vehicletrackingsystemusinggpsandgsmtechniques-140416102026-phpapp02.pdf

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A

Major Project Report

On

Vehicle Tracking System using GSM and GPS

Submitted in partial fulfillment of the requirement for the degree of

BACHELOR OF TECHNOLOGY In

ELECTRONICS & COMMUNICATION ENGINEERING

Submitted by

CH. Bharath. 107B1A0435

P. Vijay Kumar. 107B1A0437

P. Anil Reddy. 107B1A0449

B. Abhishek. 107B1A0468

Under the Esteemed Guidance of

Mr. B. SRINIVASM. Tech, MISTE, AMIE, (Ph.D)

Ass i s t an t P ro fes sor

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

SAGAR INSTITUTE OF TECHNOLOGY (SITECH)

SAGAR GROUP OF INSTITUTIONS(Affiliated to JNTU Hyderabad and Approved by AICTE, New Delhi)

Flame of Forest, Urella-Chevella Road, Chevella, RR District

(2010-2014)


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Certificate

This is to certify that this dissertation work entitled “Vehicle Tracking System using GSM

and GPS” is a bonafide work carried out by CH. Bharath (107B1A0435), P. Vijay Kumar

(107B1A0437), P. Anil Reddy (107B1A0449) and B. Abhishek (107B1A0468) in partial

fulfillment of the requirements for the award of the degree of Bachelor of Technology in

Electronics and Communication Engineering, from “Sagar Institute of Technology”, during the period 2013 under the guidance and supervision.

Head of the Department

Prof. V. Bhagya Raju

M. Tech, (Ph.D.)

Professor & HOD of ECE.

Internal Guide

Mr. B. SRINIVAS

M. Tech, MISTE, AMIE, (Ph.D.)

Ass i s t an t P ro fes sor

Depar tment o f E CE

External Examiner

SAGAR GROUP OF INSTITUTINSSAGAR INSTITUTE OF TECHNOLOGY

(Affiliated to JNTU Hyderabad and Approved by AICTE, New Delhi)

Flame of Forest, Urella- Chevella Road, Chevella, RR Dist.


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DECLARATION

We hereby declare that the project “Vehicle Tracking System using GSM and GPS”

submitted in the partial fulfilment of that requirements for the award of the degree of

bachelor of technology in electronics and communication engineering from Sagar

Institute Of Engineering and Technology, Chevella, affiliated to JNTU, Hyderabad is an

authentic work and has not been submitted to any other university/institute for award of

degree.

CH. Bharath (107B1A0435)

P. Vijay Kumar (107B1A0437)

P. Anil Reddy (107B1A0449)

B. Abhishek (107B1A0468)

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ACKNOWLEDGEMENT

With great pleasure we want to take this opportunity to express our heartfelt gratitude

to all the people who helped in making this Major Project work a grand success.

We are grateful to Prof.V.Bhagya Raju, Professor & Head of Electronics andCommunication Engineering department, Mr. B. Srinivas, Asst. Prof. Dept of ECE and P.

Tejaswi Project Assistant at ECIL for their valuable suggestions and guidance during the

execution of this project and also for giving us moral support throughout the period of our

study in SITECH.

We are also highly indebted to our principal Dr. V.V. Satyanarayana, for giving

us the permission to carry out this Major Project.

We would like to thank the teaching and non-teaching staff of ECE Department for sharing

their knowledge with us.

Last but not the least we express our sincere thanks to Dr.W.R.Reddy and all the

founders of Sagar Institute of Technology for their continuous care towards our

achievements.

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Index

Declaration i

Acknowledgement ii

Index iii

List of Figures viii

List of Tables ix

Abbreviations x

Chapter 1: Introduction To VTS 1

1.1 Introduction 1

1.2 Vehicle Security using VTS 2

1.3 Active versus Passive Tracking 4

1.4 Types of GPS Vehicle Tracking 5

1.5 Typical Architecture 6

1.6 History of Vehicle Tracking 7

1.6.1 Early Technology 8

1.6.2 New development in technology 9

1.7 Vehicle Tracking System Features 9

1.7.1 Vehicle Tracking Benefits 10

1.8 Vehicle Tracing in India 10

Chapter 2: Block Diagram of VTS 12

2.1 Block Diagram of Vehicle Tracing Using GSM and GPS Modem

2.2 Hardware Components

2.2.1 GPS 13

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2.2.1.1 Working of GPS 13

2.2.1.2 Triangulation 14

2.2.1.3 Augmentation 14

2.2.2 GSM 15

2.2.3 RS232 Interface 16

2.2.3.1 The scope of the standard 16

2.2.3.2 History of RS 232 17

2.2.3.3 Limitation of Standard 18

2.2.3.4 Standard details 19

2.2.3.5 Connectors 21

2.2.3.6 Cables 24

2.2.3.7 Conventions 24

2.2.3.8 RTS/CTS handshaking 25

2.2.3.9 3-wire and 5-wire RS-232 26

2.2.3.10 Seldom used features 26

2.2.3.11 Timing Signals 27

2.2.3.12 Other Serial interfaces similar to RS-232 27

2.2.4 MAX232 IC 28

2.2.4.1 Voltage Levels 29

2.2.4.2 Pin Diagram 30

2.2.4.3 Pin Description 31

2.2.5 Relay 31

2.2.5.1 History of a Relay 32

2.2.5.2 Basic Design and Operation of a Relay 33

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2.2.5.3 Pole and Throw 34

2.2.5.4 Uses of Relays 35

2.2.6 LCD 35

2.2.6.1 Advantages and Disadvantages 36

Chapter 3: Working of VTS 37

3.1 Schematic Diagram of VTS 37

3.2 Circuit Description 37

3.3 Circuit Operation 38

3.3.1 Power 38

3.3.2 Serial Ports 38

3.4 Operating procedure 38

Chapter 4: Microcontroller AT 89S52 40

4.1 Features 40

4.2 The Pin Configuration 41

4.2.1 Special Function Registers (SFR) 42

4.3 Memory Organization 43

4.4 Watch Dog Timer 43

4.4.1 Watchdog Timer for both modes of operation 44

Chapter 5: GSM Module 46

5.1 GSM History 46

5.2 Services Provided by GSM 47

5.3 Mobile Station 48

5.4 Base Station Subsystem 50

5.4.1 Base Station Controller 51

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5.5 Architecture of the GSM Network 52

5.6 Radio Link Aspects 53

5.7 Multiple Access and Channel Structure 54

5.8 Frequency Hopping 54

5.9 Discontinuous Reception 55

5.10 Power Control 55

5.11 Network Aspects 56

5.12 Radio Resources Management 57

5.13 Handover 57

5.14 Mobility Management 59

5.15 Location Updating 59

5.16 Authentication and Security 60

5.17 Communication Management 61

5.18 Call Routing 61

Chapter 6: GPS Receiver 63

6.1 GPS History 63

6.1.1 Working and Operation 64

6.2 GPS Data Decoding 65

Chapter 7: KEIL Software 67

7.1 Introduction 67

7.2 KEIL uVision2 66

7.3 KEIL Software Programing Procedure 67

7.3.1 Procedure Steps 67

7.4 Applications of KEIL Software 69

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Chapter 8: Applications 70

8.1 Applications 71

8.2 Limitations 72

Chapter 9: Result Analysis 73

Chapter 10: Conclusion and Future Scope 75

References 76

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List of Figures

Figure 1.1 Vehicle tracking system 2

Figure 2.1 Block diagram 12

Figure 2.2

A 25 pin connector as described in the RS-232 standard 16

Figure 2.3 Trace of voltage levels for uppercase ASCII "K" character 19

Figure 2.4 Upper Picture: RS232 signaling as seen when probed by an actual

oscilloscope

20

Figure 2.5 MAX232 chip 28

Figure 2.6 Pin diagram of MAX232 30

Figure 2.7

UK Q-style signaling relay and base. 32

Figure 2.8 Automotive-style miniature relay, dust cover is taken off 32

Figure 2.9 Circuit symbols of relays. 34

Figure 2.10 A general purpose alphanumeric LCD, with two lines of 16

characters.

35

Figure 3.1 Schematic diagram of vehicle tracing using GSM and GPS 37

Figure 5.1 Mobile station SIM port 49

Figure 5.2 Baste Station Subsystem. 50

Figure 5.3 Siemens BSC 51

Figure 5.4 Siemens’ TRAU 52

Figure 5.5 General architecture of a GSM network 53

Figure 5.6 Signaling protocol structure in GSM 57

Figure 5.7 Call routing for a mobile terminating call 61

Figure 6.1 G.P.S receiver communicating with the satellite 65

Figure 9.1 Picture of final VTS kit 73

Figure 9.2 Message received from the VTS kit 74

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List of Tables

Table 2.1 Commonly used RS-232 signals and pin assignments 22

Table 2.2

Pin assignments 23

Table 2.3 RS-232 Voltage Levels 29

Table 2.4 TX and RX pin connection 30

Table 2.5 Pins assignment of MAX232 30

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Abbreviations

VTS Vehicle Tracking System

GSM Global System for Mobile Communication

GPS Global Positioning System

RI Ring Indicator

Tx Transmitter

Rx Receiver

SFR Special Function Register

LCD Liquid Crystal Display

RAM Random Access Memory

ROM Read Only Memory

RS-232 Recommended Standard

TTL Transistor Transistor Logic

CMOS Complementary Metal Oxide Semi-Conductor

UART Universal Asynchronous Receiver Transmitter

RST Reset

ALE Address Latch Enable

PSEN Program Store Enable

WDT Watch Dog Timer

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Chapter 1

Introduction to VTS

1.1 Introduction

Vehicle Tracking System (VTS) is the technology used to determine the location

of a vehicle using different methods like GPS and other radio navigation systems

operating through satellites and ground based stations. By following triangulation or

trilateration methods the tracking system enables to calculate easy and accurate location

of the vehicle. Vehicle information like location details, speed, distance traveled etc. can

be viewed on a digital mapping with the help of a software via Internet. Even data can be

stored and downloaded to a computer from the GPS unit at a base station and that can

later be used for analysis. This system is an important tool for tracking each vehicle at a

given period of time and now it is becoming increasingly popular for people having

expensive cars and hence as a theft prevention and retrieval device.

i.

The system consists of modern hardware and software components enabling one

to track their vehicle online or offline. Any vehicle tracking system consists of

mainly three parts mobile vehicle unit, fixed based station and, database and

software system.

ii.

Vehicle Unit: It is the hardware component attached to the vehicle having either a

GPS/GSM modem. The unit is configured around a primary modem that functions

with the tracking software by receiving signals from GPS satellites or radio station

points with the help of antenna. The controller modem converts the data and sends

the vehicle location data to the server.

iii. Fixed Based Station: Consists of a wireless network to receive and forward the

data to the data center. Base stations are equipped with tracking software and

geographic map useful for determining the vehicle location. Maps of every cityand landmarks are available in the based station that has an in-built Web Server.

iv. Database and Software: The position information or the coordinates of each

visiting points are stored in a database, which later can be viewed in a display

screen using digital maps. However, the users have to connect themselves to the

web server with the respective vehicle ID stored in the database and only then s/he

can view the location of vehicle traveled.

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1.2 Vehicle Security using VTS

Vehicle Security is a primary concern for all vehicle owners. Owners as well as

researchers are always on the lookout for new and improved security systems for their

vehicles. One has to be thankful for the upcoming technologies, like GPS systems, whichenables the owner to closely monitor and track his vehicle in real-time and also check the

history of vehicles movements. This new technology, popularly called Vehicle Tracking

Systems has done wonders in maintaining the security of the vehicle tracking system is

one of the biggest technological advancements to track the activities of the vehicle. The

security system uses Global Positioning System GPS, to find the location of the

monitored or tracked vehicle and then uses satellite or radio systems to send to send the

coordinates and the location data to the monitoring center. At monitoring center various

software’s are used to plot the Vehicle on a map. In this way the Vehicle owners are able

to track their vehicle on a real-time basis. Due to real-time tracking facility, vehicle

tracking systems are becoming increasingly popular among owners of expensive vehicles.

Figure 1.1 Vehicle tracking system

The vehicle tracking hardware is fitted on to the vehicle. It is fitted in such a manner

that it is not visible to anyone who is outside the vehicle. Thus it operates as a covert unit

which continuously sends the location data to the monitoring unit.When the vehicle is stolen, the location data sent by tracking unit can be used to

find the location and coordinates can be sent to police for further action. Some Vehicle

tracking System can even detect unauthorized movements of the vehicle and then alert the

owner. This gives an edge over other pieces of technology for the same purpose

Monitoring center Software helps the vehicle owner with a view of the location at

which the vehicle stands. Browsing is easy and the owners can make use of any

browser and connect to the monitoring center software, to find and track his vehicle. This

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in turn saves a lot of effort to find the vehicle's position by replacing the manual call to

the driver.

As we have seen the vehicle tracking system is an exciting piece of technology for

vehicle security. It enables the owner to virtually keep an eye on his vehicle any time and

from anywhere in the world.

A vehicle tracking system combines the installation of an electronic device in a

vehicle, or fleet of vehicles, with purpose-designed computer software at least at one

operational base to enable the owner or a third party to track the vehicle's location,

collecting data in the process from the field and deliver it to the base of operation.

Modern vehicle tracking systems commonly use GPS or GLONASS technology for

locating the vehicle, but other types of automatic vehicle location technology can also be

used. Vehicle information can be viewed on electronic maps via the Internet or

specialized software. Urban public transit authorities are an increasingly common user of

vehicle tracking systems, particularly in large cities.

Vehicle tracking systems are commonly used by fleet operators for fleet

management functions such as fleet tracking, routing, dispatch, on-board information and

security. Along with commercial fleet operators, urban transit agencies use the

technology for a number of purposes, including monitoring schedule adherence of buses

in service, triggering changes of buses' destination sign displays at the end of the line (or

other set location along a bus route), and triggering pre-recorded announcements for

passengers. The American Public Transportation Association estimated that, at the

beginning of 2009, around half of all transit buses in the United States were already using

a GPS-based vehicle tracking system to trigger automated stop announcements. This can

refer to external announcements (triggered by the opening of the bus's door) at a bus stop,

announcing the vehicle's route number and destination, primarily for the benefit

of visually impaired customers, or to internal announcements (to passengers already on

board) identifying the next stop, as the bus (or tram) approaches a stop, or both. Data

collected as a transit vehicle follows its route is often continuously fed into a computer

program which compares the vehicle's actual location and time with its schedule, and in

turn produces a frequently updating display for the driver, telling him/her how early or

late he/she is at any given time, potentially making it easier to adhere more closely to the

published schedule. Such programs are also used to provide customers with real-time

information as to the waiting time until arrival of the next bus or tram/streetcar at a given

stop, based on the nearest vehicles' actual progress at the time, rather than merely giving

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information as to the scheduled time of the next arrival. Transit systems providing this

kind of information assign a unique number to each stop, and waiting passengers can

obtain information by entering the stop number into an automated telephone system or an

application on the transit system's website. Some transit agencies provide a virtual map

on their website, with icons depicting the current locations of buses in service on each

route, for customers' information, while others provide such information only to

dispatchers or other employees.

Other applications include monitoring driving behavior, such as an employer of an

employee, or a parent with a teen driver.

Vehicle tracking systems are also popular in consumer vehicles as a theft prevention

and retrieval device. Police can simply follow the signal emitted by the tracking system

and locate the stolen vehicle. When used as a security system, a Vehicle Tracking System

may serve as either an addition to or replacement for a traditional car alarm. Some vehicle

tracking systems make it possible to control vehicle remotely, including block doors or

engine in case of emergency. The existence of vehicle tracking device then can be used to

reduce the insurance cost, because the loss-risk of the vehicle drops significantly.

Vehicle tracking systems are an integrated part of the "layered approach" to vehicle

protection, recommended by the National Insurance Crime Bureau (NICB) to

prevent motor vehicle theft. This approach recommends four layers of security based on

the risk factors pertaining to a specific vehicle. Vehicle Tracking Systems are one such

layer, and are described by the NICB as “very effective” in helping police recover stolen

vehicles.

Some vehicle tracking systems integrate several security systems, for example by

sending an automatic alert to a phone or email if an alarm is triggered or the vehicle is

moved without authorization, or when it leaves or enters a geofence.

1.3 Active versus Passive Tracking

Several types of vehicle tracking devices exist. Typically they are classified as

"passive" and "active". "Passive" devices store GPS location, speed, heading and

sometimes a trigger event such as key on/off, door open/closed. Once the vehicle returns

to a predetermined point, the device is removed and the data downloaded to a computer

for evaluation. Passive systems include auto download type that transfer data via wireless

download. "Active" devices also collect the same information but usually transmit the

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data in real-time via cellular or satellite networks to a computer or data center for

evaluation.

Many modern vehicle tracking devices combine both active and passive tracking

abilities: when a cellular network is available and a tracking device is connected it

transmits data to a server; when a network is not available the device stores data in

internal memory and will transmit stored data to the server later when the network

becomes available again.

Historically vehicle tracking has been accomplished by installing a box into the

vehicle, either self-powered with a battery or wired into the vehicle's power system. For

detailed vehicle locating and tracking this is still the predominant method; however, many

companies are increasingly interested in the emerging cell phone technologies that

provide tracking of multiple entities, such as both a salesperson and their vehicle. These

systems also offer tracking of calls, texts, and Web use and generally provide a wider

range of options.

1.4 Types of GPS Vehicle Tracking

There are three main types of GPS vehicle tracking, tracking based mobile, wireless

passive tracking and satellite in real-time GPS tracking. This article discusses the

advantages and disadvantages to all three types of GPS vehicle tracking circumference.

i) Mobile phone based tracking

The initial cost for the construction of the system is slightly lower than the other two

options. With a mobile phone-based tracking average price is about $ 500. A cell-

based monitoring system sends information about when a vehicle is every five minutes

during a rural network. The average monthly cost is about thirty-five dollars for airtime.

ii)

Wireless Passive Tracking

A big advantage that this type of tracking system is that there is no monthly fee, so

that when the system was introduced, there will be other costs associated with it. But

setting the scheme is a bit 'expensive. The average is about $ 700 for hardware and $ 800

for software and databases. With this type of system, most say that the disadvantage is

that information about where the vehicle is not only can exist when the vehicle is returned

to the base business. This is a great disadvantage, particularly for companies that are

looking for a monitoring system that tells them where their vehicle will be in case of theft

or an accident. However, many systems are now introducing wireless modems into their

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devices so that tracking information can be without memory of the vehicle to be seen.

With a wireless modem that is wireless passive tracking systems are also able to gather

information on how fast the vehicle was traveling, stopping, and made other detailed

information. With this new addition, many companies believe that this system is perfect,

because there is no monthly bill.

iii) Via satellite in real time

This type of system provides less detailed information, but work at the national

level, making it a good choice for shipping and trucking companies. Spending on

construction of the system on average about $ 700. The monthly fees for this system vary

from five dollars for a hundred dollars, depending on how the implementation of a

reporting entity would be.

Technology

Over the next few years, GPS tracking will be able to provide businesses with a

number of other benefits. Some companies have already introduced a way for a customer

has signed the credit card and managed at local level through the device. Others are

creating ways for dispatcher to send the information re-routing, the GPS device directly to

a manager. Not a new requirement for GPS systems is that they will have access to the

Internet and store information about the vehicle as a driver or mechanic GPS device to

see the diagrams used to assist with the vehicle you want to leave. Beyond that all the

information be saved and stored in its database.

1.5 Typical Architecture

Major constituents of the GPS based tracking are

i. GPS tracking device

The device fits into the vehicle and captures the GPS location information apart

from other vehicle information at regular intervals to a central server. The other

vehicle information can include fuel amount, engine temperature, altitude, reverse

geocoding, door open/close, tire pressure, cut off fuel, turn off ignition, turn on

headlight, turn on taillight, battery status, GSM area code/cell code decoded,

number of GPS satellites in view, glass open/close, fuel amount, emergency

button status, cumulative idling, computed odometer, engine

RPM, throttle position, and a lot more. Capability of these devices actually

decides the final capability of the whole tracking system.

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ii. GPS tracking server

The tracking server has three responsibilities: receiving data from the GPS

tracking unit, securely storing it, and serving this information on demand to the

user.iii. User interface

The UI determines how one will be able to access information, view vehicle data,

and elicit important details from it.

1.6 History of Vehicle Tracking

GPS or Global Positioning Systems were designed by the United States Government

and military, which the design was intended to be used as surveillance. After several

years went by the government signed a treaty to allow civilians to buy GPS units also

only the civilians would get precise downgraded ratings.

Years after the Global Positioning Systems were developed the military controlled

the systems despite that civilians could still purchase them in stores. In addition, despite

that Europe has designed its own systems called the Galileo the US military still has

complete control.

GPS units are also called tracking devices that are quite costly still. As more of

these devices develop however the more affordable the GPS can be purchased. Despite of

the innovative technology and designs of the GPS today the devices has seen some

notable changes or reductions in pricing. Companies now have more access to these

devices and many of the companies can find benefits.

These days you can pay-as-you go or lease a GPS system for your company. This

means you do not have to worry about spending upfront money, which once stopped

companies from installing the Global positioning systems at one time.

Today’s GPS applications have vastly developed as well. It is possible to use the

Global Positioning Systems to design expense reports, create time sheets, or reduce the

costs of fuel consumption. You can also use the tracking devices to increase efficiency of

employee driving. The GPS unit allows you to create Geo-Fences about a designated

location, which gives you alerts once your driver(s) passes through. This means you have

added security combined with more powerful customer support for your workers.

Today’s GPS units are great tracking devices that help fleet managers stay in control

of their business. The applications in today’s GPS units make it possible to take full

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control of your company. It is clear that the tracking devices offer many benefits to

companies, since you can build automated expense reports anytime.

GPS units do more than just allow companies to create reports. These devices also

help to put an end to thieves. According to recent reports, crime is at a high, which means

that car theft is increasing. If you have the right GPS unit, you can put an end to car thefts

because you can lock and unlock your car anytime you choose.

GPS are small tracking devices that are installed in your car and it will supply you

with feedback data from tracking software that loads from a satellite. This gives you more

control over your vehicles.

The chief reason for companies to install tracking devices is to monitor their mobile

workforce. A preventive measure device allows companies to monitor their employees’

activities. Company workers can no longer take your vehicles to unassigned locations.

They will not be able to get away with unauthorized activities at any time because you

can monitor their every action on a digital screen.

The phantom pixel is another thing some webmasters do to get better rankings.

Unfortunately it will backfire on you since the search engines do not want this to occur.

You see, the phantom pixel is when you might have a 1 pixel image or an image so small

it cannot be seen by the regular eye. They use the pixel to stuff it with keywords. The

search engine can view it in the code, which is how they know it is there and can give you

better rank for the keywords in theory. Of course since the search engines don’t like this

phantom pixel you are instead not getting anything for the extra keywords except sent to

the bottomless pit.

1.6.1 Early Technology

In the initial period of tracking only two radios were used to exchange the

information. One radio was attached to the vehicle while another at base station by which

drivers were enabled to talk to their masters. Fleet operator could identify the progress

through their routes.

The technology was not without its limits. It was restricted by the distance which

became a hurdle in accuracy and better connectivity between driver and fleet operators.

Base station was dependent on the driver for the information and a huge size fleet could

not have been managed depending on man-power only.

The scene of vehicle tracking underwent a change with the arrival of GPStechnology. This reduced the dependence on man-power. Most of the work of tracking

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became electronic. Computers proved a great help in managing a large fleet of vehicle.

This also made the information authentic. As this technology was available at affordable

cost all whether small or big fleet could take benefit of this technology

Because of the cheap accessibility of the device computer tracking facilities has

come to stay and associated with enhanced management. Today each vehicle carries

tracking unit which is monitored from the base station. Base station receives the data

from the unit.

All these facilities require a heavy investment of capital for the installation of the

infrastructure of tracking system for monitoring and dispatching

1.6.2 New development in technology

New system costs less with increased efficiency. Presently it is small tracking unit

in the vehicle with web-based interface, connected through a mobile phone. This device

avoids unnecessary investment in infrastructure with the facility of monitoring from

anywhere for the fleet managers. This provides more efficient route plan to fleet operators

of all sizes and compositions saving money and time.

Vehicle tracking system heralded a new era of convenience and affordability in fleet

management. Thus due to its easy availability it is going to stay for long.

1.7 Vehicle Tracking System Features

Monitoring and managing the mobile assets are very important for any company

dealing with the services, delivery or transport vehicles. Information technologies help in

supporting these functionalities from remote locations and update the managers with the

latest information of their mobile assets. Tracking the mobile assets locations data and

analyzing the information is necessary for optimal utilization of the assets.

Vehicle Tracking System is a software & hardware system enabling the vehicleowner to track the position of their vehicle. A vehicle tracking system uses either GPS or

radio technology to automatically track and record a fleet's field activities. Activity is

recorded by modules attached to each vehicle. And then the data is transmitted to a

central, internet-connected computer where it is stored. Once the data is transmitted to the

computer, it can be analyzed and reports can be downloaded in real-time to your

computer using either web browser based tools or customized software.

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1.7.1 Vehicle Tracking Benefits

An enterprise-level vehicle tracking system should offer customizable reporting

tools, for example to provide a summary of the any day activities. It should have the

ability to produce and print detailed maps and reports displaying actual stops, customerlocations, mileage traveled, and elapsed time at each location, and real-time access to

vehicle tracking data and reports. Vehicle tracking system can be active, passive or both

depending upon the application. Here are steps involved in the vehicle tracking:

i. Data capture: Data capturing is the first step in tacking your vehicle. Data in a

vehicle tracking system is captured through a unit called automated vehicle unit.

The automated vehicle unit uses the Global Positioning System (GPS) to

determine the location of the vehicle. This unit is installed in the vehicle and

contains interfaces to various data sources. This paper considers the location data

capture along with data from various sensors like fuel, vehicle diagnostic sensors

etc.

ii. Data storage: Captured data is stored in the memory of the automated vehicle

unit.

iii. Data transfer: Stored data are transferred to the computer server using the mobile

network or by connecting the vehicle mount unit to the computer.

iv. Data analysis: Data analysis is done through software application. A GIS

mapping component is also an integral part of the vehicle tracking system and it is

used to display the correct location of the vehicle on the map.

1.8 Vehicle Tracing in India

Vehicle tracking system in India is mainly used in transport industry that keeps a

real-time track of all vehicles in the fleet. The tracking system consists of GPS device that

brings together GPS and GSM technology using tracking software. The attached GPS unit

in the vehicle sends periodic updates of its location to the route station through the server

of the cellular network that can be displayed on a digital map. The location details are

later transferred to users via SMS, e-mail or other form of data transfers.

There are various GPS software and hardware developing companies in India

working for tracking solutions. However, its application is not that much of popular as in

other countries like USA, which regulates the whole GPS network. In India it is mostly

used in Indian transport and logistics industry and not much personal vehicle tracking.

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But with better awareness and promotion the market will increase. Let’s have a look at its

current application in India using vehicle tracking though in less volume.

a)

Freight forwarding

Logistic service providers are now increasingly adopting vehicle-tracking systemfor better fleet management and timely service. The system can continuously monitor

shipment location and so can direct the drivers directly in case of any change of plan.

Fleet managers can keep an eye on all activities of workers, vehicle over speed, route

deviation etc. The driver in turn can access emergency service in case of sickness,

accident or vehicle breakdown. All in turn supports money and time management,

resulting better customer service.

b)

Call centersIn commercial vehicle segments the taxi operators of various call centers are now

using vehicle tracking system for better information access. However, its application is in

its infant stage in India and if adequate steps are taken in bringing the cost of hardware

and software low then it can be used for tracking personal vehicle, farming (tractor),

tourist buses, security and emergency vehicle etc. Again Government needs to cut down

the restriction imposed upon the availability of digital maps for commercial use and this

will encourage software industry in developing cost-effective tracking solutions. Though,

sales of both commercial and passenger vehicles are growing but price of tracking service

is very high and this is the key issue in Indian market. Hence, it’s important for market

participants to reduce prices of GPS chips and other products in order to attract more and

more users.

As far as Indian vehicle tracking and navigation market is concerned the recent

association of India with Russian Global Navigation Satellite System (GLONASS) will

act as a catalyst in the improvement of vehicle tracking system. This will give an

advantage in managing traffic, roadways and ports and also as an important tool for

police and security agency to track stolen vehicles. Hence, in near future there is large

prospect for the utility of vehicle tracking system in India, which can revolutionize the

way we are communicating.

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Chapter 2

Block Diagram of VTS

2.1 Block Diagram of Vehicle Tracing Using GSM and GPS Modem

Figure 2.1 Block diagram

2.2 Hardware Components

AT89S52

GPS MODULE

GSM MODULE

RS232

MAX 232

RELAY

LCD

In this project AT89S52 microcontroller is used for interfacing to various hardware

peripherals. The current design is an embedded application, which will continuously

monitor a moving Vehicle and report the status of the Vehicle on demand. For doing so

an AT89S52 microcontroller is interfaced serially to a GSM Modem and GPS Receiver.

A GSM modem is used to send the position (Latitude and Longitude) of the vehicle froma remote place. The GPS modem will continuously give the data i.e. the latitude and

longitude indicating the position of the vehicle. The GPS modem gives many parameters

as the output, but only the NMEA data coming out is read and displayed on to the LCD.

The same data is sent to the mobile at the other end from where the position of the vehicle

is demanded. An EEPROM is used to store the mobile number.

The hardware interfaces to microcontroller are LCD display, GSM modem and GPS

Receiver. The design uses RS-232 protocol for serial communication between the

modems and the microcontroller. A serial driver IC is used for converting TTL voltage

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levels to RS-232 voltage levels. When the request by user is sent to the number at the

modem, the system automatically sends a return reply to that mobile indicating the

position of the vehicle in terms of latitude and longitude.

As the Micro Controller, GPS and GSM take a sight of in depth knowledge, they are

explained in the next chapters.

2.2.1 GPS

GPS, in full Global Positioning System, space-based radio-navigation system that

broadcasts highly accurate navigation pulses to users on or near the Earth. In the United

States’ Navstar GPS, 24 main satellites in 6 orbits circle the Earth every 12 hours. In

addition, Russia maintains a constellation called GLONASS (Global Navigation Satellite

System).

2.2.1.1 Working of GPS

GPS receiver works on 9600 baud rate is used to receive the data from space

Segment (from Satellites), the GPS values of different Satellites are sent to

microcontroller AT89S52, where these are processed and forwarded to GSM. At the time

of processing GPS receives only $GPRMC values only. From these values

microcontroller takes only latitude and longitude values excluding time, altitude, name of

the satellite, authentication etc. E.g. LAT: 1728:2470 LOG: 7843.3089 GSM modem with

a baud rate 57600.

A GPS receiver operated by a user on Earth measures the time it takes radio signals

to travel from four or more satellites to its location, calculates the distance to each

satellite, and from this calculation determines the user’s longitude, latitude, and altitude.

The U.S. Department of Defense originally developed the Navstar constellation for

military use, but a less precise form of the service is available free of charge to civilianusers around the globe. The basic civilian service will locate a receiver within 10 meters

(33 feet) of its true location, though various augmentation techniques can be used to

pinpoint the location within less than 1 cm (0.4 inch). With such accuracy and the

ubiquity of the service, GPS has evolved far beyond its original military purpose and has

created a revolution in personal and commercial navigation. Battlefield missiles and

artillery projectiles use GPS signals to determine their positions and velocities, but so do

the U.S. space shuttle and the International Space Station as well as commercial jetliners

and private airplanes. Ambulance fleets, family automobiles, and railroad locomotives

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benefit from GPS positioning, which also serves farm tractors, ocean liners, hikers, and

even golfers. Many GPS receivers are no larger than a pocket calculator and are powered

by disposable batteries, while GPS computer chips the size of a baby’s fingernail have

been installed in wristwatches, cellular telephones, and personal digital assistants.

2.2.1.2 Triangulation

The principle behind the unprecedented navigational capabilities of GPS is

triangulation. To triangulate, a GPS receiver precisely measures the time it takes for a

satellite signal to make its brief journey to Earth—less than a tenth of a second. Then it

multiplies that time by the speed of a radio wave—300,000 km (186,000 miles) per

second—to obtain the corresponding distance between it and the satellite. This puts the

receiver somewhere on the surface of an imaginary sphere with a radius equal to itsdistance from the satellite. When signals from three other satellites are similarly

processed, the receiver’s built-in computer calculates the point at which all four spheres

intersect, effectively determining the user’s current longitude, latitude, and altitude. (In

theory, three satellites would normally provide an unambiguous three-dimensional fix,

but in practice at least four are used to offset inaccuracy in the receiver’s clock.) In

addition, the receiver calculates current velocity (speed and direction) by measuring the

instantaneous Doppler effect shifts created by the combined motion of the same four

satellites.

2.2.1.3 Augmentation

Although the travel time of a satellite signal to Earth is only a fraction of a second,

much can happen to it in that interval. For example, electrically charged particles in the

ionosphere and density variations in the troposphere may act to slow and distort satellite

signals. These influences can translate into positional errors for GPS users—a problem

that can be compounded by timing errors in GPS receiver clocks. Further errors may be

introduced by relativistic time dilations, a phenomenon in which a satellite’s clock and a

receiver’s clock, located in different gravitational fields and traveling at different

velocities, tick at different rates. Finally, the single greatest source of error to users of the

Navstar system is the lower accuracy of the civilian C/A-code pulse. However, various

augmentation methods exist for improving the accuracy of both the military and the

civilian systems.

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When positional information is required with pinpoint precision, users can take

advantage of differential GPS techniques. Differential navigation employs a stationary

“base station” that sits at a known position on the ground and continuously monitors the

signals being broadcast by GPS satellites in its view. It then computes and broadcasts

real-time navigation corrections to nearby roving receivers. Each roving receiver, in

effect, subtracts its position solution from the base station’s solution, thus eliminating any

statistical errors common to the two. The U.S. Coast Guard maintains a network of such

base stations and transmits corrections over radio beacons covering most of the United

States. Other differential corrections are encoded within the normal broadcasts of

commercial radio stations. Farmers receiving these broadcasts have been able to direct

their field equipment with great accuracy, making precision farming a common term in

agriculture.

Another GPS augmentation technique uses the carrier waves that convey the

satellites’ navigation pulses to Earth. Because the length of the carrier wave is more than

1,000 times shorter than the basic navigation pulses, this “carrier-aided” approach, under

the right circumstances, can reduce navigation errors to less than 1 cm (0.4 inch). The

dramatically improved accuracy stems primarily from the shorter length and much greater

numbers of carrier waves impinging on the receiver’s antenna each second.

Yet another augmentation technique is known as geosynchronous overlays.

Geosynchronous overlays employ GPS payloads “piggybacked” aboard commercial

communication satellites that are placed in geostationary orbit some 35,000 km (22,000

miles) above the Earth. These relatively small payloads broadcast civilian C/A-code pulse

trains to ground-based users. The U.S. government is enlarging the Navstar constellation

with geosynchronous overlays to achieve improved coverage, accuracy, and survivability.

Both the European Union and Japan are installing their own geosynchronous overlays.

2.2.2 GSM

GSM (or Global System for Mobile Communications) was developed in 1990. The

first GSM operator has subscribers in 1991, the beginning of 1994 the network based on

the standard, already had 1.3 million subscribers, and the end of 1995 their number had

increased to 10 million!

There were first generation mobile phones in the 70's, there are 2nd generation

mobile phones in the 80's and 90's, and now there are 3rd gen phones which are about to

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enter the Indian market. GSM is called a 2nd generation, or 2G communications

technology.

In this project it acts as a SMS Receiver and SMS sender. The GSM technical

specifications define the different entities that form the GSM network by defining their

functions and interface requirements.

2.2.3 RS232 Interface

In telecommunications, RS-232 is the traditional name for a series of standards

for serial binary single-ended data and control signals connecting between a DTE (Data

Terminal Equipment) and a DCE (Data Circuit-terminating Equipment). It is commonly

used in computer serial ports. The standard defines the electrical characteristics and

timing of signals, the meaning of signals, and the physical size and pin out of connectors.

The current version of the standard is TIA-232-F Interface between Data Terminal

Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data

Interchange, issued in 1997.

An RS-232 port was once a standard feature of a personal computer for connections

to modems, printers, mice, data storage, un-interruptible power supplies, and other

peripheral devices. However, the limited transmission speed, relatively large voltage

swing, and large standard connectors motivated development of the universal serial

bus which has displaced RS-232 from most of its peripheral interface roles. Many modern

personal computers have no RS-232 ports and must use an external converter to connect

to older peripherals. Some RS-232 devices are still found especially in industrial

machines or scientific instruments.

Figure 2.2: 25 pin connector as described in the RS-232 standard

2.2.3.1 The scope of the standard

The Electronic Industries Association (EIA) standard RS-232-C[1] as of 1969

defines:

Electrical signal characteristics such as voltage levels, signaling rate, timing

and slew-rate of signals, voltage withstand level, short-circuit behavior, and

maximum load capacitance.

Interface mechanical characteristics, pluggable connectors and pin identification.

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Functions of each circuit in the interface connector.

Standard subsets of interface circuits for selected telecom applications.

The standard does not define such elements as the character encoding or the framing

of characters, or error detection protocols. The standard does not define bit rates for

transmission, except that it says it is intended for bit rates lower than 20,000 bits per

second. Many modern devices support speeds of 115,200 bit/s and above. RS 232 makes

no provision for power to peripheral devices.

Details of character format and transmission bit rate are controlled by the serial

port hardware, often a single integrated circuit called a UART that converts data from

parallel to asynchronous start-stop serial form. Details of voltage levels, slew rate, and

short-circuit behavior are typically controlled by a line driver that converts from the

UART's logic levels to RS-232 compatible signal levels, and a receiver that converts from

RS-232 compatible signal levels to the UART's logic levels.

2.2.3.2 History of RS 232

RS-232 was first introduced in 1962. The original DTEs were

electromechanical teletypewriters, and the original DCEs were (usually) modems.

When electronic terminals (smart and dumb) began to be used, they were often designed

to be interchangeable with teletypewriters, and so supported RS-232. The C revision of

the standard was issued in 1969 in part to accommodate the electrical characteristics of

these devices.

Since application to devices such as computers, printers, test instruments, and so on

was not considered by the standard, designers implementing an RS-232 compatible

interface on their equipment often interpreted the requirements idiosyncratically.

Common problems were non-standard pin assignment of circuits on connectors, and

incorrect or missing control signals. The lack of adherence to the standards produced a

thriving industry of breakout boxes, patch boxes, test equipment, books, and other aids

for the connection of disparate equipment. A common deviation from the standard was to

drive the signals at a reduced voltage. Some manufacturers therefore built transmitters

that supplied +5 V and -5 V and labeled them as "RS-232 compatible".

Later personal computers (and other devices) started to make use of the standard so

that they could connect to existing equipment. For many years, an RS-232-compatible port was a standard feature for serial communications, such as modem connections, on

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many computers. It remained in widespread use into the late 1990s. In personal computer

peripherals, it has largely been supplanted by other interface standards, such as USB. RS-

232 is still used to connect older designs of peripherals, industrial equipment (such

as PLCs), console ports, and special purpose equipment, such as a cash drawer for a cash

register.

The standard has been renamed several times during its history as the sponsoring

organization changed its name, and has been variously known as EIA RS-232, EIA 232,

and most recently as TIA 232. The standard continued to be revised and updated by

the Electronic Industries Alliance and since 1988 by the Telecommunications Industry

Association (TIA).[3] Revision C was issued in a document dated August 1969. Revision

D was issued in 1986. The current revision is TIA-232-F Interface between Data

Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary

Data Interchange, issued in 1997. Changes since Revision C have been in timing and

details intended to improve harmonization with the CCITT standard V.24, but equipment

built to the current standard will interoperate with older versions.

Related ITU-T standards include V.24 (circuit identification) and V.28 (signal

voltage and timing characteristics).

2.2.3.3 Limitation of Standard

Because the application of RS-232 has extended far beyond the original purpose of

interconnecting a terminal with a modem, successor standards have been developed to

address the limitations.

Issues with the RS-232 standard include:

The large voltage swings and requirement for positive and negative supplies

increases power consumption of the interface and complicates power supply design.

The voltage swing requirement also limits the upper speed of a compatible interface.

Single-ended signaling referred to a common signal ground limits the noise

immunity and transmission distance.

Multi-drop connection among more than two devices is not defined. While multi-

drop "work-arounds" have been devised, they have limitations in speed and

compatibility.

Asymmetrical definitions of the two ends of the link make the assignment of the

role of a newly developed device problematic; the designer must decide on either aDTE-like or DCE-like interface and which connector pin assignments to use.

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The handshaking and control lines of the interface are intended for the setup and

takedown of a dial-up communication circuit; in particular, the use of handshake

lines for flow control is not reliably implemented in many devices.

No method is specified for sending power to a device. While a small amount of

current can be extracted from the DTR and RTS lines, this is only suitable for low

power devices such as mice.

The 25-way connector recommended in the standard is large compared to current

practice.

2.2.3.4 Standard details

In RS-232, user data is sent as a time-series of bits. Both synchronous and

asynchronous transmissions are supported by the standard. In addition to the data circuits,

the standard defines a number of control circuits used to manage the connection between

the DTE and DCE. Each data or control circuit only operates in one direction, that is,

signaling from a DTE to the attached DCE or the reverse. Since transmit data and receive

data are separate circuits, the interface can operate in a full duplex manner, supporting

concurrent data flow in both directions. The standard does not define character framing

within the data stream, or character encoding.

Voltage levels

Figure 2.3 Diagrammatic oscilloscope trace of voltage levels for an uppercase ASCII "K" character (0x4b)

with 1 start bit, 8 data bits, 1 stop bit.

This is typical for start-stop communications, but the standard does not dictate a character

format or bit order.

The RS-232 standard defines the voltage levels that correspond to logical one and logical

zero levels for the data transmission and the control signal lines. Valid signals are plus or

minus 3 to 15 volts; the ±3 V range near zero volts is not a valid RS-232 level.

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Figure 2.4 Upper Picture: RS232 signaling as seen when probed by an actual oscilloscope (Tektronix

MSO4104B) for an uppercase ASCII "K" character (0x4b) with 1 start bit (always), 8 data bits, 1 stop bit

and no parity bits (8N1)

The standard specifies a maximum open-circuit voltage of 25 volts: signal levels of

±5 V, ±10 V, ±12 V, and ±15 V are all commonly seen depending on the power

supplies available within a device. RS-232 drivers and receivers must be able to withstand

indefinite short circuit to ground or to any voltage level up to ±25 volts. The slew rate, or

how fast the signal changes between levels, is also controlled.

For data transmission lines (TxD, RxD and their secondary channel equivalents)

logic one is defined as a negative voltage, the signal condition is called marking, and has

the functional significance. Logic zero is positive and the signal condition is termed

spacing. Control signals are logically inverted with respect to what one sees on the data

transmission lines. When one of these signals is active, the voltage on the line will be

between +3 to +15 volts. The inactive state for these signals is the opposite voltage

condition, between −3 and −15 volts. Examples of control lines include request to send

(RTS), clear to send (CTS), data terminal ready (DTR), and data set ready (DSR).

Because the voltage levels are higher than logic levels typically used by integrated

circuits, special intervening driver circuits are required to translate logic levels. These

also protect the device's internal circuitry from short circuits or transients that may appear

on the RS-232 interface, and provide sufficient current to comply with the slew rate

requirements for data transmission.

Because both ends of the RS-232 circuit depend on the ground pin being zero volts,

problems will occur when connecting machinery and computers where the voltage

between the ground pin on one end and the ground pin on the other is not zero. This may

also cause a hazardous ground loop. Use of a common ground limits RS-232 toapplications with relatively short cables. If the two devices are far enough apart or on

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separate power systems, the local ground connections at either end of the cable will have

differing voltages; this difference will reduce the noise margin of the signals. Balanced,

differential, serial connections such as USB, RS-422 and RS-485 can tolerate larger

ground voltage differences because of the differential signaling.

Unused interface signals terminated to ground will have an undefined logic state.

Where it is necessary to permanently set a control signal to a defined state, it must be

connected to a voltage source that asserts the logic 1 or logic 0 level. Some devices

provide test voltages on their interface connectors for this purpose.

2.2.3.5 Connectors

RS-232 devices may be classified as Data Terminal Equipment (DTE) or Data

Communication Equipment (DCE); this defines at each device which wires will be

sending and receiving each signal. The standard recommended but did not make

mandatory the D-subminiature 25 pin connector. In general and according to the standard,

terminals and computers have male connectors with DTE pin functions, and modems

have female connectors with DCE pin functions. Other devices may have any

combination of connector gender and pin definitions. Many terminals were manufactured

with female terminals but were sold with a cable with male connectors at each end; the

terminal with its cable satisfied the recommendations in the standard.

Presence of a 25 pin D-sub connector does not necessarily indicate an RS-232-C

compliant interface. For example, on the original IBM PC, a male D-sub was an RS-232-

C DTE port (with a non-standard current loop interface on reserved pins), but the female

D-sub connector was used for a parallel Centronics printer port. Some personal

computers put non-standard voltages or signals on some pins of their serial ports.The

standard specifies 20 different signal connections. Since most devices use only a few

signals, smaller connectors can often be used.

The following table lists commonly used RS-232 signals and pin assignments.

The signals are named from the standpoint of the DTE. The ground signal is a

common return for the other connections. The DB-25 connector includes a second

"protective ground" on pin 1.

Data can be sent over a secondary channel (when implemented by the DTE and

DCE devices), which is equivalent to the primary channel. Pin assignments are described

in shown in Table 2.2:

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Table 2.1. Commonly used RS-232 signals and pin assignments

Signal Origin

DB-25 pin

Name Typical purpose Abbreviation DTE DCE

Data

Terminal Ready

Indicates presence of

DTE to DCE.DTR ● 20

Data

Carrier Detect

DCE is connected to the

telephone line.DCD ● 8

Data Set Ready

DCE is ready to receive

commands or data. DSR ● 6

Ring Indicator

DCE has detected an

incoming ring signal on

the telephone line.

RI ● 22

Request To

Send

DTE requests the DCE

prepare to receive data.RTS ● 4

Clear To SendIndicates DCE is ready to

accept data.CTS ● 5

Transmitted

Data

Carries data from DTE to

DCE.TxD ● 2

Received DataCarries data from DCE to

DTE.RxD ● 3

Common

GroundGND common 7

Protective

GroundPG common 1

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Table 2.2 Pin assignments

Signal Pin

Common Ground 7 (same as primary)

Secondary Transmitted Data (STD) 14

Secondary Received Data (SRD) 16

Secondary Request To Send (SRTS) 19

Secondary Clear To Send (SCTS) 13

Secondary Carrier Detect (SDCD) 12

Ring Indicator' (RI), is a signal sent from the modem to the terminal device. It

indicates to the terminal device that the phone line is ringing. In many computer serial

ports, a hardware interrupt is generated when the RI signal changes state. Having support

for this hardware interrupt means that a program or operating system can be informed of a

change in state of the RI pin, without requiring the software to constantly "poll" the state

of the pin. RI is a one-way signal from the modem to the terminal (or more generally, the

DCE to the DTE) that does not correspond to another signal that carries similar

information the opposite way.

On an external modem the status of the Ring Indicator pin is often coupled to the

"AA" (auto answer) light, which flashes if the RI signal has detected a ring. The asserted

RI signal follows the ringing pattern closely, which can permit software to

detect distinctive ring patterns.

The Ring Indicator signal is used by some older uninterruptible power

supplies (UPS's) to signal a power failure state to the computer.

Certain personal computers can be configured for wake-on-ring, allowing a

computer that is suspended to answer a phone call.

2.2.3.6 Cables

The standard does not define a maximum cable length but instead defines the

maximum capacitance that a compliant drive circuit must tolerate. A widely used rule of

thumb indicates that cables more than 50 feet (15 m) long will have too much

capacitance, unless special cables are used. By using low-capacitance cables, full speed

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communication can be maintained over larger distances up to about 1,000 feet

(300 m).[8] For longer distances, other signal standards are better suited to maintain high

speed.

Since the standard definitions are not always correctly applied, it is often necessary

to consult documentation, test connections with a breakout box, or use trial and error to

find a cable that works when interconnecting two devices. Connecting a fully standard-

compliant DCE device and DTE device would use a cable that connects identical pin

numbers in each connector (a so-called "straight cable"). "Gender changers" are available

to solve gender mismatches between cables and connectors. Connecting devices with

different types of connectors requires a cable that connects the corresponding pins

according to the table above. Cables with 9 pins on one end and 25 on the other are

common. Manufacturers of equipment with 8P8C connectors usually provide a cable with

either a DB-25 or DE-9 connector (or sometimes interchangeable connectors so they can

work with multiple devices). Poor-quality cables can cause false signals

by crosstalk between data and control lines (such as Ring Indicator). If a given cable will

not allow a data connection, especially if a Gender changer is in use, a Null modem may

be necessary.

2.2.3.7 Conventions

For functional communication through a serial port interface, conventions of bit

rate, character framing, communications protocol, character encoding, data compression,

and error detection, not defined in RS 232, must be agreed to by both sending and

receiving equipment. For example, consider the serial ports of the original IBM PC. This

implementation used an 8250 UART using asynchronous start-stop character formatting

with 7 or 8 data bits per frame, usually ASCII character coding, and data rates

programmable between 75 bits per second and 115,200 bits per second. Data rates above

20,000 bits per second are out of the scope of the standard, although higher data rates are

sometimes used by commercially manufactured equipment. Since most RS-232 devices

do not have automatic baud rate detection, users must manually set the baud rate (and all

other parameters) at both ends of the RS-232 connection.

In the particular case of the IBM PC, as with most UART chips including the 8250

UART used by the IBM PC, baud rates were programmable with arbitrary values. Thisallowed a PC to be connected to devices not using the rates typically used with modems.

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Not all baud rates can be programmed, due to the clock frequency of the 8250 UART in

the PC, and the granularity of the baud rate setting. This includes the baud rate of MIDI,

31,250 bits per second, which is generally not achievable by a standard IBM PC serial

port. MIDI-to-RS-232 interfaces designed for the IBM PC include baud rate translation

hardware to adjust the baud rate of the MIDI data to something that the IBM PC can

support, for example 19,200 or 38,400 bits per second.

2.2.3.8 RTS/CTS handshaking

In older versions of the specification, RS-232's use of the RTS and CTS lines is

asymmetric: The DTE asserts RTS to indicate a desire to transmit to the DCE, and the

DCE asserts CTS in response to grant permission. This allows for half-duplex modems

that disable their transmitters when not required, and must transmit a synchronization

preamble to the receiver when they are re-enabled. This scheme is also employed on

present-day RS-232 to RS-485 converters, where the RS-232's RTS signal is used to ask

the converter to take control of the RS-485 bus - a concept that does not otherwise exist in

RS-232. There is no way for the DTE to indicate that it is unable to accept data from the

DCE.

A non-standard symmetric alternative, commonly called "RTS/CTS handshaking,"

was developed by various equipment manufacturers. In this scheme, CTS is no longer a

response to RTS; instead, CTS indicates permission from the DCE for the DTE to send

data to the DCE, and RTS indicates permission from the DTE for the DCE to send data to

the DTE. RTS and CTS are controlled by the DTE and DCE respectively, each

independent of the other. This was eventually codified in version RS-232-E (actually

TIA-232-E by that time) by defining a new signal, "RTR (Ready to Receive)," which is

CCITT V.24 circuit 133. TIA-232-E and the corresponding international standards were

updated to show that circuit 133, when implemented, shares the same pin as RTS

(Request to Send), and that when 133 is in use, RTS is assumed by the DCE to be ON at

all times.

Thus, with this alternative usage, one can think of RTS asserted (positive voltage,

logic 0) meaning that the DTE is indicating it is "ready to receive" from the DCE, rather

than requesting permission from the DCE to send characters to the DCE.

Note that equipment using this protocol must be prepared to buffer some extra data,

since a transmission may have begun just before the control line state change.

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RTS/CTS handshaking is an example of hardware flow control. However,

"hardware flow control" in the description of the options available on an RS-232-

equipped device does not always mean RTS/CTS handshaking.

2.2.3.9 3-wire and 5-wire RS-232

Minimal “3-wire” RS-232 connections’ consisting only of transmit data, receive

data, and ground, is commonly used when the full facilities of RS-232 are not required.

Even a two-wire connection (data and ground) can be used if the data flow is one way

(for example, a digital postal scale that periodically sends a weight reading, or a GPS

receiver that periodically sends position, if no configuration via RS-232 is necessary).

When only hardware flow control is required in addition to two-way data, the RTS and

CTS lines are added in a 5-wire version.

2.2.3.10 Seldom used features

The EIA-232 standard specifies connections for several features that are not used in

most implementations. Their use requires the 25-pin connectors and cables, and of course

both the DTE and DCE must support them.

a) Signal rate selection

The DTE or DCE can specify use of a "high" or "low" signaling rate. The rates as

well as which device will select the rate must be configured in both the DTE and DCE.

The prearranged device selects the high rate by setting pin 23 to ON.

b) Loopback testing

Many DCE devices have a loopback capability used for testing. When enabled,

signals are echoed back to the sender rather than being sent on to the receiver. If

supported, the DTE can signal the local DCE (the one it is connected to) to enter

loopback mode by setting pin 18 to ON, or the remote DCE (the one the local DCE is

connected to) to enter loopback mode by setting pin 21 to ON. The latter tests the

communications link as well as both DCE's. When the DCE is in test mode it signals the

DTE by setting pin 25 to ON.

A commonly used version of loopback testing does not involve any special

capability of either end. A hardware loopback is simply a wire connecting complementary

pins together in the same connector

Loopback testing is often performed with a specialized DTE called a bit error rate

tester (or BERT).

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2.2.3.11 Timing Signals

Some synchronous devices provide a clock signal to synchronize data transmission,

especially at higher data rates. Two timing signals are provided by the DCE on pins 15

and 17. Pin 15 is the transmitter clock, or send timing (ST); the DTE puts the next bit onthe data line (pin 2) when this clock transitions from OFF to ON (so it is stable during the

ON to OFF transition when the DCE registers the bit). Pin 17 is the receiver clock, or

receive timing (RT); the DTE reads the next bit from the data line (pin 3) when this clock

transitions from ON to OFF.

Alternatively, the DTE can provide a clock signal, called transmitter timing (TT), on

pin 24 for transmitted data. Data is changed when the clock transitions from OFF to ON

and read during the ON to OFF transition. TT can be used to overcome the issue where

ST must traverse a cable of unknown length and delay, clock a bit out of the DTE after

another unknown delay, and return it to the DCE over the same unknown cable delay.

Since the relation between the transmitted bit and TT can be fixed in the DTE design, and

since both signals traverse the same cable length, using TT eliminates the issue. TT may

be generated by looping ST back with an appropriate phase change to align it with the

transmitted data. ST loop back to TT lets the DTE use the DCE as the frequency

reference, and correct the clock to data ti

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