristics with both

high sink and source capability. As inputs, Port B pins that are externally pulled low

will source current if the pull-up resistors are activated. The Port B pins are tri-stated

when a reset condition becomes active, even if the clock is not running.

Depending on the clock selection fuse settings, PB6 can be used as input to the inverting

Oscillator amplifier and input to the internal clock operating circuit.

Depending on the clock selection fuse settings, PB7 can be used as output from the inverting

Oscillator amplifier.

If the Internal Calibrated RC Oscillator is used as chip clock source, PB7..6 is used as

TOSC2..1 input for the Asynchronous Timer/Counter2 if the AS2 bit in ASSR is set.

Port C- (PC5..PC0) Port C is an 7-bit bi-directional I/O port with internal pull-up resistors

(selected for each bit). The Port C output buffers have symmetrical drive characteristics

with both high sink and source capability. As inputs, Port C pins that are externally

pulled low will source current if the pull-up resistors are activated. The Port C pins are

tri-stated when a reset condition becomes active, even if the clock is not running.

PC6/RESET- If the RSTDISBL Fuse is programmed, PC6 is used as an I/O pin. Note

that the electrical characteristics of PC6 differ from those of the other pins of Port C.

If the RSTDISBL Fuse is unprogrammed, PC6 is used as a Reset input. A low level on this

pin for longer than the minimum pulse length will generate a Reset, even if the clock is not

running. The minimum pulse length is given in Table 15 on page 38. Shorter pulses are not

guaranteed to generate a Reset.

Port D (PD7..PD0)- Port D is an 8-bit bi-directional I/O port with internal pull-up resistors

(selected for each bit). The Port D output buffers have symmetrical drive characteristics with

both high sink and source capability. As inputs, Port D pins that are externally pulled low will

source current if the pull-up resistors are activated. The Port D pins are tri-stated when a reset

condition becomes active, even if the clock is not running.

RESET- Reset input. A low level on this pin for longer than the minimum pulse length will

generate a reset, even if the clock is not running.

AVCC -AVCC is the supply voltage pin for the A/D Converter, Port C (3..0), and ADC

(7..6). It should be externally connected to VCC, even if the ADC is not used. If the ADC is

used, it should be connected to VCC through a low-pass filter. Note that Port C (5..4) use

digital supply voltage, VCC.

AREF -AREF is the analog reference pin for the A/D Converter.

ADC7..6 -(TQFP and QFN/MLF Package Only)

In the TQFP and QFN/MLF package, ADC7..6 serve as analog inputs to the A/D converter

29

4.4 INTERNAL ARCHITECTURE

Fig:4.2

30

4.5 Features

Memory: It has 8 Kb of Flash program memory (10,000 Write/Erase cycles durability), 512

Bytes of EEPROM (100,000 Write/Erase Cycles). 1Kbyte Internal SRAM

I/O Ports: 23 I/ line can be obtained from three ports; namely Port B, Port C and Port D.

Interrupts: Two External Interrupt source, located at port D. 19 different interrupt vectors

supporting 19 events generated by internal peripherals.

Timer/Counter: Three Internal Timers are available, two 8 bit, one 16 bit, offering various

operating modes and supporting internal or external clocking.

SPI (Serial Peripheral interface): ATmega8 holds three communication devices integrated.

One of them is Serial Peripheral Interface. Four pins are assigned to Atmega8 to implement

this scheme of communication.

USART: One of the most powerful communication solutions is USART and ATmega8

supports both synchronous and asynchronous data transfer schemes. It has three pins assigned

for that. In many projects, this module is extensively used for PC-Micro controller

communication.

TWI (Two Wire Interface): Another communication device that is present in ATmega8 is

Two Wire Interface. It allows designers to set up a commutation between two devices using

just two wires along with a common ground connection, As the TWI output is made by

means of open collector outputs, thus external pull up resistors are required to make the

circuit.

Analog Comparator: A comparator module is integrated in the IC that provides comparison

facility between two voltages connected to the two inputs of the Analog comparator via

External pins attached to the micro controller.

Analog to Digital Converter: Inbuilt analog to digital converter can convert an analog input

signal into digital data of 10bit resolution. For most of the low end application, this much

resolution is enough.

Advanced RISC Architecture

- 130 Powerful Instructions - Most Single Clock Cycle Execution

- 32 x 8 General Purpose Working Registers

- Up to 6 MIPS Throughput at 16MHz

- Fully Static Operation

- On-chip 2-cycle Multiplier.

The 23 I/O ports of ATmega8 are organised into 3 groups:

Port B (PB0 to PB7)

Port C (PC0 to PC6)

Port D (PD0 to PD7)

31

All of these I/O pins have secondary functions, which are shown in parenthesis on the pinout

diagram shown here. Each of these registers are 8 bits wide, with each bit corresponding to a

single pin (an exception is bit 7 of the Port C register -PC6- most often used as the RESET

pin, not an I/O). Registers used for reading and writing to the I/O ports are described below.

Fig:4.3

4.6 PROGRAMMING IN ATmega8

Programming the ATmega8 is done by placing the part into RESET and applying serial

commands and data to the data in pin while clocking the sck pin. Data read back from the

part is clocked in on the data out pin.

There are commands to read and write program memory, EEPROM memory, and the

configuration area (fuse bytes, lock bits, signature bytes, and calibration bytes).

The programmer hardware consists of a 28 pin socket for the ATmega8 and a 14 pin header

for connecting to the SBC2's onboard 65C22.

The Atmega8 requires a valid clock input during programming. If the fuses are set to use an

external clock source, then one will need to be provided. I chose to use the 65C22 Timer 1

output through PB7 to supply the clock. This ensures a valid clock is always present.

Therefore, we will use Port B of the 65C22 to access the Programmer.

This simple AVR Programmer will allow you to painlessly transfer hex programs to most

ATMEL AVR microcontrollers without sacrificing your budget and time. It is more reliable

than most other simple AVR programmers available out there and can be built in very short

amount of time.

AVR programmer consists of in-circuit serial programmer (dongle) and small pcb with a DIP

socket where you can fit your microcontroller and have it quickly programmed.

You may also use this programmer as a stand alone in-circuit serial programmer that can be

used to conveniently program AVR microcontrollers without removing them from the target

circuit.

32

Entire AVR programmer has been build with using common parts and fits in the case of the

serial connector. The socket pcb has been created to fit a 28-DIP AVR ATmega8

microcontroller, but you can build a socket pcb for any other AVR microcontroller out there.

This AVR programmer is compatible with a popular PonyProg software that shows you a

status bar of the programming progress.

4.7 Interfacing Of Data Bus With Different Units

In order to maximize performance and parallelism, the AVR uses a Harvard architecture with

separate memories and buses for program and data.

Instructions in the Program memory are executed with a single level pipelining. While one

instruction is being executed, the next instruction is pre-fetched from the Program memory.

This concept enables instructions to be executed in every clock cycle.

The Program memory is In-System Reprogrammable Flash memory.The fast-access Register

File contains 32 x 8-bit general purpose working registers with a single clock cycle access

time. This allows single-cycle Arithmetic Logic Unit (ALU) operation. In a typical ALU

operation, two operands are output from the Register File, the operation is executed, and the

result is stored back in the Register File in one clock cycle.

Six of the 32 registers can be used as three 16-bit indirect address register pointers for Data

Space addressing enabling efficient address calculations. One of the these address pointers

can also be used as an address pointer for look up tables in Flash Program memory. These

added function registers are the 16-bit X, Y and Z-register.The ALU supports arithmetic and

logic operations between registers or between a constant and a register. Single register

operations can also be executed in the ALU.After an arithmetic operation, the Status Register

is updated to reflect information about the result of the operation.The Program flow is

provided by conditional and unconditional jump and call instructions, able to directly address

the whole address space. Most AVR instructions have a single 16-bit word format. Every

Program memory address contains a 16- or 32-bit instruction.

Program Flash memory space is divided in two sections, the Boot program section and the

Application program section. Both sections have dedicated Lock Bits for write and read/write

protection. The SPM instruction that writes into the Application Flash memory section must

reside in the Boot program section.During interrupts and subroutine calls, the return address

Program Counter (PC) is stored on the Stack. The Stack is effectively allocated in the general

data SRAM, and consequently the Stack size is only limited by the total SRAM size and the

usage of the SRAM. All user programs must initialize the SP in the reset routine (before

subroutines or interrupts are executed).

33

5.Interfacing with ATmega8

5.1 LED- Like a normal diode, an LED consists of a chip of semiconducting material

impregnated, or doped, with impurities to create a p-n junction. As in other diodes, current

flows easily from the p-side, or anode, to the n-side, or cathode, but not in the reverse

direction. Charge-carriers—electrons and holes—flow into the junction from electrodes with

different voltages. When an electron meets a hole, it falls into a lower energy level, and

releases energy in the form of a photon. The wavelength of the light emitted, and therefore its

color, depends on the band gap energy of the materials forming the p-n junction. In silicon or

germanium diodes, the electrons and holes recombine by a non-radiativetransition which

produces no optical emission, because these are indirect band gap materials. The materials

used for an LED have a direct band gap with energies corresponding to near-infrared, visible

or near-ultraviolet light. LED development began with infrared and red devices made with

gallium arsenide. Advances in materials science have made possible the production of devices

with ever-shorter wavelengths, producing light in a variety ofcolors.Conventional LEDs are

made from a variety of inorganic semiconductor materials, producing the following colors:

Aluminium gallium arsenide (AlGaAs) — red and infrared

Aluminium gallium phosphide (AlGaP) — green

Aluminium gallium indium phosphide (AlGaInP) — high-brightness

orange-red, orange, yellow, and green

Gallium arsenide phosphide (GaAsP) — red, orange-red, orange, and yellow

Gallium phosphide (GaP) — red, yellow and green

Gallium nitride (GaN) — green, pure green (or emerald green), and blue

also white (if it has an AlGaN Quantum Barrier)

34

Fig : 5.1

Fig :5.2

5.2 LCD

A liquid crystal display (LCD) is a thin, flat electronic visual display that uses the light

modulating properties of liquid crystals(LCs). LCs do not emit light directly.it is

an electronically-modulated optical device made up of any number of pixels filled with liquid

crystals and arrayed in front of alight source (backlight) or reflector to produce images in

colour or monochrome.

Each pixel of an LCD typically consists of a layer of molecules aligned between

two transparent electrodes, and two polarizing filters, the axes of transmission of which are

(in most of the cases) perpendicular to each other. With no actual liquid crystal between the

35

polarizing filters, light passing through the first filter would be blocked by the second

(crossed) polarizer. In most of the cases the liquid crystal has double refraction.

Before applying an electric field, the orientation of the liquid crystal molecules is determined

by the alignment at the surfaces of electrodes.

The main objective of serialLCD is to control any kind of alphanumeric LCD display using

a single signal line which communicates with LCD controller using serial communication

technique. My serialLCD prototype consist of 2 major blocks:

5.2.1 LCD controller:

It is ATmega8 microcontroller @ 8MHz internal osc. Programmed in Arduino IDE. It uses

no-xtal bootloader which provide arduino compatibility without 16Mhz external crystal &

also it is open-source. Using 8Mhz internal osc. Reduces hardware & improves power

efficiency. ATmega8 uses its native serial port (USART) to communicate with master

microcontroller. It acts as bridge between master controller & LCD. ATmega8 can be

replaced by mega168/328 without changing code. (You must change bootloader.). The

source file is provided as Firmware file in attachments.

5.2.2 LCD display:

It’s a regular 16x2 alphanumeric display. There are no more customizations in LCD.

Fig:5.3

36

Table of Pin Description of LCD :

Table:5.1

Schematic:

Fig:5.4

37

PROTOTYPE

Fig 5.5

5.2.3 Configurations

Here,PORTB(PB0-PB7) set as data port in 8 bit mode LCD display.Connect D0-D7 with the

PORTB. Ground the first lead of the lcd(vss) display.

Connect vcc to a 5v power supply.

Conncet VEE with a pot.It's used to adjust the contrast of the LCD display

15th and 16th leads are used to power the back light of the LCD.Connect 15th with 5v and

ground 16th lead.

5.3 Seven segment display interfacing

The seven-segment LED display has four individual digits, each with a decimal point. Each

of the seven segments (and the decimal point) in a given digit contains an individual LED.

When a suitable voltage is applied to a given segment LED, current flows through and

illuminates that segment LED. By choosing which segments to illuminate, any of the nine

digits can be shown. For example, as shown in the figure below, a 2 can be displayed by

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illuminating segments a, b, d, e, and g.seven segment

displays come in two varieties - common anode (CA) and

common cathode (CC). In a CA display, the anodes for the

seven segments and the decimal point are joined into a single

circuit node. To illuminate a segment in a CA display, the

voltage on a cathode must be at a suitably lower voltage

(about .7V) than the anode. In a CC display, the cathodes are

Fig:5.6 joined together, and the segments are illuminated by bringing the anode voltage

higher than the cathode node (again, by about .7V). The seven LEDs in each digit are labeled

a-g. Since the Digilab board usesCA displays, the anodes for each of the four digits are

connected in a common node, so that four separate anode circuit nodes exist (one per

digit).Similar cathode leads from each digit have also been tied together to form seven

common circuit nodes, so that one node exists for each segment type. These four anode and

seven cathode circuit nodes are available at the J2connector pins labeled A1-A4 and CA-CG.

With this scheme, any segment of any digit can be driven individually. For example, to

illuminate segments and c in the second digit, the b and c cathode nodes would be brought to

a suitable low voltage (by connecting the corresponding circuit node available at the J2

connector to ground), and anode 2 would be brought to a suitablehigh voltage (by connecting

the corresponding circuit node available at theJ2 connector to Vdd).

This will be of 2 types :

1.Common Anode

2.Common Cathode

Fig :5.7 Common anode Fig:5.8 common cathode

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Fig:5.9

5.4 Relay interfacing

The electromagnetic relay consists of a multi-turn coil, wound on an iron core, to form an

electromagnet. When the coil is energized, by passing current through it, the core becomes

temporarilymagnetized. The magnetized core attracts the iron armature. The armature is

pivoted which causes it to operate one or more sets of contacts. When the coil is de-energized

the armature and contacts are released. The coil can reenergized from a low power source

such as a transistor while the contacts can switch high powers such as the mains supply. The

relay can also be situated remotely from the control source. Relays can generate a very high

voltage across the coil when switched off.This can damage other components in the circuit.

To prevent this a diode is connected across the coil.As there are always some chances of high

voltage spikes back from the switching circuit i.e. heater so an opt coupler/isolator MCT2e is

used. It provides and electrical isolation between the microcontroller and the heater. MCT2e

is a 6-pin IC with a combination of optical transmitter LED and an optical receiver as

phototransistor. Microcontroller is connected to pin no 2 ofMCT2e through a 470-ohm

resistor. Pin no.1 is given +5V supply and pin no.4 is grounded. To handle the current drawn

by the heater a power transistor BC-369 is used as a current driver. Pin no.5 of opt coupler is

connected to the base of transistor. It takes all its output to Vandactivates the heater through

relay circuit. The electromagnetic relay consists of a multi-turn coil, wound on an iron core,

to form an electromagnet. When the coil is energized, by passing current through it, the core

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becomes temporarily magnetized. The magnetized core attracts the iron armature. The

armature is pivoted which causes it to operate one or more sets of contacts. When the coil is

de-energized the armature and contacts are released. Relays can generate a very high voltage

across the coil when switched off. This can damage other components in the circuit. To

preventthis diode is connected across the coil. Relay has five points. Out of the 2 operating

points one is permanently connected to the ground and the other point is connected to

thecollector side of the power transistor. When Vreaches the collector side i.e. signal is given

to the operating points the coil gets magnetized and attracts the iron armature. The iron plate

moves from normally connected (NC) position to normally open (NO) position. Thus the

heater gets the phase signal and is ON. To remove the base leakage voltage when no signal is

present a 470-ohmresistance is used.

Fig:5.10

The output port pins of microcontrollers can can only source few Milli amperes of current, so

they cannot be directly used to energize relays. To solve this and interface a relay with any

microcontroller or other logic chips we need a transistor.

Here you can see that output from microcontroller enter transistor via resistor R1 (4K7). This

resistor limit the current and only very small current flows from the base to the emitter. When

microcontrollers output port is in low state (0) no current flows to the base and the transistor

is in off state. When microcontroller makes the output line high (binary 1), the transistor is

switched on. Current flows from the 12v input to the relay and then to the ground via the

transistors collector pin. This current switches on the relay which in turn switches on the AC

load (the bulb)

The diode D1 (1N4007) is used as a Flyback diode. Whenever an inductive load (the the coils

of relay) is switched off, a large voltage is generated across its terminal. This voltage can

damage the transistor. To protect the transistor we put a diode in such a way that it short

circuits this voltage.

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Fig:5.11

5.5 INTERFACING OF DC MOTOR

It simply has two terminals and by reverting voltage at these terminals we can change the

direction of rotation of motor. But to run it from atmega16 microcontroller we should need to

attach a driver ic because atmega16 gives 20 mA current in output which is not sufficient to

drive a simple 12v of 1 A current rating motor. Basically L293D IC is used to drive the

motor.

Fig:5.12

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5.5.1 L293D

L293D is a typical motor driver or Motor circuit IC which allows DC motor to drive on either

directio. L293D is a 16-pin IC which can control a set of two DC motors simultaneously in

any direction.It means we can control two DC motors with a single L293D.

5.5.2 PIN DIAGRAM OF L293D.

Fig:5.13

Left input pins will regulate the rotation of motor connected across left side and right input

for motor on the right side.The motors are rotated on the basis of the inputs provided across

the inputs pins as LOGIC 0 or LOGIC 1.

Fig:5.14

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There are 4 inputs in L293D motor driver IN1,IN2 ,IN3,IN4.

These are connected to any port of the microcontroller

one motor is attatched to OUT1,OUT2

pin no.4,5,13&12 are connected to the ground.

EN1,EN2,Vss are connected to +5V supply.

5.6 DTMF INTERFACING

DTMF is a signalling system for identifying the keys or the number dialed on

a pushbutton or DTMF keypad. The early telephone systems used pulse dialling or

loop disconnect signalling. This was replaced by multi frequency (MF) dialling.

DTMF is a multi frequency tone dialling system used by the push button keypads in

telephone and mobile sets to convey the number or key dialled by the caller. DTMF

has enabled the long distance signalling of dialled numbers in voice frequency range

over telephone lines. This has eliminated the need of telecom operator between the

caller and the callee and evolved automated dialling in the telephone switching

centres.

DTMF (Dual tone multi frequency) as the name suggests uses a combination of two

sine wave tones to represent a key. These tones are called row and column

frequencies as they correspond to the layout of a telephone keypad.

Fig: 5.15

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A DTMF keypad (generator or encoder) generates a sinusoidal tone which is mixture of the

row and column frequencies. The row frequencies are low group frequencies. The column

frequencies belong to high group frequencies. This prevents misinterpretation of the

harmonics. Also the frequencies forDTMF are so chosen that none have a harmonic

relationship with the others and that mixing the frequencies would not produce sum or

product frequencies that could mimic another valid tone. The high-group frequencies (the

column tones) are slightly louder than the low-group to compensate for the high-frequency

roll off of voice audio systems.

The row and column frequencies corresponding to a DTMF keypad have been indicated in

the above figure.

DTMF tones are able to represent one of the 16 different states or symbols on the keypad.

This is equivalent to 4 bits of data, also known as nibble.

Fig:5.16

Now received tone tone is produced by ardino with the help of DTMF Decoder.

Here we used HT9170 & decodes the DTMF tone into its equivalent binary digit & this

binary number is send to the ardino ,the ardino is preprogrammed to take decisions for any

given input & outputs its decision to motor drivers in order to drive the motors in either

forward and backward directions.

5.6.1 HT9170 HT9170 is the series of Dual Tone Multi Frequency (DTMF) receivers. They employ digital

counting techniques to detect and decode the 16 DTMF tones into 4 bit output code.

HT9170 series receivers do not require any external filters as they use highly accurate

switched capacitor filters for filtering low and high frequency signals from the DTMF tones.

They also support power down (PWDN) and inhibit (INH) modes. PWDN mode is used to

power off the crystal, while INH mode to inhibit the A, B, C & D DTMF tones. The clock is

provided by a 3.58 MHz crystal.

In simple terms, HT9170 IC detects and decodes the 16 DTMF tones into 4 bit output. In case

the tones are not detected, the four output bits remain low. The DV pin goes high on

detection of a valid tone.

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5.6.2 PIN DIAGRAM OF HT9170

Fig :5.17

5.6.3Pin Description:Table 5.

Pin No Function Name

1 Operational amplifier non-inverting input VP

2 Operational amplifier inverting input VN

3 Operational amplifier output terminal GS

4 Reference voltage output terminal VREF

5 Active high. It inhibits the detection of tones corresponding

to A, B, C and D. It is internally pulled down. INH

6 Active high. It leads the chip to power down mode and

inhibits the oscillator. It is internally pulled down PWDN

7 Connection for standard 3.579545 MHz crystal

X1

8 X2

9 Ground (0V) VSS

10 Active high; Enables output D0-D3 OE

11

Output terminals

D0

12 D1

13 D2

14 D3

15 Data valid. It goes high on reception of valid DTMF signal;

otherwise remains low DV

16 Early steering output EST

17 Tone acquisition time and release time can be set by using

external resistor and capacitor RT/GT

18 Supply voltage; 5V (2.5V-5.5V) VDD

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5.7 ADC

An Analog-Digital Converter (ADC) is a widely used electronic component that converts an

analog electric signal (usually a voltage) into a digital representation. The ADCs are at the

front-end of any digital circuit that needs to process signals coming from the exterior world.

The output of a microphone, the voltage at a photodiode or the signal of an accelerometer are

examples of analog values that need to be converted so that a microprocessor can work with

them.

5.7.1 Digital to Analog Converter

In modern life, electronic equipment is frequently used in different fields such as

communication, transportation, entertainment, etc. Analog to Digital Converter (ADC) and

Digital to Analog Converter (DAC) are very important components in electronic equipment.

Since most real world signals are analog, these two converting interfaces are necessary to

allow digital electronic equipments to process the analog signals. Take the audio signal

processing in Figure 1 as an example, ADC converts the analog signal collected by audio

input equipment, such as a microphone, into a digital signal that can be processed by

computer. The computer may add sound effect such as echo and adjust the tempo and pitch of

the music. DAC converts the processed digital signal back into the analog signal that is used

by audio output equipment such as a speaker.

5.7.2 Interfacing with ATmega8

ADC means Analog to Digital converter. ADC is a inbuilt peripheral available in almost every AVR

Microcontrollers. ADC feature of Atmega8 enables us to communicate with real-world data such

as temperature, weight, pressure, voltage, resistance etc easily. Atmega8 has a ADC with

1. 6 channel (PC0 to PC5) and

2. 10 bit Resolution.

3. Here channel means the available pins (connections) in a chip that can convert analog

data into digital value separately. At the above i wrote that Atmega8 has six channels

means you can get 6 digital values of 6 analog signals separately at the same time.

4.

5. Now 10 bits resolution means 2 to the power 10 equals to 1024 division

of reference volt. means suppose we want to measure a analog voltage which is being

varied from 0 to +5 volt and reference voltage is given +5 volt then ADC circuit built

in a atmega will divide the reference volt (+5) by 1024, (5/1024=0.0048828125 volt)

and now adc value which is simply a number will be incremented by 1 on each

0.0048828125 volt, for example we give 2.5 volt to a adc channel then the digital

value will be 2.5/0.0048828125 = 512 (converted digital value of that analog volt). So

a reference voltage is a voltage (to AREF pin) to compare that analog data being

varied from 0 to reference voltage.

For connection with ATmega8

PIN 20 (AVCC) and 22 (GND) are power supply to ADC

PIN 21 (AREF) is supply pin to the reference volt of ADC.

PIN 23 to 28 are six ADC channel

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PIN 7 and 8 are power supply to main chip.

For interfacing we need 3 more registers:

1. ADCSRA (ADC Control and Status Register A)

2. ADMUX (ADC multiplexer)

3. ADC data register, ADCH and ADCL (ADC data High and Low)

ADCSRA Register

The main use of this Register is to enable the ADC features in AVR's I/O Port, Starting the

conversion of analog, Enabling Interrupt, Setting a flag bit after conversion, Declaring mode

either it will be free running or Single Conversion mode, and defining the Prescaler .

ADMUX Register This Register is used to select :

1. Reference voltage source to ADC (AREF)

2. Analog port channel to used for conversion (PC0.....PC5)

3. How the result will be stored in Data Register either Left justified or Right

justified. Since the Digital value of corresponding Analog vary from 0 to 1024, value

can't be stored in a single register that's why two registers (ADCH & ADCL) are used

to store that digital value.

ADC DATA Registers ADCH and ADCL ADCH and ADCL are Data registers used to store the Digital result, converted from Analog.

Since Atmega8 has 10 bits resolution, result may vary from 0 to 1023 (1024 in count) so that

it can not be stored in a single 8 bit register, two registers are used ADCH & ADCL (ADC

register High and Low) because Atmega8 have 8 bit architecture. By default, the result is

presented right adjusted, but can optionally be presented left adjusted by setting the ADLAR

bit in ADMU If the result is left adjusted and no more than 8-bit precision is required, it is

sufficient to read AD CH. Otherwise, ADCL must be read first, then ADCH. The ADC has

its own interrupt which can be triggered when a conversion completes. When ADC access to

the Data Registers is prohibited between reading of ADCH and ADCL, the interrupt will

trigger even if the result is lost.

5.7.3 Temperature sensor

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Fig :5.18

5.7.4 What is LM35

The LM35 is an integrated circuit sensor that can be used to measure temperature

with anelectrical output proportional to the temperature .

Fig :5.19

5.8 SERIAL COMMUNICATION

Serial communication is the process of sending data one bit at a time, sequentially, over

a communication channel or computer bus.

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Fig: 5.20

There are several popular types of serial communications. Here are a few worth noting:

RS232. Peer-to-peer (i.e. communications between two devices)

USB (Universal Serial Bus). Replaced RS232 on desktop computers.

CAN (Controller Area Network). Multi-point. Popular in the automotive industry.

SPI (Serial Peripheral Interface). Developed by Motorola. Synchronous master/slave

communications.

I2C (Inter-Integrated Circuit).Developed by Philips. Multi-master communications.

5.8.1 RS-232

RS-232 stands for Recommend Standard number 232 and C is the latest revision of the

standard. The serial ports on most computers use a subset of the RS-232C standard. The full

RS-232C standard specifies a 25-pin "D" connector of which 22 pins are used. Most of these

pins are not needed for normal PC communications, and indeed, most new PCs are equipped

with male D type connectors having only 9 pins.

• Offers a immediate link between microcontroller

to pc

.

Fig:5.21

5.8.2 I2C

I²C (Inter-Integrated Circuit), pronounced I-squared-C, is a multi-master, multi-slave, single-

ended, serial computer bus invented by Philips Semiconductor, known today as NXP

Semiconductors, used for attaching low-speed peripherals to

50

computer motherboards and embedded systems. Alternatively I²C is

spelled I2C (pronounced I-two-C) or IIC (pronounced I-I-C).

5.8.3 SPI

Serial Peripheral Interface (SPI) is a synchronous serial data protocol used by

microcontrollers for communicating with one or more peripheral devices quickly over short

distances. It can also be used for communication between two microcontrollers.

5.8.4 DCE and DTE Devices

Two terms you should be familiar with are DTE and DCE. DTE stands for Data Terminal

Equipment, and DCE stands for Data Communications Equipment. These terms are used to

indicate the pin-out for the connectors on a device and the direction of the signals on the pins.

Your computer is a DTE device, while most other devices are usually DCE devices.

If you have trouble keeping the two straight then replace the term "DTE device" with "your

PC" and the term "DCE device" with "remote device" in the following discussion.

The RS-232 standard states that DTE devices use a 25-pin male connector, and DCE devices

use a 25-pin female connector. You can therefore connect a DTE device to a DCE using a

straight pin-for-pin connection. However, to connect two like devices, you must instead use a

null modem cable.

5.8.5 UART Communication

UART is a type of asynchronous receiver/transmitter and is an integrated circuit used for

serial communications over a computer or peripheral devices serial port. It is usually used to

connect to an RS232 interface for modems, printers and similar peripherals. The UART has a

feature that, handshake lines for control of an external modem, which is controlled by

software. Most of the microcontrollers are included with the UART. For the better

coordination of data stream between computer and serial devices, buffering of data are

provided by the UARTs. Each UART contains a shift register which performs the conversion

of serial and parallel forms. The modem’s maximum transmission rate is easily handled by

the computer’s UART.

UART converts parallel data into serial data.

Baud rate=1200 Fcpu=12MHz(Tx) & 8MHz(Rx)

UBRR=(Fcpu/16baud)-1

5.9 INTERFACING OF PC AND ATmega8 (using UART)

USART means Universal Synchronous Asynchronous Transmitter and Receiver. USART

communication has provisions for full duplex communication, i.e. simultaneous transmission

and reception. Synchronous means that a single clock source would be shared by end devices

to facilitate communication. Asynchronous means, there would be no synchronized clock

source b/w the end devices. But to receive a serial incoming data there is always a need for

sampling. In addition to that, the symbol rate (i.e. the baud rate) should be known. That’s

why each USART or UART module has an internal baud rate generator module. In earlier

micro controllers, no separate baud rate generation unit was there. They used one of the

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internal timer counter for baud rate generation.

The frame (i.e. number of bits in each transmission) can consist of 5,6,7,8 or 9 data bits. Start

bit starts the data transmission. There is one/two stop bit also included. There may be an

even/odd parity bit included or there may not be any parity bits. The USART data register

(Known as UDR for AVR micro controllers) is a double buffer register. It consists of

transmitter buffer and receiver buffer. Both of them share the same I/O address. But when

Data written to UDR, the data is saved to the transmitter buffer and serially shifted out from

the TXD pin. And when UDR is read, the content in the receiver buffer is read which stores

the serial incoming bits from the RXD pins.

USART module in ATmega8 have got 5 registers (4 8-bit, 1-16bit) associated with it. They

are

1. UCSRA : USART Control and Status Register A. In this Register, three Bits indicates

the status of transmission and reception. Only two bits are enough for basic programming.

These are:

aTXC-TransmissionComplete

b) RXC-ReceptionComplete

These bits are checked before reading or writing data to UDR (USART Data Register)

2. UCSRB : Control and Status Register B. This register is very important to enable the

USART Transmitter and Receiver. The bits associated are

a) TXEN: Transmitter Enable Bit. This enables the USART transmitter.

b) RXEN: Receiver Enable Bit. This enables the USART receiver.

Fig: 5.22

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6. CONCLUSIONS:

Many embedded systems have requirements that differ significantly both in details and in

scope from desktop computers. In particular, the demands of the specific application and the

interface with external equipment may dominate the system design. Also, long life-cycles and

in some cases extreme cost sensitivity require more attention to optimization based on these

goals rather than maximizing the computational throughput.

Recent interest in hardware/software codesign is a step in the right direction, as it permits

tradeoffs between hardware and software that are critical for more cost-effective embedded

systems. However, to be successful future tools may well need to increase scope even further

to include life cycle issues and business issues.

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