EMBEDDED SYSTEM

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A

PROJECT REPORT

On

EMBEDDED SYSTEM

Submitted by

SUYASH TYAGI

In partial fulfilment for the award of the degree

Of

B.TECH

In

ELECTRONICS AND COMMUNICATION ENGINEERING

Under the Guidance

of

MR. SUMIT SINGH DHANDA

AMITY SCHOOL OF ENGINEERING TECHNOLOGY

AMITY UNVERSITY RAJASTHAN

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PREFACE

There are certain phases of professional development that cannot be

effectively taught in the academic environment. These facets can only be

learned through ground work with the industry.

The internship program can best be described as an attempt to institutionalize

efforts to bridge the gap between the professional world and the academic

institutions. Hence entire effort in internship is in terms of extending the

program of education and evaluation beyond the classroom.

Excellence is an attitude that the whole of the human race is born with. It is

the environment that makes sure that makes sure whether the results of this

attitude are visible or otherwise. A well planned, properly executed &

evaluated industrial helps a lot in inculcating a professional attitude. It

provides a linkage between the student & the industry to develop an awareness

of industrial approach to problem solving, based on a broad understanding of

process & mode of operation of organization.

The internship training helped us to gain direct, on-the-job experience,

working with successful professionals and experts in the field. Internship with

the industry also provided hands on practical experience to us on the work

culture, work ethics and work practices in the industry.

I had the opportunity to have a real experience on many ventures, which

increased my sphere of knowledge to a great extent.

SUYASH TYAGI

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ACKNOWLEDGEMENT

I have taken efforts in this project. However, it would not have been

possible without the kind support and help of many individuals and

organizations. I would like to extend my sincere thanks to all of them.

I am highly indebted to my guide MR. SUMIT SINGH DHANDA for

his guidance and constant supervision as well as for providing necessary

information regarding the project & also for his support in completing

the project.

I would like to express my gratitude towards my parents and my

program coordinator Mr. Sanyog Rawat for their kind co-operation and

encouragement which help me in completion of this project.

My thanks and appreciations also go to my colleague in developing the

project and people who have willingly helped me out with their abilities.

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Central Electronics Limited (CEL)

CEL is a Public Sector Enterprise under the Department of Scientific and Industrial

Research (DSIR), Ministry of Science & Technology, Government of India. It was

established in 1974 with an objective to commercially exploit the indigenous

technologies developed by National Laboratories and R&D Institutions in the

country. CEL is one of the rare companies, which utilized the homegrown

technologies during all these years of its existence.

CEL is pioneer in the country in the field of Solar Photovoltaic (SPV) and it has

developed state-of-the-art technology with its own R&D efforts.

CEL, pioneer in the field of Railways Safety & Signaling, has been identified as a

major indigenous agency for design and development of modern electronic Signaling

and Safety equipment by Indian Railways. The equipment manufactured in CEL

finds extreme usage in Railways in the form of Axle Counter, Axle Counter Block

System and Train Approach Warning Devices for more than 25 years.

CEL has developed a number of critical components for strategic applications and is

supplying these items to Defense.

In recognition of all these efforts, CEL has been awarded a number of times with

prestigious awards including “National Award for R&D by DSIR”.

Divisions of CEL:

The Operations of the company are divided into three Business Groups:

1. Solar Photovoltaic Group (SPV): CEL, backed by an integrated production

facility, has opened up new horizons in the field of Solar Photovoltaic. It fulfills

the various demands from rural & urban areas, thus, harnessing the solar energy.

The products of this division are Solar Cells, Modules and systems, which serve

the industrial needs of Railway Signaling, Microwave Repeaters, Defense

equipments, Obstruction warning lights at airports, etc. and rural needs such as

pumping systems for irrigation, street lighting systems, solar lanterns and rural

telecommunications.

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2. Electronic Systems Group (ESG): The Company is a pioneer in manufacturing

of Railway Signaling and Safety Equipments. It manufactures Axle Counters,

Railway Level Crossing Warning System, and solid State Interlocking System for

Railways. The other products of this division include Electronic Switching System,

Cathodic Protection System for underground pipelines and VSAT.

3. Components Group: A large range of products is manufactured here using state-

of-art technologies to meet the requirements of communications, defense,

consumer and industrial sectors.

It is divided into three sub departments. Their products and applications are as

follows:

(a) Professional Ferrites:

This department manufactures different types of ferrite cores for high frequency

applications. The different types of cores manufactured are Pot cores, E, U, I, RM,

torroids etc. These are called professional because they require highly sophisticated

techniques for their manufacture and give a superior performance. The various

applications of ferrite cores include TV sets, Communication equipments, computers,

electronic ballasts, switch mode power supplies (SMPS) and Microwave equipments.

(b) Electronic Ceramics:

This department manufactures piezo-electric transducer elements, high temperature

crucibles, high speed bearings and other alumina products. These products are used

in Defense ammunitions, Ultrasonic cleaners, Buzzers, Sonar, Gas Lighters,

Automobiles, etc.

(c) Microwave Electronics: This department manufactures microwave

components such as Phase Shifters used in Radars, Direction Finding Systems,

Frequency Correlators, Antennas, etc.

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(d) Products of CEL:

The organization manufactures different products that can be classified according to

the divisions of CEL as follows:

(i) Solar Photovoltaic Group :

Solar Cells/Modules

Solar Lantern

Street Light System

Home Light System

Water Pumping System

(ii) Electronic Systems Group :

Single / Multiple Entry / Exit Axle counters

Universal Axle counters

Block proving system

Railway Level Crossing Warning system

Solid State Interlocking System for Railways

Cathodic Protection system

Very Small Aperture Terminal (VSAT)

Electronic Switching Equipments

(iii) Components Group :

Different types of ferrite cores like Pot, RM, E, U, I, etc

Piezoelectric transducer elements

Special Bearings used in Heavy Water Plants

Microwave Ferrite Phase shifters

Direction Finding Systems

Frequency / Phase Correlator

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Index

Chapter 1 Introduction to Embedded System ……………………..1

1.1 Embedded System…………………………………………..1

1.2 Characteristics………………………………………………1

1.3 What is a controller…………………………………………2

1.4 A little history of Microcontroller…………………………..3

1.5 User interface and peripherals………………………………4

1.6 Architecture of Microcontroller……………………………..5

Cha pte r 2 Mic ro controller 8 0 51……………………………...6

2.1 pin Diagram And Pin Function……………………………..6

Chapter 3 LED Interfacing ………………………………………...13

3.1 About LED………………………………………………….13

3.2 Bi-colour LEDs……………………………………………..14

3.3 LED interfacing…………………………………………….16

Chapter 4 7- segment Display Interfacing …………………………19

4.1 7-segment Display ………………………………………….19

4.2 7-segment LEDs…………………………………………….19

4.3 7-segment LCDs…………………………………………….20

4.4 7-segment Display Interfacing……………………………...21

Chapter 5 LCD interfacing………………………………………….28

5.1 About LCD…………………………………………………28

5.2 About the Modules………………………………………….29

5.3 Power Supplies and Backlights……………………………..31

5.4 Reading and Writing………………………………………..33

5.5 LCD Interfacing …………………………………………...34

Reference………………………………………………………………36

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Chapter 1

Introduction to Embedded System

1.1 Embedded System

An embedded system is a computer system designed to do one or a few dedicated

and/or specific functions often with real-time computing constraints. It is embedded

as part of a complete device often including hardware and mechanical parts. By

contrast, a general-purpose computer, such as a personal computer (PC), is designed

to be flexible and to meet a wide range of end-user needs. Embedded systems control

many devices in common use today.

Physically, embedded systems range from portable devices such as digital watches

and MP3 players, to large stationary installations like traffic lights, factory

controllers, or the systems controlling nuclear power plants. Complexity varies from

low, with a single microcontroller chip, to very high with multiple units, peripherals

and networks mounted inside a large chassis or enclosure.

1.2 Characteristics

1. Embedded systems are designed to do some specific task, rather than be a general-

purpose computer for multiple tasks. Some also have real-time performance

constraints that must be met, for reasons such as safety and usability; others may

have low or no performance requirements, allowing the system hardware to be

simplified to reduce costs.

2. Embedded systems are not always standalone devices. Many embedded systems

consist of small, computerized parts within a larger device that serves a more general

purpose. For example, the Gibson Robot Guitar features an embedded system for

tuning the strings, but the overall purpose of the Robot Guitar is, of course, to play

music. Similarly, an embedded system in an automobile provides a specific function

as a subsystem of the car itself.

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3. The program instructions written for embedded systems are referred to as

firmware, and are stored in read-only memory or Flash memory chips. They run with

limited computer hardware resources: little memory, small or non-existent keyboard

and/or screen.

1.3 What’s a Microcontroller?

A microcontroller is a computer-on-a-chip or if we prefer a single-chip computer.

Micro suggests that the device is small, and controller tells that the device might be

used to control objects, processes or events. Another term to describe a

microcontroller isembedded controller, because the microcontroller and its support

circuits are often built into, or embedded in, the devices they control.

You can find microcontrollers in all kinds of things these days. Any device that

measures, stores, controls, calculates, or displays information is a candidate for

putting a microcontroller inside. The largest single use for microcontrollers is in

automobiles just about every car manufactured today includes at least one

microcontroller for engine control, and often more to control additional systems in

the car. In desktop computers, we can find microcontrollers inside keyboards,

modems, printers, and other peripherals. In test equipment, microcontrollers make it

easy to add features such as the ability to store measurements, to create and store

user routines, and to display messages and waveforms. Consumer products that use

microcontrollers include cameras, video recorders, compact-disk players, and ovens.

And these are just a few examples.

A microcontroller is similar to the microprocessor inside a personal computer. Both

microprocessors and microcontrollers contain a central processing unit, or CPU. The

CPU executes instructions that perform the basic logic, math, and data-moving

functions of a computer.

To make a complete computer, a microprocessor requires memory for storing data

and programs, and input/output (I/O) interfaces for connecting external devices like

keyboards and displays. In contrast, a microcontroller is a single-chip computer

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because it contains memory and I/O interfaces in addition to the CPU. Because the

amount of memory and interfaces that can fit on a single chip is limited,

microcontrollers tend to be used in smaller systems that require little more than the

microcontroller and a few support components. Examples of popular

microcontrollers are Intel’s 8051, Intel’s 8052, Motorola’s 68HC11, and Zilog’s Z8.

1.4 A Little History of Microcontroller

To understand how microcontrollers fit into the always-expanding world of

computers, we need to look back to the roots of micro computing.

Microcontrollers have gone through a silent evolution. The evolution can be rightly

termed as silent as the impact or application of a microcontroller is not well known to

a common user, although microcontroller technology has undergone significant

change since early 1970's.

Development of some popular microcontrollers is given as follows.

Intel 4004 4 bit (2300 PMOS trans, 108

kHz)

1971

Intel 8048 8 bit 1976

Intel 8031 8 bit (ROM-less) .

Intel 8051 8 bit (Mask ROM) 1980

Microchip PIC16C64 8 bit 1985

Motorola 68HC11 8 bit (on chip ADC) .

Intel 80C196 16 bit 1982

Atmel AT89C51 8 bit (Flash memory) .

Microchip PIC

16F877

8 bit (Flash memory + ADC) .

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1.5 User Interface And Peripherals

Embedded systems range from no user interface at all dedicated only to one task to

complex graphical user interfaces that resemble modern computer desktop operating

systems. Simple embedded devices use buttons, LEDs, graphic or character LCDs

(for example popular HD44780 LCD) with a simple menu system.

More sophisticated devices use graphical screen with touch sensing or screen-edge

buttons provide flexibility while minimizing space used: the meaning of the buttons

can change with the screen, and selection involves the natural behaviour of pointing

at what's desired. Handheld systems often have a screen with a "joystick button" for a

pointing device.

Some systems provide user interface remotely with the help of a serial (e.g. RS-232,

USB, etc.) or network (e.g. Ethernet) connection. In spite of the potentially necessary

proprietary client software and/or specialist cables that are needed, this approach

usually gives a lot of advantages: extends the capabilities of embedded system,

avoids the cost of a display, allows to build rich user interface on the PC. A good

example of this is the combination of an embedded web server running on an

embedded device (such as an IP camera) or a network routers.

Peripherals

Embedded Systems talk with the outside world via peripherals, such as:

– LED

– Displays: LCD, 7 segments etc.

– Serial Communication Interfaces (SCI): RS-232, RS-422, RS-485 etc.

– Synchronous Serial Communication Interface: I2C, SPI, SSC and ESSI (Enhanced

Synchronous Serial Interface)

– Universal Serial Bus (USB)

– Multi Media Cards (SD Cards, Compact Flash etc.)

– Networks: Ethernet, LonWorks, etc.

– Fieldbuses

– Timers: PLL(s), Capture/Compare and Time Processing Units

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– Discrete IO: aka General Purpose Input/Output (GPIO)

– Analog to Digital/Digital to Analog (ADC/DAC)

– Debugging: JTAG, ISP, ICSP, BDM Port, BITP, and DP9 ports.

1.6 Architecture of Microcontroller

At times, a microcontroller can have external memory also (if there is no internal memory or

extra memory interface is required). Early microcontrollers were manufactured using bipolar

or NMOS technologies. Most modern microcontrollers are manufactured with CMOS

technology, which leads to reduction in size and power loss. Current drawn by the IC is also

reduced considerably from 10mA to a few micro Amperes in sleep mode (for a

microcontroller running typically at a clock speed of 20MHz).

Fig 1.1 Internal Structure of a Microcontroller

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Chapter 2

Microcontroller 8051

2 .1 P in Diagram And Pin Funct ions

The pin diagram of the 8051 shows all of the input/output pins unique to

microcontrollers:

The following are some of the capabilities of 8051 microcontroller.

- Internal ROM and RAM

http://www.justsharehere.com/

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- I/O ports with programmable pins

- Timers and counters

-Serial data communication

ALE/PROG:

Address Latch Enable output pulse for latching the low byte of the address

during accesses to external memory.

ALE is emitted at a constant rate of 1/6 of the oscillator frequency, for

external timing or clocking purposes, even when there are no accesses to

external memory. (However, one ALE pulse is skipped during each access to

external Data Memory.)

This pin is also the program pulse input (PROG) during EPROM

programming.

PSEN:

Program Store Enable is the read strobe to external Program Memory.

When the device is executing out of external Program Memory, PSEN is

activated twice each machine cycle (except that two PSEN activations are

skipped during accesses to external Data Memory).

PSEN is not activated when the device is executing out of internal Program

Memory

EA/VPP:

When EA is held high the CPU executes out of internal Program.

Holding EA low forces the CPU to execute out of external memory

regardless of the Program Counter value.

In the EPROM devices, this pin also receives the programming supply

voltage (VPP) during EPROM programming.

XTAL1:

Input to the inverting oscillator amplifier.

XTAL2:

Output from the inverting oscillator amplifier.

Port 0:

Port 0 is an 8-bit bidirectional port.

As an open drain output port, it can sink eight LS TTL loads.

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Port 0 pins that have 1s written to them float, and in that state will function as

high impedance inputs.

Port 0 is also the multiplexed low-order address and data bus during accesses

to external memory.

In this application it uses strong internal pull-ups when emitting 1s.

Port 0 emits code bytes during program verification. In this application,

external pull-ups are required.

Port 1:

Port 1 is an 8-bit bidirectional I/O port with internal pull-ups.

Port 1 pins that have 1s written to them are pulled high by the internal pull-

ups, and in that state can be used as inputs.

As inputs, port 1 pins that are externally being pulled low will source current

because of the internal pull-ups.

Port 2:


Port 2 emits the high-order address byte during accesses to external memory

that use 16-bit addresses. In this application, it uses the strong internal pull-

ups when emitting 1s.

Port 3:


It also serves the functions of various special features of the 80C51 Family as

follows:

Port Pin Alternate Function

P3.0 RxD (serial input port)

P3.1 TxD (serial output port)

P3.2 INT0 (external interrupt 0)

P3.3 INT1 (external interrupt1)

P3.4 T0 (timer 0 external input)

P3.5 T1 (timer 1 external input )

P3.6 WR (external data memory write strobe)

P3.7 RD (external data memory read strobe)

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The alternate functions can only be activated if the corresponding bit latch in the port

SFR contains a 1. Otherwise the port pin remains at 0.

* All four ports in the 80C51 are bidirectional. Each consists of a latch (Special

Function Registers P0 through P3), an output driver, and an input buffer.

* The output drivers of Ports 0 and 2, and the input buffers of Port 0, are used in

accesses to external memory. In this application, Port 0 outputs the low byte of the

external memory address, time-multiplexed with the byte being written or read. Port

2 outputs the high byte of the external memory address when the address is 16 bits

wide. Otherwise, the Port 2 pins continue to emit the P2 SFR content.

Reset requirements

The process of starting any microcontroller is a non-trivial one. The underlying

hardware is complex and a small, manufacturer-defined, ‘reset routine’ must be run

to place this hardware into an appropriate state before it can begin executing the user

program. Running this reset routine takes time, and requires that the

microcontroller’s oscillator is operating.

Where your system is supplied by a robust power supply, which rapidly reaches its

specified output voltage when switched on, rapidly decreases to 0V when switched

off, and – while switched on – cannot ‘brown out’ (drop in voltage), then you can

safely use low-cost reset hardware based on a capacitor and a resistor to ensure that

your system will be reset correctly: this form of reset circuit is shown in Figure 2.3a.

Where your power supply is less than perfect, and / or your application is safety

related, the simple RC solution will not be suitable. Several manufacturers provide

more sophisticated reset chips which may be used in these circumstances

Clock frequency and performance

All digital computer systems are driven by some form of oscillator circuit: the 8051

is certainly no exception. The oscillator circuit is the ‘heartbeat’ of the system and is

crucial to correct operation. For example, if the oscillator fails, the system will not

function at all; if the oscillator runs irregularly, any timing calculations performed by

the system will be inaccurate.

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We consider some important issues linked to oscillator frequency and performance in

this section:

a) The link between oscillator frequency and machine-cycle period

One of the first questions to be asked when considering a microcontroller for a

project is whether it has the required level of performance. As a general rule, the

speed at which your application runs is directly determined by the oscillator

frequency: in most cases, if you double the oscillator frequency, the application will

run twice as fast. When we want to compare different processors, we need a way of

specifying performance in a quantitative manner. One popular measure is the number

of machine instructions that may be executed in one second, usually expressed in

‘MIPS’ (Million Instructions per Second). For example, in the original Intel 8051

microcontroller, a minimum of 12 oscillator cycles was required to execute a

machine instruction. The original 8051 had a maximum oscillator frequency of 12

MHz and therefore a peak performance of 1 MIP.

A simple way of improving the 8051 performance is to increase the clock frequency.

More modern (Standard) 8051 devices allow the use of clock speeds well beyond the

12 MHz limit of the original devices. For example, the Atmel AT89C55WD, allow

clock speeds up to 33 MHz: this raises the peak performance to around 3 MIPS.

Another way of improving the performance is to make internal changes to the

microcontroller so that fewer oscillator cycles are required to execute each machine

instruction. The Dallas ‘High Speed Microcontroller’ devices (87C520, and similar)

use this approach, so that only four oscillator cycles are required to execute a

machine instruction. These Dallas devices also allow faster clock rates (typically up

to 33 MHz). Combined, these changes give a total performance of around 8 MIPS.

Similar changes are made in members of the Winbond family of Standard 8051

devices (see the Winbond W77E58, for example) resulting in performance figures of

up to 10 MIPS.

Clearly, for maximum performance, we would like to execute instructions at a rate of

one machine instruction per oscillator cycle. For example, the Dallas ‘Ultra High

Speed’ 89C420 operates at this rate: as a result, it runs at 12 times the speed of the

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original 8051. In addition, the 89c420 can operate at up to 50 MHz, increasing

overall performance to around 40–50 MIPS.

To put all these figures in perspective, a modern desktop PC has a potential

performance of around 1000 MIPS. However, a good percentage of this performance

(perhaps 50% or more) will be ‘consumed’ by the operating system. By contrast, the

embedded operating system we will describe in Chapter 7 consumes less than 1% of

the processor resources of the most basic 8051: this leaves sufficient CPU cycles to

run a complex embedded application.

b) Why you should choose a low oscillator frequency

In our experience, many developers select an oscillator frequency that is at or near

the maximum value supported by a particular device. For example, the Infineon

C505/505C will operate with crystal frequency of 2–20 MHz, and many people

automatically choose values at or near the top of this range, in order to gain

maximum performance.

This can be a mistake, for the following reasons:- Many applications do not

require the levels of performance that a modern 8051 device canprovide.

- In most modern (CMOS-based) 8051s, there is an almost linear relationship

between the oscillator frequency and the power supply current. As a result, by using

the lowest frequency necessary it is possible to reduce the power requirement: this

can be useful, particularly in battery-powered applications.

- When accessing low-speed peripherals (such as slow memory, or liquid-crystal

displays), programming and hardware design can be greatly simplified – and the cost

of peripheral components, such as memory latches, can be reduced – if the chip is

operating more slowly.

- The electromagnetic interference (EMI) generated by a circuit increases with

clock frequency.

In general, you should operate at the lowest possible oscillator frequency compatible

with the performance needs of your application. As we will see in later chapters,

simulating the processor is a good way of determining the required operating

frequency for a particular application.

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Fig. Microcontroller

http://www.justsharehere.com/wp-content/uploads/2012/09/memory-Optimized.jpg

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Chapter 3

LED Interfacing

3.1 About LED

Discrete or individual LEDs (light-emitting diodes) are an easy way to indicate

status, such as On, Ready, Mode selected, and so on. They are colourful, eye-

catching, and easy to interface to 5-volt logic. Available colours now include blue as

well as red, green, and yellow. Some individual LED packages can emit red, green,

or amber light, depending on the voltages applied.

Like other diodes, current passes through an LED in one direction only. When a

positive voltage is applied to the anode, current flows and electrons migrate across an

energy gap in the LED, causing it to emit light. The size of the energy gap

determines the voltage drop across the LED, as well as the colour of light emitted. A

tinted case can also vary the colour.

Table 3. 1.The forward voltage drop across an LED varies with the colour.

LED colour typical forward voltage

(volts)

Red 1.6

Green 2.0

Yellow 2.0

Blue 3.2

Table 3.1 shows typical forward voltages for different colours of LEDs. Typical

LED operating currents are between 10 and 20 mill amperes. For a bright display

with low power consumption, look for types labelled high efficiency.

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One disadvantage to LEDs is that the light from most is hard to detect in bright light,

especially outdoors. A tinted, transparent sheet of plastic mounted over the display

can make it more visible in bright light. For red LEDs, transparent red or purple

works well.For best visibility over a wide area, look for LEDs with a wide viewing

angle. This means that the LED emits light in a wide cone, so you don’t need to view

it straight-on.

3.2 Bi-colour LEDs

Bi-colour LEDs have two LEDs of different colours inside a single package. By

turning on one, both, or neither, we can use a single indicator to show as many as

four states. Some bicolour LEDs have two leads, while others have three.

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Figure 3.2.Ways to connect bicolour LEDs.

Figure 3.2illustrates.

In the 3-lead, or common-cathode type, the cathodes of both LEDs connect internally

(A). To turn on an LED, we ground the cathodes through a current-limiting resistor

and apply power to the anode of the desired LED. When both LEDs are powered, we

get different light that is mixture of both led’s colour (amber in case of red and

green). Removing power from both turns the LED off, giving a total of four states

that the device can display. Instead of the one current-limiting resistor shown, we can

connect a resistor to each anode, to set the current through each LED individually.

In a 2-lead, or parallel-connected, bicolour LED, the anode of each LED connects

internally to the other’s cathode (B). To turn on the one LED, we apply +5V to

terminal A and ground terminal B. To turn on the other LED, we do the reverse

terminal A is ground and terminal B is +5V. With this type, we can’t turn on both

LEDs at once.With either type, by adding an inverter, we can use a single output to

control both LEDs (C, D).

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3.3 LED Interfacing

We can interface LED to any output port of 8051 microcontroller. When a LED is

connected to any circuit it usually takes 2 Volts (Red, Green) and a Blue or White

LED takes 4 Volts.

To turn on an LED at a port, write a 1 or 0, as appropriate, to the bit that controls it.

LED has two leads: Cathode and Anode. They are identified by the length of the lead.

Cathode is of broader filament.

Circuit diagram 3.1 LED interfacing

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Example

write a programme to show moving off in LEDs interfaced at port 2

Programme

01 #include<reg51.h> // Including header file

02 #define led P2 // Defining Port 2.0 as Led port

03 void delay(unsigned int);

04 void main() // Main function

05 {

06 while(1)

07 {

08 led=0xFF; //to on all the LEDs

09 delay(100); //delay function call

10 led=0x7F; // one led is off

11 delay(100);

12 led=0xBF;

13 delay(100);

14 led=0xDF;

15 delay(100);

16 led=0xEF;

17 delay(100);

18 led=0xF7;

19 delay(100);

20 led=0xFB;

21 delay(100);

22 led=0xFD;

23 delay(100);

24 led=0xFE;

25 delay(100);

26 }

27 }

28 void delay(unsigned int e)

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29 { unsigned inti,j;

30 for(i=0;i<e;i++)

31 for(j=0;j<1275;j++);

32 }

Circuit diagram 3.2

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Chapter 4

7 segment display interfacing

4.1 7-segment Displays

If we want to display numbers, 7-segment displays will do the job. Each digit on the

display contains seven segments. Numerals are displayed by turning on different

combinations of segments, as Figure 4.1 shows.

Figure 4.1A 7-segment display can show numbers from 0 to 9 and hex digits A-F.

Decoder chips make it easy to operate one or more displays with a minimum of

programming and added components. Seven-segment displays are available as LEDs,

where each segment is a light-emitting diode, and as LCDs, where each segment is a

liquid-crystal display. We’ll look at the LED type first.

4.2 7-segment LEDs

A 7-segment LED contains seven individual LEDs arranged in the pattern shown in

Figure 4.2 Sometimes there is also a decimal point (or two, one on each side). There

are also special leading-digit modules that display only a 1 and a plus-or-minus

symbol.

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The displays come in two types: common-anode or common-cathode. In a common-

anode display, the anodes of each segment connect internally. To use the display,

you connect the anodes to a voltage source and turn on individual segments by

grounding them through a current-limiting resistor. A common-cathode display is the

opposite: the cathodes connect internally, so you ground the cathodes and apply

voltages through current-limiting resistors at the segments you want to light.

Figure 4.2 7-segment LEDs

4.3 7-segment LCDs

An alternative to LEDs is liquid-crystal displays (LCDs). Unlike LEDs, which

consume several milliamperes per segment, LCDs are voltage-controlled and require

very little operating current.

Compared to LEDs, LCDs are easy to read in bright light. However, because LCDs

don’t emit light as LEDs do, but merely absorb or transmit it, we need additional

lighting to see them in the dark. LCDs also tend to have narrower viewing angles

than LEDs. So, whether to use LEDs or LCDs may depend on where and how we

will use the display.

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Most 7-segment LCD modules contain two or more digits. Like the LEDs, a 7-

segment LCD creates a numeral by turning on selected segments.

Each LCD segment contains a thin layer of liquid crystal between two layers of

glass. Liquid crystals are organic compounds that act as electrically controlled light

polarizers. In a positive-image display (the most common type), applying a voltage

across a segment causes the segment to appear dark, or opaque, while removing the

voltage causes the segment to appear light-colored, or transparent. Negative-image

displays are opaque when not powered, and transparent when powered. By applying

and removing voltages across individual segments, you can display numeric,

alphabetic, and other characters.

Applying a constant voltage to an LCD segment will eventually destroy it. Instead,

you must drive the segment with an alternating voltage, typically a square wave that

alternately applies +5 and -5V across the segment.

4.4 7 segment display interfacing

There isn’t much standardization for pinouts of 7-segment displays. If we don’t know

the pinout for a display, we can find it by experimenting. We’ll need a 330-ohm

resistor and a 5-volt supply.

Sometimes we’ll find CC or CA stamped on the package to indicate common cathode

or common anode. If even this information is lacking, begin by connecting one lead

of the resistor to ground on your power supply. Clip the resistor’s other end to one of

the LED’s pins. Use a test lead to touch the power supply +5V output to each of the

other pins in turn.

If only one or two connections cause a segment to light, you have a common-anode

display, and the common anode is the pin or pins that connect to +5V when the

segment lights. (There may be two common-anode pins.) To find the pin that

controls each segment, leave the +5V lead on a common-anode pin, and connect the

resistor to each pin in turn, noting the results.

For a common-cathode display, to find the common-cathode pin or pins, connect a

pin to +5V, and touch the others to ground through the 330-ohm resistor. The pin or

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pins that cause the segment to light are the common-cathode connections. To find the

pin that controls each segment, move the +5V lead to each pin in turn, and note the

results.

Figure 4.3

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Circuit diagram 4.1 for 7 segment display interfacing with 8051uc

Examples

1. Write a programme to design a up down counter using 8051 with 7

segment interfacing.

01 #include <REGX51.H>


03 unsigned char z[]={0xC0,0xF9,0xA4,0xB0,0x99, 0x92, 0x82,

0xF8,0x80,0x90};

04 sbit up = P2^0;

05 sbit down=P2^1;

06 void main()

07 { while(1)

08 {unsigned inti;

09 if( up==0 && down==1)

10 {if(i>=9)

11 { i==0;

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12 }else

13 { i++;

14 P3=z[i];

15 delay(100);

16 }}

17 else if( up== 1 && down==0)

18 {if(i<=0)

19 {i==0;

20 }else

21 {i--;

22 P3=z[i];

23 delay(100);

24 }}} }

25 void delay(unsigned int x)

26 {unsigned inta,b;

27 for(a=0;a<x;a++)

28 for(b=0;b<1275;b++);

29 }

Circuit diagram

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2. Design an interfacing to make a free running counter up to 9999.



03 void display(unsigned int);

04 sbit s4=P3^0;

05 sbit s3=P3^1;

06 sbit s2=P3^2;

07 sbit s1=P3^3;

08 void main()

09 { unsigned inta,b,c,d,e,f;

10 unsigned int count;

11 while(1)

12 {s4=s3=s2=s1=0;

13 for(count =00;count<=9999;count++)

14 {a=count%100;

15 b=count/100;

16 c=a%10;

17 d=a/10;

18 e=b%10;

19 f=b/10;

20 s1=1;

21 s3=s2=s4=0;

22 display(c) ;

23 delay(1);

24 s1=0;

25 s2=1;

26 s3=s4=0;

27 display(d);

28 delay(3);

29 s2=0;

30 s3=1;

31 s4=s1=0;

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32 display(e);

33 delay(3);

34 s3=0;

35 s4=1;

36 s2=s1=0;

37 display(f);

38 delay(5);

39 }}}

40 void display(unsigned int x)

41 {unsigned int y;

42 y=x;

43 switch(y)

44 {case 0:

45 P2 =0xC0;

46 break;

47 case 1:

48 P2 =0xF9;

49 break;

50 case 2:

51 P2 =0xA4;

52 break;

53 case 3:

54 P2 =0xB0;

55 break;

56 case 4:

57 P2 =0x99;

58 break;

59 case 5:

60 P2 =0x92;

61 break;

62 case 6:

63 P2 =0x82;

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64 break;

65 case 7:

66 P2 =0xF8;

67 break;

68 case 8:

69 P2 =0x80;

70 break;

71 case 9:

72 P2 =0x90;

73 break;

74 }}

75 void delay(unsigned int a)

76 { unsigned intb,c;

77 for (b =0;b<a;b++)

78 for (c=0;c<1275;c++);

79 }

Circuit diagram

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Chapter 5

LCD interfacing

5.1 About LCD

Sometimes a device has to display more complex messages than simple LEDs and 7-

segment displays can handle. For example, you might want to display messages like

these:

Please enter your access code.

Select function:

Read

Program

Verify

Exit

Wind is from the west at 12 mph

Total cost = $5.82

Room temperature is 26c

We can use the host computer’s display, but this is no help if you want to create a

stand-alone project that doesn’t require a personal computer. In these situations, a

character-based dot-matrix LCD module is a solution.

These modules can display messages made up of numbers, characters of the

alphabet, and other symbols (for math functions, for example, or even symbols you

design yourself). Figure 5.1 illustrates. Devices that use this type of display include

laser printers and test equipment.

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Figure 5.1With a character-based dot-matrix LCD module, you can display

messages as well as numbers.

5.2 About the Modules

The character-based LCD modules are available from many companies, including

Philips, Optrex, and Densitron. Complete technical information on the controller and

displays is available from Hitachi and the display manufacturers, and from some

distributors and catalogs.

The display of one of these modules contains one or more rows of character

positions. Each character position consists of a matrix that is typically five segments,

or dots, wide and eight segments tall. (The HD44780 can also control matrices that

are 11 segments tall, for better display of characters with descenders, like g, p, and

q.)

The module forms characters by turning on the appropriate segments in a character

position. For example, to display an L, the module turns on one vertical column

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andone horizontal row of segments. For most characters, the bottom row is reserved

for displaying a cursor, which leaves 35 segments to form the character.

Displays are available in several sizes. Popular sizes are 1 x 16 (1 line of 16

characters), 2 x 16, and 2 x 20. Displays larger than 80 characters require

supplemental driver chips along with the HD44780, but the displays can use the

same interface.

Table 5.1 summarizes the signals in the 14-line interface.

Pin

Symbol Input/

Output

Function

1 VSS Input Signal Ground

2 VDD Input Supply Voltage (+5V)

3 V0 Input Contrast adjust

4 RS Input Register select (1=data; 0=instruction

register, busy flag/address counter)

5 R/W Input Read (1)/write (0) select

6 E Input Enable

7 D0 I/O Data bit 0

8 D1 I/O Data bit 1

9 D2 I/O Data bit 2

10 D3 I/O Data bit 3





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Figure 5.2 2*16 LCD

5.3 Power Supplies and Backlights

The power supply (pin 2) is a simple +5V DC. The modules contain their own

oscillators to drive the LCD segments. Typical power consumption for an entire

module is just a couple of milliamperes. A contrast input (pin 3) allows you to adjust

for best viewing under varying light conditions, viewing angles, and temperatures.

Some LCD modules use backlighting to allow viewing in dim light. A module may

be reflective (which does not use backlighting), transmissive (which must use

backlighting), or transflective (which may use backlighting or not). With a

transflective display, you can add a switch to enable users to turn the backlighting on

or off as desired.

One popular type of backlight is an electroluminescence (EL) panel behind the LCD

segments. An EL panel emits a diffuse light that provides a bright background for the

LCDs. Electroluminescent backlighting requires first of all, a module that contains an

EL panel, and second, an inverter module to provide the high-voltage alternating

signal required to power the panel. The inverters typically convert +5 volts to around

100 volts RMS at 400 Hertz. Inverters are usually offered along with the modules

that use them, so you shouldn’t have to construct your own. The backlighting

requires several milliamperes. Incandescent and LED backlights are other options for

illuminating LCDs.

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5.4 Reading and Writing

Writing to the LCD module involves the following steps:

Bring RS high to write data, or low to write an instruction.

Bring R/W low.

Bring D0-D7 to their desired states.

Wait at least 140 nanoseconds.

Bring E high for at least 450 nanoseconds.

Bring E low.

Read operations are similar to writes, with R/W high instead of low. The data appears

on D0-D7 in 320 nanoseconds or less after E goes high.

5.5 LCD Interfacing

On the LCD module, pins 1-3 connect to ground, +5V, and a contrast potentiometer.

For maximum contrast, connect pin 3 directly to ground. Pins 4-6 are the control

signals for the LCD module. These connect to three outputs on Port C. The eight data

bits, pins 7-14 on the LCD module, connect to any Port .

Initializing the module. On power up, the LCD module must initialize properly.

If power-up is clean, with the supply voltage rising from 0.2V to 4.5V in 10

milliseconds or less, the module initializes automatically. But, if power-up doesn’t

meet this requirement, your program has to provide the initialization routine. It’s a

good idea to always include an initialization routine in your program, since it does no

harm, and if the module doesn’t initialize properly, it won’t respond correctly or at

all. Table 8-3 summarizes the initialization procedure. In short, the module must first

receive three identical commands selecting an 8-bit interface. To begin the

initializing, you must send the instruction to select an 8-bit interface, even if your

interface is four bits.

Initialization procedure for LCD modules using HD44780 Controller

Power on

Wait 15 milliseconds after V+ = 4.5V

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Function set = 30h

Wait 4.1 milliseconds

Function set = 30h

Wait 100 microseconds

Function set = 30h

Function set to match display module

Display on

Display clear

Entry mode set

Example

Write a program to print the text WELCOME on LCD interfaced to uc 8051.


02 #define lcd P3

03 sbitrs = P2^5;

04 sbitrw = P2^6;

05 sbit en = P2^7;

06 void lcd_cmd(unsigned char);

07 void lcd_data(unsigned char);


09 void main()

10 {

11 while(1)

12 {

13 lcd_cmd(0x38);

14 delay(1);

15 lcd_cmd(0x80);

16 delay(1);

17 lcd_cmd(0x0e);

18 delay(1);

19 lcd_data('m');

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20 delay(1);

21 lcd_data('a');

22 delay(1);

23 lcd_data('a');

24 delay(1);

25 }

26 }

27 void lcd_cmd(unsigned char c)

28 {

29 lcd=c;

30 rs=0;

31 rw=0;

32 en=1;

33 delay(1);

34 en=0;

35 }

36 void lcd_data(unsigned char d)

37 {

38 lcd=d;

39 rs=1;

40 rw=0;

41 en=1;

42 delay(1);

43 en=0;

44 }

45 void delay(unsigned int x)

46 {

47 unsigned inti,j;

48 for(i=0;i<x;i++)

49 for(j=0;j<1275;j++);

50 }

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Circuit diagram

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Reference

http://www.wikipedia.org/wiki/Liquid_crystal_display

http://www.wikipedia.org/wiki/7_segment_display

8051 microcontroller By Mazidi and Mazidi

http://www.wikipedia.org/wiki/Liquid_crystal_display

http://www.wikipedia.org/wiki/7_segment_display

EMBEDDED SYSTEM

Engineering

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