Door Locking Security System Using Gsm Module

List of Contents
Abstract

3

1. Introduction

4

2. Objective of the project

5

2.1 Background of the Project

5

3. Overview of the technologies used

6

3.1. Embedded Systems

6

3.2 The Evolution of Mobile Telephone Systems

7

4. Hardware Implementation of the Project

9

4.1. Project Design

9

4.2. Block Diagram of the Project and its Description

10

4.3. Power Supply

11

4.4. Microcontrollers

12

4.5 GSM Technology

53

4.6 Serial Communication

60

4.7 L293D- Current Driver

84

4.8 Electric Motors

94

4.9 LIQUID CRYSTAL DISPLAY

96

1

5. Projects Schematic diagram
5.1 Working procedure
6. Firmware Implementation of the project design

96
97
98

6.1. Software Tools Required

98

6.2. Programming Microcontroller

98

6.3. Project Source code

104

7. Results and Discussion

114

8. APPLICATIONS & Advantages
9. FUTURE SCOPE
10. REFRENCES AND BIBLOGRAPHY

2

DOOR LOCKING SECURITY SYSTEM UING GSM
ABSTRACT
The main aim of this project is to provide security at homes, offices etc. The
system automatically locks the door as soon as it receives a predefined message from the user.
This project uses the wireless communication, GSM. To receive the messages from the
user mobile, we need a GSM modem. This modem will be interfaced to the microcontroller
through serial interface. A modem provides the communication interface. It transports device
protocols transparently over the network through a serial interface. A GSM modem is a wireless
modem that works with a GSM wireless network. A wireless modem behaves like a dial-up
modem. The main difference between them is that a dial-up modem sends and receives data
through a fixed telephone line while a wireless modem sends and receives data through radio
waves.
If the user is somewhere far from the main door and he wants to close the main door right from
the place he is standing, he has to send a predefined message to the modem. The controlling unit
will be fixed at the main door. The controlling unit contains the microcontroller and the GSM
modem interfaced to it. The microcontroller continuously checks whether it has received any
message from the modem.
When the user sends the predefined message to the modem, the modem receives the message and
intimates the same to the microcontroller. The microcontroller retrieves this message from the
modem by issuing certain AT and T commands to the modem. Thus, after receiving the message
from the modem, the microcontroller automatically closes the door by rotating the stepper motor
fixed to the door. This will be done perfectly without the involvement of any human.
This project uses regulated 5V, 500mA power supply. 7805 three terminal voltage
regulator is used for voltage regulation. Bridge type full wave rectifier is used to rectify the ac
out put of secondary of 230/12V step down transformer.

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1. Introduction
Security is prime concern in our day-to-day life. Everyone wants to be as much as secure as to be
possible. An access control systems forms a vital link in a security chain. The micro controller
based digital lock presented here is an access control system that allows only authorized persons
to access a restricted area. This system is best suitable for corporate offices, ATMs and home
security.
The system comprises a small electronic unit with a numeric keypad, which infixed outside the
entry door to control a solenoid-operated lock with the help of a stepper motor. When an
authorized person enters predetermined user ID and password
via the keypad, the stepper motor is operated for a limited time to unlatch the solenoid-operated
lock so the door can be open. At the end of preset delay, the stepper motor is operated in reverse
direction and the door gets locked again. When the code has been incorrectly entered three times
in a row, the code lock will switch to block mode. This function thwarts any attempt by „hackers‟
to quickly try a large number of codes in a sequence. If the user forgets his password, the code
lock can be accessed by a unique 10 digit administrator password. The secret code can be
changed any time after entering the current code (Master code).

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2. Objective of the project
The project intends to interface the microcontroller with the GSM modem and start/stop the
vehicle engine by sending the predefined messages from the mobile to the controlling unit. The
project uses the GSM technology and Embedded Systems to design this application. The main
objective of this project is to design a system that continuously checks the messages if any,
received from the user mobile and change the status of the engine as per the message received
from the mobile through the modem.
This project is a device that collects data from the mobile, codes the data into a format that
can be understood by the controlling section. This system controls the engine motor as per the
message received from the mobile.
The objective of the project is to develop a microcontroller based control system. It consists
of a GSM modem, microcontroller, the interfacing unit to allow the communication between the
microcontroller and mobile and the required circuitry.

1.1 Background of the Project
The software application and the hardware implementation help the microcontroller read
the messages sent by the user from a mobile phone or send messages to the mobile phone
through the modem and accordingly change the status of the engine motor required. The measure
of efficiency is based on how fast the microcontroller can detect the incoming message and act
accordingly. The system is totally designed using GSM and embedded systems technology.
The Controlling unit has an application program to allow the microcontroller read the
incoming data through the modem and control the engine motor as per the requirement. The
performance of the design is maintained by controlling unit.

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3. Overview of the technologies used
3.1. Embedded Systems:
An embedded system can be defined as a computing device that does a specific focused job.
Appliances such as the air-conditioner, VCD player, DVD player, printer, fax machine, mobile
phone etc. are examples of embedded systems. Each of these appliances will have a processor
and special hardware to meet the specific requirement of the application along with the
embedded software that is executed by the processor for meeting that specific requirement. The
embedded software is also called “firm ware”. The desktop/laptop computer is a general purpose
computer. You can use it for a variety of applications such as playing games, word processing,
accounting, software development and so on. In contrast, the software in the embedded systems
is always fixed listed below:
· Embedded systems do a very specific task, they cannot be programmed to do different things.
. Embedded systems have very limited resources, particularly the memory. Generally, they do
not have secondary storage devices such as the CDROM or the floppy disk. Embedded systems
have to work against some deadlines. A specific job has to be completed within a specific time.
In some embedded systems, called real-time systems, the deadlines are stringent. Missing a
deadline may cause a catastrophe-loss of life or damage to property. Embedded systems are
constrained for power. As many embedded systems operate through a battery, the power
consumption has to be very low.

Some embedded systems have to operate in extreme

environmental conditions such as very high temperatures and humidity.
Following are the advantages of Embedded Systems:
1. They are designed to do a specific task and have real time performance constraints which
must be met.
2. They allow the system hardware to be simplified so costs are reduced.
3. They are usually in the form of small computerized parts in larger devices which serve a
general purpose.
4. The program instructions for embedded systems run with limited computer hardware
resources, little memory and small or even non-existent keyboard or
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3.2 The Evolution of Mobile Telephone Systems
Cellular is one of the fastest growing and most demanding telecommunications applications.
Today, it represents a continuously increasing percentage of all new telephone subscriptions
around the world. Currently there are more than 45 million cellular subscribers worldwide, and
nearly 50 percent of those subscribers are located in the United States.
The concept of cellular service is the use of low power transmitters where frequencies can be
reused within a geographic area. The idea of cell based mobile radio service was formulated in
the United States at Bell Labs in the early 1970s. Cellular systems began in the United States
with the release of the advanced mobile phone service (AMPS) system in 1983. The AMPS
standard was adopted by Asia, Latin America and Oceanic countries, creating the largest
potential market in the world for cellular.
In the early 1980s, most mobile telephone systems were analog rather than digital, like today's
newer systems. One challenge facing analog systems was the inability to handle the growing
capacity needs in a cost efficient manner. As a result, digital technology was welcomed.
The advantages of digital systems over analog systems include ease of signaling, lower levels of
interference, integration of transmission and switching and increased ability to meet capacity
demands. The table below shows the worldwide development of mobile telephone systems.

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4. Hardware Implementation of the Project
This chapter briefly explains about the Hardware Implementation of the project. It discusses the
design and working of the design with the help of block diagram and circuit diagram and
explanation of circuit diagram in detail. It explains the features, timer programming, serial
communication, interrupts of AT89S52 microcontroller. It also explains the various modules
used in this project.

4.1 Project Design
The implementation of the project design can be divided in two parts.
 Hardware implementation
 Firmware implementation

Hardware implementation deals in drawing the schematic on the plane paper according to the
application, testing the schematic design over the breadboard using the various IC‟s to find if the
design meets the objective, carrying out the PCB layout of the schematic tested on breadboard,
finally preparing the board and testing the designed hardware.
The firmware part deals in programming the microcontroller so that it can control the operation
of the IC‟s used in the implementation. In the present work, we have used the Orcad design
software for PCB circuit design, the Keil µv3 software development tool to write and compile
the source code, which has been written in the C language. The Proload programmer has been
used to write this compile code into the microcontroller. The firmware implementation is
explained in the next chapter.
The project design and principle are explained in this chapter using the block diagram and circuit
diagram. The block diagram discusses about the required components of the design and working
condition is explained using circuit diagram and system wiring diagram.
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4.2 Block Diagram of the Project and its Description

Fig: Block Diagram of the de s ign for Engine M otor control us ing GSM

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4.3 Power Supply:
The input to the circuit is applied from the regulated power supply. The a.c. input i.e., 230V from
the mains supply is step down by the transformer to 12V and is fed to a rectifier. The output
obtained from the rectifier is a pulsating d.c voltage. So in order to get a pure d.c voltage, the
output voltage from the rectifier is fed to a filter to remove any a.c components present even after
rectification. Now, this voltage is given to a voltage regulator to obtain a pure constant dc
voltage.

Transformer:
Usually, DC voltages are required to operate various electronic equipment and these
voltages are 5V, 9V or 12V. But these voltages cannot be obtained directly. Thus the a.c input
available at the mains supply i.e., 230V is to be brought down to the required voltage level. This
is done by a transformer. Thus, a step down transformer is employed to decrease the voltage to a
required level.

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Rectifier:
The output from the transformer is fed to the rectifier. It converts A.C. into pulsating
D.C. The rectifier may be a half wave or a full wave rectifier. In this project, a bridge rectifier is
used because of its merits like good stability and full wave rectification.
Filter:
Capacitive filter is used in this project. It removes the ripples from the output of rectifier
and smoothens the D.C. Output

received from this filter is constant until the mains voltage and

load is maintained constant. However, if either of the two is varied, D.C. voltage received at this
point changes. Therefore a regulator is applied at the output stage.
Voltage regulator:
As the name itself implies, it regulates the input applied to it. A voltage regulator is an
electrical regulator designed to automatically maintain a constant voltage level. In this project,
power supply of 5V and 12V are required. In order to obtain these voltage levels, 7805 and 7812
voltage regulators are to be used. The first number 78 represents positive supply and the numbers
05, 12 represent the required output voltage levels.

4.4 Microcontrollers:
Microprocessors and

microcontrollers are widely used in embedded systems products.

Microcontroller is a programmable device. A microcontroller has a CPU in addition to a fixed
amount of RAM, ROM, I/O ports and a timer embedded all on a single chip. The fixed amount
of on-chip ROM, RAM and number of I/O ports in microcontrollers makes them ideal for many
applications in which cost and space are critical.
The Intel 8051 is Harvard architecture, single chip microcontroller (µC) which was developed by
Intel in 1980 for use in embedded systems. It was popular in the 1980s and early 1990s, but
today it has largely been superseded by a vast range of enhanced devices with 8051-compatible
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processor cores that are manufactured by more than 20 independent manufacturers including
Atmel, Infineon Technologies and Maxim Integrated Products.
8051 is an 8-bit processor, meaning that the CPU can work on only 8 bits of data at a time. Data
larger than 8 bits has to be broken into 8-bit pieces to be processed by the CPU. 8051 is available
in different memory types such as UV-EPROM, Flash and NV-RAM.

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Features of AT89S52:


8K Bytes of Re-programmable Flash Memory.



RAM is 256 bytes.



4.0V to 5.5V Operating Range.



Fully Static Operation: 0 Hz to 33 MHz‟s



Three-level Program Memory Lock.



256 x 8-bit Internal RAM.



32 Programmable I/O Lines.



Three 16-bit Timer/Counters.



Eight Interrupt Sources.



Full Duplex UART Serial Channel.



Low-power Idle and Power-down Modes.



Interrupt recovery from power down mode.



Watchdog timer.



Dual data pointer.



Power-off flag.



Fast programming time.



Flexible ISP programming (byte and page mode).

Description:
The AT89s52 is a low-voltage, high-performance CMOS 8-bit microcomputer with 8K bytes of
Flash programmable memory.
nonvolatile

The device is manufactured

memory technology and

using Atmel‟s high density

is compatible with the industry-standard

MCS-51

instruction set. The on chip flash allows the program memory to be reprogrammed in system or
by a conventional non volatile memory programmer. By combining a versatile 8-bit CPU with
Flash on a monolithic chip, the Atmel AT89s52 is a powerful microcomputer, which provides a
highly flexible and cost-effective solution to many embedded control applications.

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In addition, the AT89s52 is designed with static logic for operation down to zero frequency and
supports two software selectable power saving modes. The Idle Mode stops the CPU while
allowing the RAM, timer/counters, serial port and interrupt system to continue functioning. The
power-down mode saves the RAM contents but freezes the oscillator disabling all other chip
functions until the next hardware reset.

Fig: Pin diagram

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Fig: Block diagram

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Pin description:
Vcc

Pin 40 provides supply voltage to the chip. The voltage source is +5V.

GND Pin 20 is the ground.
Port 0
Port 0 is an 8-bit open drain bidirectional I/O port. As an output port, each pin can sink eight
TTL inputs. When 1s are written to port 0 pins, the pins can be used as high impedance inputs.
Port 0 can also be configured to be the multiplexed low-order address/data bus during accesses to
external program and data memory. In this mode, P0 has internal pull-ups.
Port 0 also receives the code bytes during Flash programming and outputs the code bytes during
Program verification. External pull-ups are required during program verification.
Port 1
Port 1 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 1 output buffers can
sink/source four TTL inputs. When 1s are written to Port 1 pins, they are pulled high by the
internal pull-ups and can be used as inputs. As inputs, Port 1 pins that are externally being pulled
low will source current (IIL) because of the internal pull-ups. In addition, P1.0 and P1.1 can be
configured to be the timer/counter 2 external count input (P1.0/T2) and the timer/counter 2
trigger input (P1.1/T2EX), respectively, as shown in the following table.
Port 1 also receives the low-order address bytes during Flash programming and verification.

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Port 2
Port 2 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 2 output buffers can
sink/source four TTL inputs. When 1s are written to Port 2 pins, they are pulled high by the
internal pull-ups and can be used as inputs. As inputs, Port 2 pins that are externally being pulled
low will source current (IIL) because of the internal pull-ups.
Port 2 emits the high-order address byte during fetches from external program memory and
during accesses to external data memory that uses 16-bit addresses (MOVX @ DPTR). In this
application, Port 2 uses strong internal pull-ups when emitting 1s. During accesses to external
data memory that uses 8-bit addresses (MOVX @ RI), Port 2 emits the contents of the P2
Special Function Register. The port also receives the high-order address bits and some control
signals during Flash programming and verification.
Port 3
Port 3 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 3 output buffers can
sink/source four TTL inputs. When 1s are written to Port 3 pins, they are pulled high by the
internal pull-ups and can be used as inputs. As inputs, Port 3 pins that are externally being pulled
low will source current (IIL) because of the pull-ups. Port 3 receives some control signals for
Flash programming and verification.
Port 3 also serves the functions of various special features of the AT89S52, as shown in the
following table.

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RST
Reset input A high on this pin for two machine cycles while the oscillator is running resets the
device. This pin drives high for 98 oscillator periods after the Watchdog times out. The DISRTO
bit in SFR AUXR (address 8EH) can be used to disable this feature. In the default state of bit
DISRTO, the RESET HIGH out feature is enabled.
ALE/PROG
Address Latch Enable (ALE) is an output pulse for latching the low byte of the address during
accesses to external memory. This pin is also the program pulse input (PROG) during Flash
programming.
In normal operation, ALE is emitted at a constant rate of 1/6 the oscillator frequency and may be
used for external timing or clocking purposes. Note, however, that one ALE pulse is skipped
during each access to external data memory.
If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the bit set,
ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is weakly pulled
high. Setting the ALE-disable bit has no effect if the microcontroller is in external execution
mode.

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PSEN
Program Store Enable (PSEN) is the read strobe to external program memory. When the
AT89S52 is executing code from external program memory, PSEN is activated twice each
machine cycle, except that two PSEN activations are skipped during each access to external data
memory.
EA/VPP
External Access Enable EA must be strapped to GND in order to enable the device to fetch
code from external program memory locations starting at 0000H up to FFFFH. Note, however,
that if lock bit 1 is programmed, EA will be internally latched on reset.
EA should be strapped to VCC for internal program executions. This pin also receives the 12volt programming enable voltage (VPP) during Flash programming.
XTAL1
Input to the inverting oscillator amplifier and input to the internal clock operating circuit.
XTAL2
Output from the inverting oscillator amplifier.

Oscillator Connections

C1, C2 = 30 pF ± 10 pF for Crystals
= 40 pF ± 10 pF for Ceramic Resonators

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External Clock Drive Configuration

XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier that can be
configured for use as an on-chip oscillator. Either a quartz crystal or ceramic resonator may be
used. To drive the device from an external clock source, XTAL2 should be left unconnected
while XTAL1 is driven. There are no requirements on the duty cycle of the external clock signal,
since the input to the internal clocking circuitry is through a divide-by-two flip-flop, but
minimum and maximum voltage high and low time specifications must be observed.

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Special Function Registers
A map of the on-chip memory area called the Special Function Register (SFR) space is shown in
the following table.
It should be noted that not all of the addresses are occupied and unoccupied addresses may not
be implemented on the chip. Read accesses to these addresses will in general return random data,
and write accesses will have an indeterminate effect.
User software should not write 1s to these unlisted locations, since they may be used in future
products to invoke new features. In that case, the reset or inactive values of the new bits will
always be 0.
Timer 2 Registers:
Control and status bits are contained in registers T2CON and T2MOD for Timer 2. The register
pair (RCAP2H, RCAP2L) is the Capture/Reload register for Timer 2 in 16-bit capture mode or
16-bit auto-reload mode.
Interrupt Registers:
The individual interrupt enable bits are in the IE register. Two priorities can be set for each of the
six interrupt sources in the IP register.

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22

Dual Data Pointer Registers:
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To facilitate accessing both internal and external data memory, two banks of 16-bit Data Pointer
Registers are provided: DP0 at SFR address locations 82H-83H and DP1 at 84H and 85H. Bit
DPS = 0 in SFR AUXR1 selects DP0 and DPS = 1 selects DP1. The user should ALWAYS
initialize the DPS bit to the appropriate value before accessing the respective Data Pointer
Register.
Power Off Flag:
The Power Off Flag (POF) is located at bit 4 (PCON.4) in the PCON SFR. POF is set to “1”
during power up. It can be set and rest under software control and is not affected by reset.

Memory Organization
MCS-51 devices have a separate address space for Program and Data Memory. Up to 64K bytes
each of external Program and Data Memory can be addressed.
Program Memory
If the EA pin is connected to GND, all program fetches are directed to external memory. On the
AT89S52, if EA is connected to VCC, program fetches to addresses 0000H through 1FFFH are
directed to internal memory and fetches to addresses 2000H through FFFFH are to external
memory.

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Data Memory
The AT89S52 implements 256 bytes of on-chip RAM. The upper 128 bytes occupy a parallel
address space to the Special Function Registers. This means that the upper 128 bytes have the
same addresses as the SFR space but are physically separate from SFR space.
When an instruction accesses an internal location above address 7FH, the address mode used in
the instruction specifies whether the CPU accesses the upper 128 bytes of RAM or the SFR
space. Instructions which use direct addressing access the SFR space.
For example, the following direct addressing instruction accesses the SFR at location 0A0H
(which is P2).
MOV 0A0H, #data
The instructions that use indirect addressing access the upper 128 bytes of RAM. For example,
the following indirect addressing instruction, where R0 contains 0A0H, accesses the data byte at
address 0A0H, rather than P2 (whose address is 0A0H).
MOV @R0, #data
It should be noted that stack operations are examples of indirect addressing, so the upper 128
bytes of data RAM are available as stack space.

Watchdog Timer (One-time Enabled with Reset-out)
The WDT is intended as a recovery method in situations where the CPU may be subjected to
software upsets. The WDT consists of a 14-bit counter and the Watchdog Timer Reset
(WDTRST) SFR. The WDT is defaulted to disable from exiting reset. To enable the WDT, a
user must write 01EH and 0E1H in sequence to the WDTRST register (SFR location 0A6H).
When the WDT is enabled, it will increment every machine cycle while the oscillator is running.
The WDT timeout period is dependent on the external clock frequency. There is no way to
disable the WDT except through reset (either hardware reset or WDT overflow reset). When
WDT overflows, it will drive an output RESET HIGH pulse at the RST pin.
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Using the WDT
To enable the WDT, a user must write 01EH and 0E1H in sequence to the WDTRST register
(SFR location 0A6H). When the WDT is enabled, the user needs to service it regularly by
writing 01EH and 0E1H to WDTRST to avoid a WDT overflow. The 14-bit counter overflows
when it reaches 16383 (3FFFH) and this will reset the device. When the WDT is enabled, it will
increment every machine cycle while the oscillator is running. This means the user must reset the
WDT at least for every 16383 machine cycles.
To reset the WDT, the user must write 01EH and 0E1H to WDTRST. WDTRST is a write-only
register. The WDT counter cannot be read or written. When WDT overflows, it will generate an
output RESET pulse at the RST pin. The RESET pulse duration is 98xTOSC, where TOSC =
1/FOSC. To make the best use of the WDT, it should be serviced in those sections of code that
will periodically be executed within the time required to prevent a WDT reset.

WDT during Power-down and Idle
In Power down mode the oscillator stops, which means the WDT also stops. Thus the user does
not need to service the WDT in Power down mode.
There are two methods of exiting Power down mode:
1. By a hardware reset or
2. By a level-activated external interrupt which is enabled prior to entering Power down
mode.
When Power-down is exited with hardware reset, servicing the WDT should occur as it normally
does whenever the AT89S52 is reset. Exiting Power down with an interrupt is significantly
different.

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The interrupt is held low long enough for the oscillator to stabilize. When the interrupt is brought
high, the interrupt is serviced. To prevent the WDT from resetting the device while the interrupt
pin is held low, the WDT is not started until the interrupt is pulled high. It is suggested that the
WDT be reset during the interrupt service for the interrupt used to exit Power down mode.
To ensure that the WDT does not overflow within a few states of exiting Power down, it is best
to reset the WDT just before entering Power down mode.
Before going into the IDLE mode, the WDIDLE bit in SFR AUXR is used to determine whether
the WDT continues to count if enabled. The WDT keeps counting during IDLE (WDIDLE bit =
0) as the default state. To prevent the WDT from resetting the AT89S52 while in IDLE mode,
the user should always set up a timer that will periodically exit IDLE, service the WDT and
reenter IDLE mode. With WDIDLE bit enabled, the WDT will stop to count in IDLE mode and
resumes the count upon exit from IDLE.

UART
The Atmel 8051 Microcontrollers implement three general purpose, 16-bit timers/ counters.
They are identified as Timer 0, Timer 1 and Timer 2 and can be independently configured to
operate in a variety of modes as a timer or as an event counter. When operating as a timer, the
timer/counter runs for a programmed length of time and then issues an interrupt request. When
operating as a counter, the timer/counter counts negative transitions on an external pin. After a
preset number of counts, the counter issues an interrupt request. The various operating modes of
each timer/counter are described in the following sections.

A basic operation consists of timer registers THx and TLx (x= 0, 1) connected in cascade
to form a 16-bit timer. Setting the run control bit (TRx) in TCON register turns the timer on by
allowing the selected input to increment TLx. When TLx overflows it increments THx; when
THx overflows it sets the timer overflow flag (TFx) in TCON register. Setting the TRx does not
clear the THx and TLx timer registers. Timer registers can be accessed to obtain the current
count or to enter preset values. They can be read at any time but TRx bit must be cleared to
preset their values, otherwise the behavior of the timer/counter is unpredictable.

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The C/T control bit (in TCON register) selects timer operation or counter operation, by selecting
the divided-down peripheral clock or external pin Tx as the source for the counted signal. TRx
bit must be cleared when changing the mode of operation, otherwise the behavior of the
timer/counter is unpredictable. For timer operation (C/Tx# = 0), the timer register counts the
divided-down peripheral clock. The timer register is incremented once every peripheral cycle (6
peripheral clock periods). The timer clock rate is FPER / 6, i.e. FOSC / 12 in standard mode or
FOSC / 6 in X2 mode. For counter operation (C/Tx# = 1), the timer register counts the negative
transitions on the Tx external input pin. The external input is sampled every peripheral cycle.
When the sample is high in one cycle and low in the next one, the counter is incremented.

Since it takes 2 cycles (12 peripheral clock periods) to recognize a negative transition, the
maximum count rate is FPER / 12, i.e. FOSC / 24 in standard mode or FOSC / 12 in X2 mode.
There are no restrictions on the duty cycle of the external input signal, but to ensure that a given
level is sampled at least once before it changes, it should be held for at least one full peripheral
cycle. In addition to the “timer” or “counter” selection, Timer 0 and Timer 1 have four operating
modes from which to select which are selected by bit-pairs (M1, M0) in TMOD. Modes 0, 1and
2 are the same for both timer/counters. Mode 3 is different.
The four operating modes are described below. Timer 2, has three modes of operation: „capture‟,
„auto-reload‟ and „baud rate generator‟.

Timer 0
Timer 0 functions as either a timer or event counter in four modes of operation. Timer 0 is
controlled by the four lower bits of the TMOD register and bits 0, 1, 4 and 5 of the TCON
register. TMOD register selects the method of timer gating (GATE0), timer or counter operation
(T/C0#) and mode of operation (M10 and M00). The TCON register provides timer 0 control
functions: overflow flag (TF0), run control bit (TR0), interrupt flag (IE0) and interrupt type
control bit (IT0).
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For normal timer operation (GATE0= 0), setting TR0 allows TL0 to be incremented by the
selected input. Setting GATE0 and TR0 allows external pin INT0# to control timer operation.

Timer 0 overflow (count rolls over from all 1s to all 0s) sets TF0 flag, generating an interrupt
request. It is important to stop timer/counter before changing mode.
Mode 0 (13-bit Timer)
Mode 0 configures timer 0 as a 13-bit timer which is set up as an 8-bit timer (TH0 register) with
a modulo-32 prescaler implemented with the lower five bits of the TL0 register. The upper three
bits of TL0 register are indeterminate and should be ignored. Prescaler overflow increments the
TH0 register.
As the count rolls over from all 1‟s to all 0‟s, it sets the timer interrupt flag TF0. The counted
input is enabled to the Timer when TR0 = 1 and either GATE = 0 or INT0 = 1. (Setting GATE =
1 allows the Timer to be controlled by external input INT0, to facilitate pulse width
measurements). TR0 is a control bit in the Special Function register TCON. GATE is in TMOD.

The 13-bit register consists of all 8 bits of TH0 and the lower 5 bits of TL0. The upper 3
bits of TL0 are indeterminate and should be ignored. Setting the run flag (TR0) does not
clear the registers.

Mode 0 operation is the same for Timer 0 as for Timer 1. There are two different GATE bits, one
for Timer 1 (TMOD.7) and one for Timer 0 (TMOD.3).

Timer/Counter x (x = 0 or 1) in Mode 0

29

Mode 1 (16-bit Timer)
Mode 1 is the same as Mode 0, except that the Timer register is being run with all 16 bits. Mode
1 configures timer 0 as a 16-bit timer with the TH0 and TL0 registers connected in cascade. The
selected input increments the TL0 register.
Timer/Counter x (x = 0 or 1) in Mode 1

Mode 2 (8-bit Timer with Auto-Reload)
Mode 2 configures timer 0 as an 8-bit timer (TL0 register) that automatically reloads from the
TH0 register. TL0 overflow sets TF0 flag in the TCON register and reloads TL0 with the
contents of TH0, which is preset by software.

When the interrupt request is serviced, hardware clears TF0. The reload leaves TH0 unchanged.
The next reload value may be changed at any time by writing it to the TH0 register. Mode 2
operation is the same for Timer/Counter 1.

Timer/Counter x (x = 0 or 1) in Mode 2

30

Mode 3 (Two 8-bit Timers)
Mode 3 configures timer 0 so that registers TL0 and TH0 operate as separate 8-bit timers. This
mode is provided for applications requiring an additional 8-bit timer or counter. TL0 uses the
timer 0 control bits C/T0# and GATE0 in the TMOD register, and TR0 and TF0 in the TCON
register in the normal manner. TH0 is locked into a timer function (counting FPER /6) and takes
over use of the timer 1 interrupt (TF1) and run control (TR1) bits. Thus, operation of timer 1 is
restricted when timer 0 is in mode 3.

Timer/Counter 0 in Mode 3: Two 8-bit Counters

Timer 1
Timer 1 is identical to timer 0, except for mode 3, which is a hold-count mode. The following
comments help to understand the differences:
• Timer 1 functions as either a timer or event counter in three modes of operation. Timer
1‟s mode 3 is a hold-count mode.
• Timer 1 is controlled by the four high-order bits of the TMOD register and bits 2, 3, 6 and 7 of
the TCON register. The TMOD register selects the method of timer gating (GATE1), timer or
counter operation (C/T1#) and mode of operation (M11 and M01). The TCON register provides
timer 1 control functions: overflow flag (TF1), run control bit (TR1), interrupt flag (IE1) and
interrupt type control bit (IT1).
• Timer 1 can serve as the baud rate generator for the serial port. Mode 2 is best suited for this
purpose.
31

• For normal timer operation (GATE1 = 0), setting TR1 allows TL1 to be incremented by the
selected input. Setting GATE1 and TR1 allows external pin INT1# to control timer operation.
• Timer 1 overflow (count rolls over from all 1s to all 0s) sets the TF1 flag generating an
interrupt request.
• When timer 0 is in mode 3, it uses timer 1‟s overflow flag (TF1) and run control bit (TR1). For
this situation, use timer 1 only for applications that do not require an interrupt (such as a baud
rate generator for the serial port) and switch timer 1 in and out of mode 3 to turn it off and on.
• It is important to stop timer/counter before changing modes.

Mode 0 (13-bit Timer)
Mode 0 configures Timer 1 as a 13-bit timer, which is set up as an 8-bit timer (TH1 register)
with a modulo-32 prescaler implemented with the lower 5 bits of the TL1 register. The upper 3
bits of the TL1 register are ignored. Prescaler overflow increments the TH1 register.

Mode 1 (16-bit Timer)
Mode 1 configures Timer 1 as a 16-bit timer with the TH1 and TL1 registers connected
in cascade. The selected input increments the TL1 register.

Mode 2 (8-bit Timer with Auto Reload)
Mode 2 configures Timer 1 as an 8-bit timer (TL1 register) with automatic reload from the TH1
register on overflow. TL1 overflow sets the TF1 flag in the TCON register and reloads TL1 with
the contents of TH1, which is preset by software. The reload leaves TH1 unchanged.
Mode 3 (Halt)
Placing Timer 1 in mode 3 causes it to halt and hold its count. This can be used to halt
Timer 1 when TR1 run control bit is not available i.e., when Timer 0 is in mode 3.

Timer 2
Timer 2 is a 16-bit Timer/Counter that can operate as either a timer or an event counter. The type
of operation is selected by bit C/T2 in the SFR T2CON. Timer 2 has three operating modes:
capture, auto-reload (up or down counting), and baud rate generator. The modes are selected by
32

bits in T2CON. Timer 2 consists of two 8-bit registers, TH2 and TL2. In the Timer function, the
TL2 register is incremented every machine cycle. Since a machine cycle consists of 12 oscillator
periods, the count rate is 1/12 of the oscillator frequency.

In the Counter function, the register is incremented in response to a 1-to-0 transition at its
corresponding external input pin, T2. In this function, the external input is sampled during S5P2
of every machine cycle. When the samples show a high in one cycle and a low in the next cycle,
the count is incremented. The new count value appears in the register during S3P1 of the cycle
following the one in which the transition was detected. Since two machine cycles (24 oscillator
periods) are required to recognize a 1-to-0 transition, the maximum count rate is 1/24 of the
oscillator frequency. To ensure that a given level is sampled at least once before it changes, the
level should be held for at least one full machine cycle.

Capture Mode
In the capture mode, two options are selected by bit EXEN2 in T2CON. If EXEN2 = 0, Timer 2
is a 16-bit timer or counter which upon overflow sets bit TF2 in T2CON. This bit can then be
used to generate an interrupt. If EXEN2 = 1, Timer 2 performs the same operation, but a 1-to-0
transition at external input T2EX also causes the current value in TH2 and TL2 to be captured
into RCAP2H and RCAP2L, respectively. In addition, the transition at T2EX causes bit EXF2 in
T2CON to be set. The EXF2 bit, like TF2, can generate an interrupt.

33

Timer in Capture Mode

Auto-reload (Up or Down Counter)
Timer 2 can be programmed to count up or down when configured in its 16-bit auto-reload
mode. This feature is invoked by the DCEN (Down Counter Enable) bit located in the SFR
T2MOD. Upon reset, the DCEN bit is set to 0 so that timer 2 will default to count up. When
DCEN is set, Timer 2 can count up or down, depending on the value of the T2EX pin.

T2MOD – Timer 2 Mode Control Register

34

The above figure shows Timer 2 automatically counting up when DCEN = 0. In this mode, two
options are selected by bit EXEN2 in T2CON. If EXEN2 = 0, Timer 2 counts up to 0FFFFH and
then sets the TF2 bit upon overflow. The overflow also causes the timer registers to be reloaded
with the 16-bit value in RCAP2H and RCAP2L. The values in Timer in Capture ModeRCAP2H
and RCAP2L are preset by software. If EXEN2 = 1, a 16-bit reload can be triggered either by an
overflow or by a 1-to-0 transition at external input T2EX. This transition also sets the EXF2 bit.
Both the TF2 and EXF2 bits can generate an interrupt if enabled.
Setting the DCEN bit enables Timer 2 to count up or down, as shown in Figure 10-2. In this
mode, the T2EX pin controls the direction of the count. A logic 1 at T2EX makes Timer 2 count
up. The timer will overflow at 0FFFFH and set the TF2 bit. This overflow also causes the 16-bit
value in RCAP2H and RCAP2L to be reloaded into the timer registers, TH2 and TL2,
respectively.
A logic 0 at T2EX makes Timer 2 count down. The timer underflows when TH2 and TL2 equal
the values stored in RCAP2H and RCAP2L. The underflow sets the TF2 bit and causes 0FFFFH
to be reloaded into the timer registers.
The EXF2 bit toggles whenever Timer 2 overflows or underflows and can be used as a 17th bit
of resolution. In this operating mode, EXF2 does not flag an interrupt.

35

Baud Rate Generator
Timer 2 is selected as the baud rate generator by setting TCLK and/or RCLK in T2CON. Note
that the baud rates for transmit and receive can be different if Timer 2 is used for the receiver or
transmitter and Timer 1 is used for the other function. Setting RCLK and/or TCLK puts Timer 2
into its baud rate generator mode.
The baud rate generator mode is similar to the auto-reload mode, in that a rollover in TH2 causes
the Timer 2 registers to be reloaded with the 16-bit value in registers RCAP2H and RCAP2L,
which are preset by software.
The baud rates in Modes 1 and 3 are determined by Timer 2‟s overflow rate according to the
following equation.

36

The Timer can be configured for either timer or counter operation. In most applications, it is
configured for timer operation (CP/T2 = 0). The timer operation is different for Timer 2 when it
is used as a baud rate generator. Normally, as a timer, it increments every machine cycle (at 1/12
the oscillator frequency). As a baud rate generator, however, it increments every state time (at
1/2 the oscillator frequency). The baud rate formula is given below.

Where (RCAP2H, RCAP2L) is the content of RCAP2H and RCAP2L taken as a 16-bit unsigned
integer.
Timer 2 as a baud rate generator is shown in the below figure. This figure is valid only if RCLK
or TCLK = 1 in T2CON. Note that a rollover in TH2 does not set TF2 and will not generate an
interrupt. Note too, that if EXEN2 is set, a 1-to-0 transition in T2EX will set EXF2 but will not
cause a reload from (RCAP2H, RCAP2L) to (TH2, TL2). Thus, when Timer 2 is in use as a baud
rate generator, T2EX can be used as an extra external interrupt.
It should be noted that when Timer 2 is running (TR2 = 1) as a timer in the baud rate generator
mode, TH2 or TL2 should not be read from or written to. Under these conditions, the Timer is
incremented every state time, and the results of a read or write may not be accurate. The RCAP2
registers may be read but should not be written to, because a write might overlap a reload and
cause write and/or reload errors. The timer should be turned off (clear TR2) before accessing the
Timer 2 or RCAP2 registers.

37

Timer 2 in Baud Rate Generator Mode

38

Programmable Clock Out
A 50% duty cycle clock can be programmed to come out on P1.0, as shown in the below figure.
This pin, besides being a regular I/O pin, has two alternate functions. It can be programmed to
input the external clock for Timer/Counter 2 or to output a 50% duty cycle clock ranging from
61 Hz to 4 MHz (for a 16-MHz operating frequency).

Timer 2 in Clock-Out Mode
To configure the Timer/Counter 2 as a clock generator, bit C/T2 (T2CON.1) must be cleared and
bit T2OE (T2MOD.1) must be set. Bit TR2 (T2CON.2) starts and stops the timer. The clock-out
frequency depends on the oscillator frequency and the reload value of Timer 2 capture registers
(RCAP2H, RCAP2L), as shown in the following equation.

39

In the clock-out mode, Timer 2 roll-overs will not generate an interrupt. This behavior is similar
to when Timer 2 is used as a baud-rate generator. It is possible to use Timer 2 as a baud-rate
generator and a clock generator simultaneously. Note, however, that the baud rate and clock-out
frequencies cannot be determined independently from one another since they both use RCAP2H
and RCAP2L.

Interrupts
The AT89S52 has a total of six interrupt vectors: two external interrupts (INT0 and INT1), three
timer interrupts (Timers 0, 1, and 2), and the serial port interrupt. These interrupts are all shown
in the below figure.
Each of these interrupt sources can be individually enabled or disabled by setting or clearing a bit
in Special Function Register IE. IE also contains a global disable bit, EA, which disables all
interrupts at once. The below table shows that bit position IE.6 is unimplemented. User software
should not write a 1 to this bit position, since it may be used in future AT89 products.
Timer 2 interrupt is generated by the logical OR of bits TF2 and EXF2 in register T2CON.
Neither of these flags is cleared by hardware when the service routine is vectored to. In fact, the
service routine may have to determine whether it was TF2 or EXF2 that generated the interrupt,
and that bit will have to be cleared in software.
The Timer 0 and Timer 1 flags, TF0 and TF1, are set at S5P2 of the cycle in which the timers
overflow. The values are then polled by the circuitry in the next cycle. However, the Timer 2
flag, TF2, is set at S2P2 and is polled in the same cycle in which the timer overflows.

40

41

Power saving modes of operation :
8051 has two power saving modes. They are:
1. Idle Mode
2. Power Down mode.
The two power saving modes are entered by setting two bits IDL and PD in the special
function register (PCON) respectively.
The structure of PCON register is as follows.
PCON:

Address 87H

The schematic diagram for 'Power down' mode and 'Idle' mode is given as follows:

Idle Mode:

Idle mode is entered by setting IDL bit to 1 (i.e., IDL=1). The clock signal is gated off to
CPU, but not to interrupt, timer and serial port functions. The CPU status is preserved
entirely. SP, PC, PSW, Accumulator and other registers maintain their data during IDLE
mode. The port pins hold their logical states they had at the time Idle was initialized.
ALE and PSEN(bar) are held at logic high levels.
42

Ways to exit Idle Mode:
1. 1. Activation of any enabled interrupt will clear PCON.0 bit and hence the Idle Mode is
exited. The program goes to the Interrupt Service Routine (ISR). After RETI is executed
at the end of ISR, the next instruction will start from the one following the instruction
that enabled the Idle Mode.
2.
3. 2. A hardware reset exits the idle mode. The CPU starts from the instruction following
the instruction that invoked the Idle mode.

Power Down Mode:

The Power Down Mode is entered by setting the PD bit to 1. The internal clock to the
entire microcontroller is stopped. However, the program is not dead. The Power down
Mode is exited (PCON.1 is cleared to 0) by Hardware Reset only. The CPU starts from
the next instruction where the Power down Mode was invoked. Port values are not
changed/ overwritten in power down mode. Vcc can be reduced to 2V in Power down
Mode. However Vcc has to be restored to normal value before Power down Mode is
exited.

Status of External Pins During Idle and Power-down Modes

43

Program Memory Lock Bits
The AT89S52 has three lock bits that can be left unprogrammed (U) or can be programmed (P)
to obtain the additional features listed in the table.

Lock Bit Protection Modes

When lock bit 1 is programmed, the logic level at the EA pin is sampled and latched during reset.
If the device is powered up without a reset, the latch initializes to a random value and holds that
value until reset is activated. The latched value of EA must agree with the current logic level at
that pin in order for the device to function properly.
Programming the Flash – Parallel Mode
The AT89S52 is shipped with the on-chip Flash memory array ready to be programmed. The
programming interface needs a high-voltage (12-volt) program enable signal and is compatible
with conventional third-party Flash or EPROM programmers.
The AT89S52 code memory array is programmed byte-by-byte.
Programming Algorithm:
Before programming the AT89S52, the address, data, and control signals should be set up
according to the “Flash Programming Modes”. To program the AT89S52, take the following
steps:

44

1. Input the desired memory location on the address lines.
2. Input the appropriate data byte on the data lines.
3. Activate the correct combination of control signals.
4. Raise EA/VPP to 12V.
5. Pulse ALE/PROG once to program a byte in the Flash array or the lock bits. The byte write
cycle is self-timed and typically takes no more than 50 µs. Repeat steps 1 through 5, changing
the address and data for the entire array or until the end of the object file is reached.

45

Data Polling:
The AT89S52 features Data Polling to indicate the end of a byte write cycle. During a write
cycle, an attempted read of the last byte written will result in the complement of the written data
on P0.7. Once the write cycle has been completed, true data is valid on all outputs, and the next
cycle may begin. Data Polling may begin any time after a write cycle has been initiated.
Ready/Busy:
The progress of byte programming can also be monitored by the RDY/BSY output signal. P3.0 is
pulled low after ALE goes high during programming to indicate BUSY. P3.0 is pulled high again
when programming is done to indicate READY.
Program Verify:
If lock bits LB1 and LB2 have not been programmed, the programmed code data can be read
back via the address and data lines for verification. The status of the individual lock bits can be
verified directly by reading them back.
Reading the Signature Bytes:
The signature bytes are read by the same procedure as a normal verification of locations 000H,
100H, and 200H, except that P3.6 and P3.7 must be pulled to a logic low. The values returned
are as follows.
(000H) = 1EH indicates manufactured by Atmel
(100H) = 52H indicates AT89S52
(200H) = 06H
Chip Erase:
In the parallel programming mode, a chip erase operation is initiated by using the proper
combination of control signals and by pulsing ALE/PROG low for a duration of 200 ns - 500 ns.

46

In the serial programming mode, a chip erase operation is initiated by issuing the Chip Erase
instruction. In this mode, chip erase is self-timed and takes about 500 ms. During chip erase, a
serial read from any address location will return 00H at the data output.

Programming the Flash – Serial Mode
The Code memory array can be programmed using the serial ISP interface while RST is pulled to
VCC. The serial interface consists of pins SCK, MOSI (input) and MISO (output). After RST is
set high, the Programming Enable instruction needs to be executed first before other operations
can be executed. Before a reprogramming sequence can occur, a Chip Erase operation is
required.
The Chip Erase operation turns the content of every memory location in the Code array into
FFH. Either an external system clock can be supplied at pin XTAL1 or a crystal needs to be
connected across pins XTAL1 and XTAL2. The maximum serial clock (SCK) frequency should
be less than 1/16 of the crystal frequency. With a 33 MHz oscillator clock, the maximum SCK
frequency is 2 MHz.

Serial Programming Algorithm
To program and verify the AT89S52 in the serial programming mode, the following sequence is
recommended:
1. Power-up sequence:
a. Apply power between VCC and GND pins.
b. Set RST pin to “H”.
If a crystal is not connected across pins XTAL1 and XTAL2, apply a 3 MHz to 33 MHz clock to
XTAL1 pin and wait for at least 10 milliseconds.

47

2. Enable serial programming by sending the Programming Enable serial
pin MOSI/P1.5. The frequency of the shift clock supplied at pin

instruction to
SCK/P1.7 needs to be less

than the CPU clock at XTAL1 divided by 16.
3. The Code array is programmed one byte at a time in either the Byte or Page mode. The write
cycle is self-timed and typically takes less than 0.5 ms at 5V.
4. Any memory location can be verified by using the Read instruction which returns the content
at the selected address at serial output MISO/P1.6.
5. At the end of a programming session, RST can be set low to commence normal device
operation.

Power-off sequence (if needed):
1. Set XTAL1 to “L” (if a crystal is not used).
2. Set RST to “L”.
3. Turn VCC power off.

Data Polling:
The Data Polling feature is also available in the serial mode. In this mode, during a write cycle
an attempted read of the last byte written will result in the complement of the MSB of the serial
output byte on MISO.
Serial Programming Instruction Set
The Instruction Set for Serial Programming follows a 4-byte protocol and is shown in the table
given below.

48

Serial Programming Instruction Set

Programming Interface – Parallel Mode
Every code byte in the Flash array can be programmed by using the appropriate combination of
control signals. The write operation cycle is self-timed and once initiated, will automatically time
itself to completion.

49

Flash Programming Modes

50

After Reset signal is high, SCK should be low for at least 64 system clocks before it goes high to
clock in the enable data bytes. No pulsing of Reset signal is necessary. SCK should be no faster
than 1/16 of the system clock at XTAL1.
For Page Read/Write, the data always starts from byte 0 to 255. After the command byte and
upper address byte are latched, each byte thereafter is treated as data until all 256 bytes are
shifted in/out. Then the next instruction will be ready to be decoded.

51

4.5 GSM Technology:
Definition of GSM:
GSM (Global System for Mobile communications) is an open, digital cellular technology used
for transmitting mobile voice and data services.

GSM (Global System for Mobile communication) is a digital mobile telephone system that is
widely used in Europe and other parts of the world. GSM uses a variation of Time Division
Multiple Access (TDMA) and is the most widely used of the three digital wireless telephone
technologies (TDMA, GSM, and CDMA). GSM digitizes and compresses data, then sends it
down a channel with two other streams of user data, each in its own time slot. It operates at
either the 900 MHz or 1,800 MHz frequency band. It supports voice calls and data transfer
speeds of up to 9.6 kbit/s, together with the transmission of SMS (Short Message Service).

History
In 1982, the European Conference of Postal and Telecommunications Administrations (CEPT)
created the Group Special Mobile (GSM) to develop a standard for a mobile telephone system
that could be used across Europe. In 1987, a memorandum of understanding was signed by 13
countries to develop a common cellular telephone system across Europe.

Finally the system

created by SINTEF lead by Torleiv Maseng was selected.

In 1989, GSM responsibility was transferred to the European Telecommunications Standards
Institute (ETSI) and phase I of the GSM specifications were published in 1990. The first GSM
network was launched in 1991 by Radiolinja in Finland with joint technical infrastructure
maintenance from Ericsson.

By the end of 1993, over a million subscribers were using GSM phone networks being operated
by 70 carriers across 48 countries. As of the end of 1997, GSM service was available in more
than 100 countries and has become the de facto standard in Europe and Asia.

52

GSM Frequencies
GSM networks operate in a number of different frequency ranges (separated into GSM
frequency ranges for 2G and UMTS frequency bands for 3G). Most 2G GSM networks operate
in the 900 MHz or 1800 MHz bands. Some countries in the Americas (including Canada and the
United States) use the 850 MHz and 1900 MHz bands because the 900 and 1800 MHz frequency
bands were already allocated. Most 3G GSM networks in Europe operate in the 2100 MHz
frequency band. The rarer 400 and 450 MHz frequency bands are assigned in some countries
where these frequencies were previously used for first-generation systems.

GSM-900 uses 890–915 MHz to send information from the mobile station to the base station
(uplink) and 935–960 MHz for the other direction (downlink), providing 124 RF channels
(channel numbers 1 to 124) spaced at 200 kHz. Duplex spacing of 45 MHz is used. In some
countries the GSM-900 band has been extended to cover a larger frequency range. This 'extended
GSM', E-GSM, uses 880–915 MHz (uplink) and 925–960 MHz (downlink), adding 50 channels
(channel numbers 975 to 1023 and 0) to the original GSM-900 band.

Time division multiplexing is used to allow eight full-rate or sixteen half-rate speech channels
per radio frequency channel. There are eight radio timeslots (giving eight burst periods) grouped
into what is called a TDMA frame. Half rate channels use alternate frames in the same timeslot.
The channel data rate for all 8 channels is 270.833 Kbit/s, and the frame duration is 4.615 ms.

The transmission power in the handset is limited to a maximum of 2 watts in GSM850/900 and 1
watt in GSM1800/1900. GSM operates in the 900MHz and 1.8GHz bands in Europe and the
1.9GHz and 850MHz bands in the US. The 850MHz band is also used for GSM and 3G in
Australia, Canada and many South American countries. By having harmonized spectrum across
most of the globe, GSM‟s international roaming capability allows users to access the same
services when travelling abroad as at home. This gives consumers seamless and same number
connectivity in more than 218 countries.

53

Terrestrial GSM networks now cover more than 80% of the world‟s population. GSM satellite
roaming has also extended service access to areas where terrestrial coverage is not available.

Mobile Telephony Standards

1G
The first generation of mobile telephony (written 1G) operated using analogue communications
and portable devices that were relatively large. It used primarily the following standards:


AMPS (Advanced Mobile Phone System), which appeared in 1976 in the United States,
was the first cellular network standard. It was used primarily in the Americas, Russia and
Asia. This first-generation analogue network had weak security mechanisms which
allowed hacking of telephones lines.



TACS (Total Access Communication System) is the European version of the AMPS
model. Using the 900 MHz frequency band, this system was largely used in England and
then in Asia (Hong-Kong and Japan).



ETACS (Extended Total Access Communication System) is an improved version of the
TACS standard developed in the United Kingdom that uses a larger number of
communication channels.

The first-generation cellular networks were made obsolete by the appearance of an entirely
digital second generation.

Second Generation of Mobile Networks (2G)
54

The second generation of mobile networks marked a break with the first generation of cellular
telephones by switching from analogue to digital. The main 2G mobile telephony standards are:


GSM (Global System for Mobile communications) is the most commonly used standard
in Europe at the end of the 20th century and supported in the United States. This standard
uses the 900 MHz and 1800 MHz frequency bands in Europe. In the United States,
however, the frequency band used is the 1900 MHz band. Portable telephones that are
able to operate in Europe and the United States are therefore called tri-band.



CDMA (Code Division Multiple Access) uses a spread spectrum technique that allows a
radio signal to be broadcast over a large frequency range.



TDMA (Time Division Multiple Access) uses a technique of time division of
communication channels to increase the volume of data transmitted simultaneously.
TDMA technology is primarily used on the American continent, in New Zealand and in
the Asia-Pacific region.

With the 2G networks, it is possible to transmit voice and low volume digital data, for example
text messages (SMS, for Short Message Service) or multimedia messages (MMS, for Multimedia
Message Service). The GSM standard allows a maximum data rate of 9.6 kbps.

Extensions have been made to the GSM standard to improve throughput. One of these is
the GPRS (General Packet Radio System) service which allows theoretical data rates on the
order of 114 Kbit/s but with throughput closer to 40 Kbit/s in practice. As this technology does
not fit within the "3G" category, it is often referred to as 2.5G

The EDGE (Enhanced Data Rates for Global Evolution) standard, billed as 2.75G, quadruples
the throughput improvements of GPRS with its theoretical data rate of 384 Kbps, thereby
allowing the access for multimedia applications. In reality, the EDGE standard allows maximum
theoretical data rates of 473 Kbit/s, but it has been limited in order to comply with the IMT-2000
(International Mobile Telecommunications-2000) specifications from the ITU (International
Telecommunications Union).
55

3G
The IMT-2000 (International Mobile Telecommunications for the year 2000) specifications from
the International Telecommunications Union (ITU) defined the characteristics of 3G (third
generation of mobile telephony). The most important of these characteristics are:
1. High transmission data rate.
2. 144 Kbps with total coverage for mobile use.
3. 384 Kbps with medium coverage for pedestrian use.
4. 2 Mbps with reduced coverage area for stationary use.
5. World compatibility.
6. Compatibility of 3rd generation mobile services with second generation networks.

3G offers data rates of more than 144 Kbit/s, thereby allowing the access to multimedia uses
such as video transmission, video-conferencing or high-speed internet access. 3G networks use
different frequency bands than the previous networks: 1885-2025 MHz and 2110-2200 MHz.
The main 3G standard used in Europe is called UMTS (Universal Mobile Telecommunications
System) and uses WCDMA (Wideband Code Division Multiple Access) encoding. UMTS
technology uses 5 MHz bands for transferring voice and data, with data rates that can range from
384 Kbps to 2 Mbps. HSDPA (High Speed Downlink Packet Access) is a third generation mobile
telephony protocol, (considered as "3.5G"), which is able to reach data rates on the order of 8 to
10 Mbps. HSDPA technology uses the 5 GHz frequency band and uses WCDMA encoding.

Introduction to the GSM Standard
The GSM (Global System for Mobile communications) network is at the start of the 21st century,
the most commonly used mobile telephony standard in Europe. It is called as Second Generation
(2G) standard because communications occur in an entirely digital mode, unlike the first
generation of portable telephones.

When it was first standardized in 1982, it was called as Group Special Mobile and later, it
became an international standard called "Global System for Mobile communications" in 1991.
56

In Europe, the GSM standard uses the 900 MHz and 1800 MHz frequency bands. In the United
States, however, the frequency band used is the 1900 MHz band. For this reason, portable
telephones that are able to operate in both Europe and the United States are called tri-band while
those that operate only in Europe are called bi-band.
The GSM standard allows a maximum throughput of 9.6 kbps which allows transmission of
voice and low-volume digital data like text messages (SMS, for Short Message Service) or
multimedia messages (MMS, for Multimedia Message Service).

GSM Standards:
GSM uses narrowband TDMA, which allows eight simultaneous calls on the same radio
frequency.

There are three basic principles in multiple access, FDMA (Frequency Division Multiple
Access), TDMA (Time Division Multiple Access), and CDMA (Code Division Multiple
Access). All three principles allow multiple users to share the same physical channel. But the
two competing technologies differ in the way user sharing the common resource.

TDMA allows the users to share the same frequency channel by dividing the signal into different
time slots. Each user takes turn in a round robin fashion for transmitting and receiving over the
channel. Here, users can only transmit in their respective time slot.

CDMA uses a spread spectrum technology that is it spreads the information contained in a
particular signal of interest over a much greater bandwidth than the original signal. Unlike
TDMA, in CDMA several users can transmit over the channel at the same time.

TDMA in brief:
In late1980‟s, as a search to convert the existing analog network to digital as a means to improve
capacity, the cellular telecommunications industry association chose TDMA over FDMA.

57

Time Division Multiplex Access is a type of multiplexing where two or more channels of
information are transmitted over the same link by allocating a different time interval for the
transmission of each channel. The most complex implementation using TDMA principle is of
GSM‟s (Global System for Mobile communication). To reduce the effect of co-channel
interference, fading and multipath, the GSM technology can use frequency hoping, where a call
jumps from one channel to another channel in a short interval.

TDMA systems still rely on switch to determine when to perform a handoff. Handoff occurs
when a call is switched from one cell site to another while travelling. The TDMA handset
constantly monitors the signals coming from other sites and reports it to the switch without
caller‟s awareness. The switch then uses this information for making better choices for handoff
at appropriate times. TDMA handset performs hard handoff, i.e., whenever the user moves from
one site to another, it breaks the connection and then provides a new connection with the new
site.

Advantages of TDMA:
There are lots of advantages of TDMA in cellular technologies.
1. It can easily adapt to transmission of data as well as voice communication.
58

2. It has an ability to carry 64 kbps to 120 Mbps of data rates. This allows the operator to do
services like fax, voice band data and SMS as well as bandwidth intensive application
such as multimedia and video conferencing.
3. Since TDMA technology separates users according to time, it ensures that there will be
no interference from simultaneous transmissions.
4. It provides users with an extended battery life, since it transmits only portion of the time
during conversations. Since the cell size grows smaller, it proves to save base station
equipment, space and maintenance.
TDMA is the most cost effective technology to convert an analog system to digital.

Disadvantages of TDMA:
One major disadvantage using TDMA technology is that the users has a predefined time slot.
When moving from one cell site to other, if all the time slots in this cell are full the user might be
disconnected. Likewise, if all the time slots in the cell in which the user is currently in are
already occupied, the user will not receive a dial tone.

The second problem in TDMA is that it is subjected to multipath distortion. To overcome this
distortion, a time limit can be used on the system. Once the time limit is expired, the signal is
ignored.

The concept of cellular network
Mobile telephone networks are based on the concept of cells, circular zones that overlap to cover
a geographical area.

59

Cellular networks are based on the use of a central transmitter-receiver in each cell, called a
"base station" (or Base Transceiver Station, written BTS). The smaller the radius of a cell, the
higher is the available bandwidth. So, in highly populated urban areas, there are cells with a
radius of a few hundred meters, while huge cells of up to 30 kilometers provide coverage in rural
areas.

In a cellular network, each cell is surrounded by 6 neighbouring cells (thus a cell is generally
drawn as a hexagon). To avoid interference, adjacent cells cannot use the same frequency. In
practice, two cells using the same frequency range must be separated by a distance of two to
three times the diameter of the cell.

Architecture of the GSM Network
In a GSM network, the user terminal is called a mobile station. A mobile station is made up of
a SIM (Subscriber Identity Module) card allowing the user to be uniquely identified and a
mobile terminal.
The

terminals

(devices)

are

identified

by

a

unique

15-digit

identification

number

called IMEI (International Mobile Equipment Identity). Each SIM card also has a unique (and
secret) identification number called IMSI (International Mobile Subscriber Identity). This code
can be protected using a 4-digit key called a PIN code.
The SIM card therefore allows each user to be identified independently of the terminal used
during communication with a base station. Communications occur through a radio link (air
interface) between a mobile station and a base station.

60

All the base stations of a cellular network are connected to a base station controller (BSC)
which is responsible for managing distribution of the resources. The system consisting of the
base

station

controller

and

its

connected

base

stations is called

the Base

Station

Subsystem (BSS).

Finally, the base station controllers are themselves physically connected to the Mobile
Switching Centre (MSC), managed by the telephone network operator, which connects them to
the public telephone network and the Internet. The MSC belongs to a Network Station
Subsystem (NSS), which is responsible for managing user identities, their location and
establishment of communications with other subscribers. The MSC is generally connected to
databases that provide additional functions:

1. The Home Location Register (HLR) is a database containing information (geographic
position, administrative information etc.) of the subscribers registered in the area of the
switch (MSC).
61

2. The Visitor Location Register (VLR) is a database containing information of users
other than the local subscribers. The VLR retrieves the data of a new user from the HLR
of the user's subscriber zone. The data is maintained as long as the user is in the zone and
is deleted when the user leaves or after a long period of inactivity (terminal off).
3. The Equipment Identify Register (EIR) is a database listing the mobile terminals.
4. The Authentication Centre (AUC) is responsible for verifying user identities.
5. The cellular network formed in this way is designed to support mobility via management
of handovers (movements from one cell to another).

Finally, GSM networks support the concept of roaming i.e., movement from one operator
network to another.

Introduction to Modem:

Modem stands for modulator-demodulator.
A modem is a device or program that enables a computer to transmit data over telephone or cable
lines. Computer information is stored digitally, whereas information transmitted over telephone
lines is transmitted in the form of analog waves. A modem converts between these two forms.

Fortunately, there is one standard interface for connecting external modems to computers called
RS-232. Consequently, any external modem can be attached to any computer that has an RS-232
port, which almost all personal computers have. There are also modems that come as an
expansion board that can be inserted into a vacant expansion slot. These are sometimes called
onboard or internal modems.
62

While the modem interfaces are standardized, a number of different protocols for formatting data
to be transmitted over telephone lines exist. Some, like CCITT V.34 are official standards, while
others have been developed by private companies. Most modems have built-in support for the
more common protocols at slow data transmission speeds at least, most modems can
communicate with each other. At high transmission speeds, however, the protocols are less
standardized.

Apart from the transmission protocols that they support, the following characteristics distinguish
one modem from another:
 Bps: How fast the modem can transmit and receive data. At slow rates, modems are
measured in terms of baud rates. The slowest rate is 300 baud (about 25 cps). At higher
speeds, modems are measured in terms of bits per second (bps). The fastest modems run
at 57,600 bps, although they can achieve even higher data transfer rates by compressing
the data. Obviously, the faster the transmission rate, the faster the data can be sent and
received. It should be noted that the data cannot be received at a faster rate than it is
being sent.
 Voice/data: Many modems support a switch to change between voice and data modes. In
data mode, the modem acts like a regular modem. In voice mode, the modem acts like a
regular telephone. Modems that support a voice/data switch have a built-in loudspeaker
and microphone for voice communication.
 Auto-answer: An auto-answer modem enables the computer to receive calls in the
absence of the operator.
 Data compression: Some modems perform data compression, which enables them to
send data at faster rates. However, the modem at the receiving end must be able to
decompress the data using the same compression technique.
 Flash memory: Some modems come with flash memory rather than conventional ROM
which means that the communications protocols can be easily updated if necessary.
 Fax capability: Most modern modems are fax modems, which mean that they can send
and receive faxes.

63

GSM Modem:
A GSM modem is a wireless modem that works with a GSM wireless network. A wireless
modem behaves like a dial-up modem. The main difference between them is that a dial-up
modem sends and receives data through a fixed telephone line while a wireless modem sends and
receives data through radio waves.

A GSM modem can be an external device or a PC Card / PCMCIA Card. Typically, an external
GSM modem is connected to a computer through a serial cable or a USB cable. A GSM modem
in the form of a PC Card / PCMCIA Card is designed for use with a laptop computer. It should
be inserted into one of the PC Card / PCMCIA Card slots of a laptop computer.
Like a GSM mobile phone, a GSM modem requires a SIM card from a wireless carrier in order
to operate.

A SIM card contains the following information:


Subscriber telephone number (MSISDN)



International subscriber number (IMSI, International Mobile Subscriber Identity)



State of the SIM card



Service code (operator)



Authentication key



PIN (Personal Identification Code)
64



PUK (Personal Unlock Code)

Computers use AT commands to control modems. Both GSM modems and dial-up modems
support a common set of standard AT commands. In addition to the standard AT commands,
GSM modems support an extended set of AT commands. These extended AT commands are
defined in the GSM standards. With the extended AT commands, the following operations can
be performed:


Reading, writing and deleting SMS messages.



Sending SMS messages.



Monitoring the signal strength.



Monitoring the charging status and charge level of the battery.



Reading, writing and searching phone book entries.

65

The number of SMS messages that can be processed by a GSM modem per minute is very low
i.e., about 6 to 10 SMS messages per minute.

Introduction to AT Commands
AT commands are instructions used to control a modem. AT is the abbreviation of ATtention.
Every command line starts with "AT" or "at". That's the reason, modem commands are called AT
commands. Many of the commands that are used to control wired dial-up modems, such as ATD
(Dial), ATA (Answer), ATH (Hook control) and ATO (Return to online data state) are also
supported by GSM modems and mobile phones.

Besides this common AT command set, GSM modems and mobile phones support an AT
command set that is specific to the GSM technology, which includes SMS-related commands
like AT+CMGS (Send SMS message), AT+CMSS (Send SMS message from storage),
AT+CMGL (List SMS messages) and AT+CMGR (Read SMS messages).
It should be noted that the starting "AT" is the prefix that informs the modem about the start of a
command line. It is not part of the AT command name. For example, D is the actual AT
command name in ATD and +CMGS is the actual AT command name in AT+CMGS.

Some of the tasks that can be done using AT commands with a GSM modem or mobile phone
are listed below:
 Get basic information about the mobile phone or GSM modem. For example, name of
manufacturer (AT+CGMI), model number (AT+CGMM), IMEI number (International
Mobile Equipment Identity) (AT+CGSN) and software version (AT+CGMR).
 Get basic information about the subscriber. For example, MSISDN (AT+CNUM) and
IMSI number (International Mobile Subscriber Identity) (AT+CIMI).
 Get the current status of the mobile phone or GSM/GPRS modem. For example, mobile
phone activity status (AT+CPAS), mobile network registration status (AT+CREG), radio
signal strength (AT+CSQ), battery charge level and battery charging status (AT+CBC).
 Establish a data connection or voice connection to a remote modem (ATD, ATA, etc).
66

 Send and receive fax (ATD, ATA, AT+F*).
 Send (AT+CMGS, AT+CMSS), read (AT+CMGR, AT+CMGL), write (AT+CMGW) or
delete (AT+CMGD) SMS messages and obtain notifications of newly received SMS
messages (AT+CNMI).
 Read (AT+CPBR), write (AT+CPBW) or search (AT+CPBF) phonebook entries.
 Perform security-related tasks, such as opening or closing facility locks (AT+CLCK),
checking whether a facility is locked (AT+CLCK) and changing passwords(AT+CPWD).
(Facility lock examples: SIM lock [a password must be given to the SIM card every time
the mobile phone is switched on] and PH-SIM lock [a certain SIM card is associated with
the mobile phone. To use other SIM cards with the mobile phone, a password must be
entered.])
 Control the presentation of result codes / error messages of AT commands. For example,
the user can control whether to enable certain error messages (AT+CMEE) and whether
error messages should be displayed in numeric format or verbose format (AT+CMEE=1
or AT+CMEE=2).
 Get or change the configurations of the mobile phone or GSM/GPRS modem. For
example, change the GSM network (AT+COPS), bearer service type (AT+CBST), radio
link protocol parameters (AT+CRLP), SMS center address (AT+CSCA) and storage of
SMS messages (AT+CPMS).
 Save and restore configurations of the mobile phone or GSM/GPRS modem. For
example, save (AT+CSAS) and restore (AT+CRES) settings related to SMS messaging
such as the SMS center address.

It should be noted that the mobile phone manufacturers usually do not implement all AT
commands, command parameters and parameter values in their mobile phones. Also, the
behavior of the implemented AT commands may be different from that defined in the standard.
In general, GSM modems, designed for wireless applications, have better support of AT
commands than ordinary mobile phones.

67

Basic concepts of SMS technology
1. Validity Period of an SMS Message
An SMS message is stored temporarily in the SMS center if the recipient mobile phone is offline.
It is possible to specify the period after which the SMS message will be deleted from the SMS
center so that the SMS message will not be forwarded to the recipient mobile phone when it
becomes online. This period is called the validity period.

A mobile phone should have a menu option that can be used to set the validity period. After
setting it, the mobile phone will include the validity period in the outbound SMS messages
automatically.

2. Message Status Reports
Sometimes the user may want to know whether an SMS message has reached the recipient
mobile phone successfully. To get this information, you need to set a flag in the SMS message to
notify the SMS center that a status report is required about the delivery of this SMS message.
The status report is sent to the user mobile in the form of an SMS message.

A mobile phone should have a menu option that can be used to set whether the status report
feature is on or off. After setting it, the mobile phone will set the corresponding flag in the
outbound SMS messages for you automatically. The status report feature is turned off by default
on most mobile phones and GSM modems.

3. Message Submission Reports
After leaving the mobile phone, an SMS message goes to the SMS center. When it reaches the
SMS center, the SMS center will send back a message submission report to the mobile phone to
inform whether there are any errors or failures (e.g. incorrect SMS message format, busy SMS
center, etc). If there is no error or failure, the SMS center sends back a positive submission report
to the mobile phone. Otherwise it sends back a negative submission report to the mobile phone.
68

The mobile phone may then notify the user that the message submission was failed and what
caused the failure.
If the mobile phone does not receive the message submission report after a period of time, it
concludes that the message submission report has been lost. The mobile phone may then send the
SMS message again to the SMS center. A flag will be set in the new SMS message to inform the
SMS center that this SMS message has been sent before. If the previous message submission was
successful, the SMS center will ignore the new SMS message but send back a message
submission report to the mobile phone. This mechanism prevents the sending of the same SMS
message to the recipient multiple times.

Sometimes the message submission report mechanism is not used and the acknowledgement of
message submission is done in a lower layer.

4.Message Delivery Reports
After receiving an SMS message, the recipient mobile phone will send back a message delivery
report to the SMS center to inform whether there are any errors or failures (example causes:
unsupported SMS message format, not enough storage space, etc). This process is transparent to
the mobile user. If there is no error or failure, the recipient mobile phone sends back a positive
delivery report to the SMS center. Otherwise it sends back a negative delivery report to the SMS
center.

If the sender requested a status report earlier, the SMS center sends a status report to the sender
when it receives the message delivery report from the recipient. If the SMS center does not
receive the message delivery report after a period of time, it concludes that the message delivery
report has been lost. The SMS center then ends the SMS message to the recipient for the second
time.

Sometimes the message delivery report mechanism is not used and the acknowledgement of
message delivery is done in a lower layer.

69

4.6 Serial Communication:
The main requirements for serial communication are:
1. Microcontroller
2. PC
3. RS 232 cable
4. MAX 232 IC
5. HyperTerminal
When the pins P3.0 and P3.1 of microcontroller are set, UART which is inbuilt in the
microcontroller will be enabled to start the serial communication.
Timers:
The 8051 has two timers: Timer 0 and Timer 1. They can be used either as timers to generate a
time delay or as counters to count events happening outside the microcontroller.
Both Timer 0 and Timer 1 are 16-bit wide. Since the 8051 has an 8-bit architecture, each 16-bit
timer is accessed as two separate registers of low byte and high byte.
Lower byte register of Timer 0 is TL0 and higher byte is TH0. Similarly lower byte register of
Timer1 is TL1 and higher byte register is TH1.
TMOD (timer mode) register:
Both timers 0 and 1 use the same register TMOD to set the various operation modes. TMOD is
an 8-bit register in which the lower 4 bits are set aside for Timer 0 and the upper 4 bits for Timer
1. In each case, the lower 2 bits are used to set the timer mode and the upper 2 bits to specify the
operation.

70

GATE
Every timer has a means of starting and stopping. Some timers do this by software, some by
hardware and some have both software and hardware controls. The timers in the 8051 have both.
The start and stop of the timer are controlled by the way of software by the TR (timer start) bits
TR0 and TR1. These instructions start and stop the timers as long as GATE=0 in the TMOD
register. The hardware way of starting and stopping the timer by an external source is achieved
by making GATE=1 in the TMOD register.

C/T
Timer or counter selected. Cleared for timer operation and set for counter operation.

M1
Mode bit 1

M0
Mode bit 0

Mode Selection
M1

M0

Mode

Operating Mode

0

0

0

13-bit timer mode
8-bit timer/counter THx with TLx as 5-bit prescaler

0

1

1

16-bit timer mode
16-bit timer/counters THx and TLx are cascaded
71

1

0

2

8-bit auto reload timer/counter
THx holds a value that is to be reloaded into TLx each time
it overflows

1

1

3

Split timer mode

The mode used here to generate a time delay is MODE 2. This mode 2 is an 8-bit timer and
therefore it allows only values of 00H to FFH to be loaded into the timer‟s register TH. After TH
is loaded with the 8-bit value, the 8051 give a copy of it to TL. When the timer starts, it starts to
count up by incrementing the TL register. It counts up until it reaches its limit of FFH. When it
rolls over from FFH to 00H, it sets high the TF (timer flag). If Timer 0 is used, TF0 goes high
and if Timer 1 is used, TF1 goes high. When the TL register rolls from FFH to 0 and TF is set to
1, TL is reloaded automatically with the original value kept by the TH register.

Asynchronous and Synchronous Serial Communication
Computers transfer data in two ways: parallel and serial. In parallel data transfers, often 8 or
more lines are used to transfer data to a device that is only a few feet away. Although a lot of
data can be transferred in a short amount of time by using many wires in parallel, the distance
cannot be great. To transfer to a device located many meters away, the serial method is best
suitable.

In serial communication, the data is sent one bit at a time. The 8051 has serial communication
capability built into it, thereby making possible fast data transfer using only a few wires.

The fact that serial communication uses a single data line instead of the 8-bit data line instead of
the 8-bit data line of parallel communication not only makes it cheaper but also enables two
computers located in two different cities to communicate over the telephone.

Serial data communication uses two methods, asynchronous and synchronous. The synchronous
method transfers a block of data at a time, while the asynchronous method transfers a single byte
at a time. With synchronous communications, the two devices initially synchronize themselves to
72

each other, and then continually send characters to stay in sync. Even when data is not really
being sent, a constant flow of bits allows each device to know where the other is at any given
time. That is, each character that is sent is either actual data or an idle character. Synchronous
communications allows faster data transfer rates than asynchronous methods, because additional
bits to mark the beginning and end of each data byte are not required. The serial ports on IBMstyle

PCs

are

asynchronous

devices

and

therefore only support asynchronous serial

communications.

Asynchronous means "no synchronization", and thus does not require sending and receiving idle
characters. However, the beginning and end of each byte of data must be identified by start and
stop bits. The start bit indicates when the data byte is about to begin and the stop bit signals when
it ends. The requirement to send these additional two bits causes asynchronous communication to
be slightly slower than synchronous however it has the advantage that the processor does not
have to deal with the additional idle characters.

There are special IC chips made by many manufacturers for serial data communications. These
chips are commonly referred to as UART(universal asynchronous receiver-transmitter) and
USART(universal synchronous-asynchronous receiver-transmitter). The 8051 has a built-in
UART.

In the asynchronous method, the data such as ASCII characters are packed between a start and a
stop bit. The start bit is always one bit, but the stop bit can be one or two bits. The start bit is
always a 0 (low) and stop bit (s) is 1 (high). This is called framing.

The rate of data transfer in serial data communication is stated as bps (bits per second). Another
widely used terminology for bps is baud rate. The data transfer rate of a given computer system
depends on communication ports incorporated into that system. And in asynchronous serial data
communication, this baud rate is generally limited to 100,000bps. The baud rate is fixed to
9600bps in order to interface with the microcontroller using a crystal of 11.0592 MHz.

73

RS232 CABLE:
To allow compatibility among data communication equipment, an interfacing standard called
RS232 is used. Since the standard was set long before the advent of the TTL logic family, its
input and output voltage levels are not TTL compatible. For this reason, to connect any RS232 to
a microcontroller system, voltage converters such as MAX232 are used to convert the TTL logic
levels to the RS232 voltage levels and vice versa.

MAX 232:
Max232 IC is a specialized circuit which makes standard voltages as required by RS232
standards. This IC provides best noise rejection and very reliable against discharges and short
circuits. MAX232 IC chips are commonly referred to as line drivers.

To ensure data transfer between PC and microcontroller, the baud rate and voltage levels of
Microcontroller and PC should be the same. The voltage levels of microcontroller are logic1 and
logic 0 i.e., logic 1 is +5V and logic 0 is 0V. But for PC, RS232 voltage levels are considered
and they are: logic 1 is taken as -3V to -25V and logic 0 as +3V to +25V. So, in order to equal
these voltage levels, MAX232 IC is used. Thus this IC converts RS232 voltage levels to
microcontroller voltage levels and vice versa.

74

Interfacing max232 with microcontrolle r:

SCON (serial control) register:
The SCON register is an 8-bit register used to program the start bit, stop bit and data bits of data
framing.

SM0

SCON.7

Serial port mode specifier

SM1

SCON.6

Serial port mode specifier

SM2

SCON.5

Used for multiprocessor communication

REN

SCON.4

Set/cleared by software to enable/disable reception
75

TB8

SCON.3

Not widely used

RB8

SCON.2

Not widely used

TI

SCON.1

Transmit interrupt flag. Set by hardware at the
beginning of the stop bit in mode 1. Must be
cleared by software.

RI

SCON.0

Receive interrupt flag. Set by hardware at the
beginning of the stop bit in mode 1. Must be
cleared by software.

SM0

SM1

0

0

Serial Mode 0

0

1

Serial Mode 1, 8-bit data, 1 stop bit, 1 start bit

1

0

Serial Mode 2

1

1

Serial Mode 3

Of the four serial modes, only mode 1 is widely used. In the SCON register, when serial mode 1
is chosen, the data framing is 8 bits, 1 stop bit and 1 start bit, which makes it compatible with the
COM port of IBM/ compatible PC‟s. And the most important is serial mode 1 allows the baud
rate to be variable and is set by Timer 1 of the 8051. In serial mode 1, for each character a total
of 10 bits are transferred, where the first bit is the start bit, followed by 8 bits of data and finally
1 stop bit.

8051 Interface with any External Devices using Serial Communication:

76

4.7 L293D- Current Driver

77

Features


Wide Supply-Voltage Range: 4.5 V to 36 V



Separate Input-Logic Supply



Internal ESD Protection



Thermal Shutdown



High-Noise-Immunity Inputs



Functionally Similar to SGS L293 and SGS L293D



Output Current 1 A Per Channel (600 mA for L293D)



Peak Output Current 2 A Per Channel (1.2 A for L293D)



Output Clamp Diodes for Inductive Transient Suppression (L293D)

Description
The L293 and L293D are quadruple high-current half-H drivers. The L293 is designed to provide
bidirectional drive currents of up to 1 A at voltages from 4.5 V to 36 V. The L293D is designed
to provide bidirectional drive currents of up to 600-mA at voltages from 4.5 V to 36 V. Both
devices are designed to drive inductive loads such as relays, solenoids, dc and bipolar stepping
motors, as well as other high-current/high-voltage loads in positive-supply applications.

All inputs are TTL compatible. Each output is a complete totem-pole drive circuit, with a
Darlington transistor sink and a pseudo- Darlington source. Drivers are enabled in pairs, with
drivers 1 and 2 enabled by 1,2EN and drivers 3 and 4 enabled by 3,4EN. When an enable input is
high, the associated drivers are enabled and their outputs are active and in phase with their
inputs. When the enable input is low, those drivers are disabled and their outputs are off and in
the high-impedance state. With the proper data inputs, each pair of drivers forms a full-H (or
bridge) reversible drive suitable for solenoid or motor applications. On the L293, external highspeed output clamp diodes should be used for inductive transient suppression.

78

A VCC1 terminal, separate from VCC2, is provided for the logic inputs to minimize device
power dissipation. The L293 and L293D are characterized for operation from 0 to 70 degree
Celsius.

79

This chip contains 4 enable pins. Each enable pin corresponds to 2 inputs. Based on the input
values given, the device connected to this IC works accordingly.
L293D Interfacing with 8051:

4.8 Electric Motors:
Electric motors are used to efficiently convert electrical energy into mechanical energy.
Magnetism is the basis of their principles of operation. They use permanent magnets,
electromagnets, and exploit the magnetic properties of materials in order to create these amazing
machines.
80

There are several types of electric motors available today. The following outline gives an
overview of several popular ones. There are two main classes of motors: AC and DC. AC motors
require an alternating current or voltage source (like the power coming out of the wall outlets in
your house) to make them work. DC motors require a direct current or voltage source (like the
voltage coming out of batteries) to make them work. Universal motors can work on either type of
power. Not only is the construction of the motors different, but the means used to control the
speed and torque created by each of these motors also varies, although the principles of power
conversion are common to both.
Motors are used just about everywhere. In our house, there is a motor in the furnace for the
blower, for the intake air, in the sump well, dehumidifier, in the kitchen in the exhaust hood
above the stove, microwave fan, refrigerator compressor and cooling fan, can opener, garbage
disposer, dish washer pump, clocks, computer fans, ceiling fans, and many more items.
In industry, motors are used to move, lift, rotate, accelerate, brake, lower and spin material in
order to coat, paint, punch, plate, make or form steel, film, paper, tissue, aluminum, plastic and
other raw materials.
They range in power ratings from less than 1/100 hp to over 100,000 hp. The rotate as slowly as
0.001 rpm to over 100,000 rpm. They range in physical size from as small as the head of a pin to
the size of a locomotive engine.
What happens when a wire carrying current is within a magnetic field?

This is the Left Hand Rule for motors.

81

The first finger points in the direction of the magnetic field (first - field), which goes from the
North pole to the South pole.
The second finger points in the direction of the current in the wire (second - current).
The thumb then points in the direction the wire is thrust or pushed while in the magnetic field
(thumb - torque or thrust).
So, when a wire carrying current is perpendicular to a magnetic field, a force is created on the
wire causing it to move perpendicular to the field and direction of current. The greater the
current in the wire, or the greater the magnetic field, the faster the wire moves because of the
greater force created. If the current in the wire is parallel to the magnetic field, there will be no
force on the wire.
DC Motors

DC motors are fairly simple to understand. They are also simple to make and only require a
battery or dc supply to make them run.
A simple motor has six parts, as shown in the diagram below:







Armature or rotor
Commutator
Brushes
Axle
Field magnet
DC power supply of some sort
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An electric motor is all about magnets and magnetism: A motor uses magnets to create motion.
If you have ever played with magnets you know about the fundamental law of all magnets:
Opposites attract and likes repel. So if you have two bar magnets with their ends marked "north"
and "south," then the north end of one magnet will attract the south end of the other. On the other
hand, the north end of one magnet will repel the north end of the other (and similarly, south will
repel south). Inside an electric motor, these attracting and repelling forces create rotational
motion.

The armature (or rotor) is an electromagnet, while the field magnet is a permanent magnet (the
field magnet could be an electromagnet as well, but in most small motors it is not in order to save
power).

When you put all of these parts together, here is a complete electric motor:

83

In the above figure, the armature winding has been left out so that it is easier to see the
commutator in action. The key thing to notice is that as the armature passes through the
horizontal position, the poles of the electromagnet flip. Because of the flip, the north pole of the
electromagnet is always above the axle so it can repel the field magnet's north pole and attract
the field magnet's south pole.
Even a small electric motor contains the same pieces described above: two small permanent
magnets, a commutator, two brushes, and an electromagnet made by winding wire around a
piece of metal. Almost always, however, the rotor will have three poles rather than the two poles
as shown in this article. There are two good reasons for a motor to have three poles:


It causes the motor to have better dynamics. In a two-pole motor, if the electromagnet is
at the balance point, perfectly horizontal between the two poles of the field magnet when
the motor starts, one can imagine the armature getting "stuck" there. This never happens
in a three-pole motor.



Each time the commutator hits the point where it flips the field in a two-pole motor, the
commutator shorts out the battery (directly connects the positive and negative terminals)
for a moment. This shorting wastes energy and drains the battery needlessly. A three-pole
motor solves this problem as well.

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It is possible to have any number of poles, depending on the size of the motor and the specific
application it is being used in.
Types of Motors
Split Phase
The split phase motor is mostly used for "medium starting" applications. It has start and run
windings, both are energized when the motor is started. When the motor reaches about 75% of its
rated full load speed, the starting winding is disconnected by an automatic switch.
Uses: This motor is used where stops and starts are somewhat frequent. Common applications of
split phase motors include: fans, blowers, office machines and tools such as small saws or drill
presses where the load is applied after the motor has obtained its operating speed.
Capacitor Start
This motor has a capacitor in series with a starting winding and provides more than double the
starting torque with one third less starting current than the split phase motor. Because of this
improved starting ability, the capacitor start motor is used for loads which are hard to start. It has
good efficiency and requires starting currents of approximately five times full load current. The
capacitor and starting windings are disconnected from the circuit by an automatic switch when
the motor reaches about 75% of its rated full load speed.
Uses: Common uses include: compressors, pumps, machine tools, air conditioners, conveyors,
blowers, fans and other hard to start applications.
Horsepower & RPM
Horsepower
Electric motors are rated by horsepower, the home shop will probably utilize motors from 1/4 HP
for small tools and up to 5 HP on air compressors. Not all motors are rated the same, some are
rated under load, others as peak horsepower and hence we have 5 HP compressors with huge
motors and 5 Hp shopvacs with tiny little motors. Unfortunately all 5 HP compressor motors are
not equal in actual power either, to judge the true horsepower the easiest way is to look at the

85

amperage of the motor. Electric motors are not efficient, most have a rating of about 50% due to
factors such as heat and friction and some may be as high as 70%.
This chart will give a basic idea of the true horse power rating compared to the ampere rating.
Motors with a higher efficiency rating will draw fewer amps, for example a 5 HP motor with a
50% efficiency rating will draw about 32 amps at 230 VAC compared to about 23 amps for a
motor with a 70% rating.

A quick general calculation when looking at a motor is 1 HP = 10 amps on 110 volts and 1 HP =
5 amps on 220 volts.
RPM
The shaft on a typical shop motor will rotate at either 1725 or 3450 RPM (revolutions per
minute).
The speed of the driven machine will be determined by the size of pulleys used, for example a
3450 RPM motor can be replaced by a 1750 RPM motor if the diameter of the pulley on the
motor is doubled. The opposite is true as well but if the pulley on the 1750 RPM motor is small it
is not always possible to replace it with one half the size. It may be possible to double the pulley

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size on the driven machine if it uses a standard type of pulley, (not easily done on air
compressors for example).
Electronic speed reducers such as the ones sold for routers will not work on induction type
motors.
Phase, Voltage & Rotation
Whether or not you can use a motor will likely depend on these factors.

Single Phase
Ordinary household wiring is single phase, alternating current. Each cycle peaks and dips as
shown. To run a three phase motor a phase converter must be used, usually this is not practical, it
is often less expensive to change the motor on a machine to a single phase style.

Three Phase
This is used in industrial shops, rather than peaks and valleys the current supply is more even
because of the other two cycles each offset by 120 degrees.

Voltage
Many motors are dual voltage i.e., by simply changing the wiring configuration, they can be run
on 110 volts or 220 volts. Motors usually run better on 220 volts, especially if there is any line
loss because of having to use a long wire to reach the power supply.
Motors are available for both AC and DC current, our typical home wiring will be AC. There are
DC converters available which are used in applications where the speed of the motor is
controlled.
Rotation
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The direction the shaft rotates can be changed on most motors by switching the right wires. The
direction of rotation is usually determined by viewing the motor from the shaft end and is
designated as CW (clockwise) or CCW (counter-clockwise).

Inside the Wipers
The wipers combine two mechanical technologies to perform their task
1.

A combination electric motor and worm gear reduction provides power to the wipers.

2.

A neat linkage converts the rotational output of the motor into the back-and-forth motion
of the wipers.

On any gear, the ratio is determined by the distances from the center of the gear to the
point of contact. For instance, in a device with two gears, if one gear is twice the diameter of the
other, the ratio would be 2:1.
One of the most primitive types of gears we could look at would be a wheel with wooden
pegs sticking out of it.
The problem with this type of gear is that the distance from the center of each gear to the
point of contact changes as the gears rotate. This means that the gear ratio changes as the gear
turns, meaning that the output speed also changes. If you used a gear like this in your car, it
would be impossible to maintain a constant speed you would be accelerating and decelerating
constantly.
Worm gears
These are used when large gear reductions are needed. It is common for worm gears to
have reductions of 20:1, and even up to 300:1 or greater.
Many worm gears have an interesting property that no other gear set has: the worm can
easily turn the gear, but the gear cannot turn the worm. This is because the angle on the worm is

88

so shallow that when the gear tries to spin it, the friction between the gear and the worm holds
the worm in place. The worm gear is shown in the below figure.

Motor and Gear Reduction
It takes a lot of force to accelerate the wiper blades back and forth across the windshield
so quickly. In order to generate this type of force, a worm gear is used on the output of a small
electric motor.
The worm gear reduction can multiply the torque of the motor by about 50 times, while
slowing the output speed of the electric motor by 50 times as well. The output of the gear
reduction operates a linkage that moves the wipers back and forth.
89

Inside the motor/gear assembly is an electronic circuit that senses when the wipers are in
their down position. The circuit maintains power to the wipers until they are parked at the bottom
of the windshield, and then cuts the power to the motor. This circuit also parks the wipers
between wipes when they are on their intermittent setting.
Linkage
A short cam is attached to the output shaft of the gear reduction. This cam spins around
as the wiper motor turns. The cam is connected to a long rod; as the cam spins, it moves the rod
back and forth. The long rod is connected to a short rod that actuates the wiper blade on the
driver's side. Another long rod transmits the force from the driver-side to the passenger-side
wiper blade.
Operational Specifications of Motors are shown in below Table.

Description of the wiper motors selected
The motor is two pole design having high energy permanent magnets, together with a
gear box housing, having two stages of gear reduction .power from the motor is a transferred by
a three start worm on a extension of the armature shaft through a two stage gear system.
A ball bearing system is provided on the commutator end of the armature to minimize the
friction losses and thereby increase torque of the wiper motor. Power from the final gear arm
spindles .A special inbuilt limit switch ensures in applying regenerative braking to the OFF
position.
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Thermal protector is connected in series with armature to avoid burning of armature
under locked position. Consistent parking of the wiper arms and blades in the correct position is
there by ensured. The side on which the arms come to rest is preset to requirements.
Electrical connections are made to the motor via a non-reversible in line plug and socket
assembly .This type of connections ensures that the correct motor polarity is maintained when
the motor is connected to the vehicle wiring. The wiper motor incorporates radio interference
capacitor.

4.9 LIQUID CRYSTAL DISPLAY:
LCD stands for Liquid Crystal Display. LCD is finding wide spread use replacing LEDs (seven
segment LEDs or other multi segment LEDs) because of the following reasons:
1. The declining prices of LCDs.
2. The ability to display numbers, characters and graphics. This is in contrast to LEDs,
which are limited to numbers and a few characters.
3. Incorporation of a refreshing controller into the LCD, thereby relieving the CPU of the
task of refreshing the LCD. In contrast, the LED must be refreshed by the CPU to keep
displaying the data.
4. Ease of programming for characters and graphics.
These components are “specialized” for being used with the microcontrollers, which means
that they cannot be activated by standard IC circuits. They are used for writing different
messages on a miniature LCD.

91

A model described here is for its low price and great possibilities most frequently used in
practice. It is based on the HD44780 microcontroller (Hitachi) and can display messages in two
lines with 16 characters each. It displays all the alphabets, Greek letters, punctuation marks,
mathematical symbols etc. In addition, it is possible to display symbols that user makes up on its
own.
Automatic shifting message on display (shift left and right), appearance of the pointer, backlight
etc. are considered as useful characteristics.
Pins Functions

There are pins along one side of the small printed board used for connection to the
microcontroller. There are total of 14 pins marked with numbers (16 in case the background light
is built in). Their function is described in the table below:

Function

Pin Number

Name

Logic State

Description

Ground

1

Vss

-

0V

Power supply

2

Vdd

-

+5V

Contrast

3

Vee

-

0 – Vdd

4

RS

0
1

D0 – D7 are interpreted as
commands
D0 – D7 are interpreted as data

5

R/W

0
1

Write data (from controller to LCD)
Read data (from LCD to controller)

Control of
operating

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Access to LCD disabled
0
Normal operating
1
Data/commands are transferred to
From 1 to 0
LCD

6

E

7

D0

0/1

Bit 0 LSB

8

D1

0/1

Bit 1

9

D2

0/1

Bit 2

10

D3

0/1

Bit 3

11

D4

0/1

Bit 4

12

D5

0/1

Bit 5

13

D6

0/1

Bit 6

14

D7

0/1

Bit 7 MSB

Data / commands

LCD screen:

LCD screen consists of two lines with 16 characters each. Each character consists of 5x7 dot
matrix. Contrast on display depends on the power supply voltage and whether messages are
displayed in one or two lines. For that reason, variable voltage 0-Vdd is applied on pin marked as
Vee. Trimmer potentiometer is usually used for that purpose. Some versions of displays have
built in backlight (blue or green diodes). When used during operating, a resistor for current
limitation should be used (like with any LE diode).

93

LCD Basic Commands
All data transferred to LCD through outputs D0-D7 will be interpreted as commands or as data,
which depends on logic state on pin RS:
RS = 1 - Bits D0 - D7 are addresses of characters that should be displayed. Built in processor
addresses built in “map of characters” and displays corresponding symbols. Displaying position
is determined by DDRAM address. This address is either previously defined or the address of
previously transferred character is automatically incremented.
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RS = 0 - Bits D0 - D7 are commands which determine display mode. List of commands which
LCD recognizes are given in the table below:
Command

RS RW D7 D6 D5 D4 D3 D2 D1 D0 Execution Time

Clear display

0

0

0

0

0

0

0

0

0

1

1.64mS

Cursor home

0

0

0

0

0

0

0

0

1

x

1.64mS

Entry mode set

0

0

0

0

0

0

0

1 I/D S

40uS

Display on/off control

0

0

0

0

0

0

1

D

U

B

40uS

Cursor/Display Shift

0

0

0

0

0

1 D/C R/L x

x

40uS

Function set

0

0

0

0

1 DL N

x

40uS

Set CGRAM address

0

0

0

1

Set DDRAM address

0

0

1

DDRAM address

40uS

Read “BUSY” flag (BF)

0

1

BF

DDRAM address

-

Write to CGRAM or DDRAM

1

0

D7 D6 D5 D4 D3 D2 D1 D0

40uS

Read from CGRAM or DDRAM

1

1

D7 D6 D5 D4 D3 D2 D1 D0

40uS

I/D 1 = Increment (by 1)
0 = Decrement (by 1)
S 1 = Display shift on
0 = Display shift off
D 1 = Display on
0 = Display off
U 1 = Cursor on
0 = Cursor off

F

x

CGRAM address

40uS

R/L 1 = Shift right
0 = Shift left
DL 1 = 8-bit interface
0 = 4-bit interface
N 1 = Display in two lines
0 = Display in one line
F 1 = Character format 5x10 dots
0 = Character format 5x7 dots
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B 1 = Cursor blink on

D/C 1 = Display shift

0 = Cursor blink off

0 = Cursor shift

LCD Connection
Depending on how many lines are used for connection to the microcontroller, there are 8-bit and
4-bit LCD modes. The appropriate mode is determined at the beginning of the process in a phase
called “initialization”. In the first case, the data are transferred through outputs D0-D7 as it has
been already explained. In case of 4-bit LED mode, for the sake of saving valuable I/O pins of
the microcontroller, there are only 4 higher bits (D4-D7) used for communication, while other
may be left unconnected.

Consequently, each data is sent to LCD in two steps: four higher bits are sent first (that normally
would be sent through lines D4-D7), four lower bits are sent afterwards. With the help of
initialization, LCD will correctly connect and interpret each data received.

Besides, with regards to the fact that data are rarely read from LCD (data mainly are transferred
from microcontroller to LCD) one more I/O pin may be saved by simple connecting R/W pin to
the Ground. Such saving has its price.
Even though message displaying will be normally performed, it will not be possible to read from
busy flag since it is not possible to read from display.
LCD Initialization
Once the power supply is turned on, LCD is automatically cleared. This process lasts for
approximately 15mS. After that, display is ready to operate. The mode of operating is set by
default. This means that:
1. Display is cleared
2. Mode
DL = 1 Communication through 8-bit interface
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N = 0 Messages are displayed in one line
F = 0 Character font 5 x 8 dots
3. Display/Cursor on/off
D = 0 Display off
U = 0 Cursor off
B = 0 Cursor blink off
4. Character entry
ID = 1 Addresses on display are automatically incremented by 1
S = 0 Display shift off
Automatic reset is mainly performed without any problems. Mainly but not always! If for any
reason power supply voltage does not reach full value in the course of 10mS, display will start
perform completely unpredictably.

If voltage supply unit can not meet this condition or if it is needed to provide completely safe
operating, the process of initialization by which a new reset enabling display to operate normally
must be applied.

Algorithm according to the initialization is being performed depends on whether connection to
the microcontroller is through 4- or 8-bit interface. All left over to be done after that is to give
basic commands and of course- to display messages.

97

Fig: Procedure on 8-bit initialization.
Contrast control:
To have a clear view of the characters on the LCD, contrast should be adjusted. To adjust the
contrast, the voltage should be varied. For this, a preset is used which can behave like a variable
voltage device. As the voltage of this preset is varied, the contrast of the LCD can be adjusted.

98

Fig: Variable resistor
Potentiometer
Variable resistors used as potentiometers have all three terminals connected. This arrangement is
normally used to vary voltage, for example to set the switching point of a circuit with a sensor, or
control the volume (loudness) in an amplifier circuit. If the terminals at the ends of the track are
connected across the power supply, then the wiper terminal will provide a voltage which can be varied
from zero up to the maximum of the supply.

Potentiometer Symbol

Presets
These are miniature versions of the standard variable resistor. They are designed to be mounted directly
onto the circuit board and adjusted only when the circuit is built. For example, to set the frequency of
an alarm tone or the sensitivity of a light-sensitive circuit, a small screwdriver or similar tool is required
to adjust presets.

99

Presets are much cheaper than standard variable resistors so they are sometimes used in projects where
a standard variable resistor would normally be used.

Multiturn presets are used where very precise adjustments must be made. The screw must be
turned many times (10+) to move the slider from one end of the track to the other, giving very
fine control.

Preset Symbol

LCD Interfacing with 8051:

100

4.10 COM PONENTS DETAILS
Resistor
Resistor is a component that resists the flow of direct or alternating electric
circuit. Resistors can limit or divide the current, reduce the voltage, protect an electric
circuit, or provide large amounts of heat or light. An electric current is the movement of
charged particles called electrons from one region to another. Resistors are usually placed
in electric circuits.
Physicists explain the flow of current through a material, such as a resistor, by
comparing it to water flowing through a pipe. Resistors are designed to have a specific
value of resistance. Resistors used in electric circuits are cylindrical. They are often color
coded by three or four color bands that indicate the specific value of resistance. Resistors
obey ohm‟s law, which states that the current density is directly proportional to the
electric field when the temperature is constant.

Capacitor
Capacitor or electric condenser is a device for storing an electric charge. The
simplest form of capacitor consists of two metal plates separated by a non touching layer
called the dielectric. When one plate is charged with electricity from a direct current or
electrostatic source, the other plate have induced in it a charge of the opposite sign; that
is, positive if the original charge is negative and negative if the original charge is
positive. The electrical size of the capacitor is its capacitance. Capacitors are limited in
the amount of electric charge they can absorb; they can conduct direct current for only
instances but function well as conductors in alternating current circuits. Fixed capacity
and variable capacity capacitors are used in conjunction with coils as resonant circuits in
radios and other electronic equipment. Capacitors are produced in a wide variety of
101

forms. Air, Mica, Ceramics, Paper, Oil, and Vacuums are used as dielectrics depending
on the purpose for which the device is intended.
Transistor
Transistor is a device which transforms current flow from low resistance path to
high resistance path. It is capable of performing many functions of the vacuum tube in
electronic circuits, the transistor is the solid state device consisting of a tiny piece of semi
conducting material, usually germanium or silicon, to which three or more electrical
connections are made.
N-type and P-type Transistor.
A germanium or silicon crystal, containing donor impurity atoms is called a
negative or n-type semiconductor to indicate the presence of excess negatively charged
electrons. The use of an acceptor impurity produces a positive, or p-type semiconductor
so called because of the presence of positively charged holes.
When an electrical voltage is applied, the n-p junction acts as a rectifier,
permitting current to flow in only one direction. If the p-type region is connected to the
positive terminal of the battery and the n-type to the negative terminal, a large current
flows through the material across the junction.
Diode
Diode is a electronic device that allows the passage of current in only one
direction. The first such devices were vacuum-tube diodes, consisting of an evacuated
glass or steel envelope containing two electrodes – a cathode and an anode. The diodes
commonly used in electronic circuits are semiconductor diodes. There are different
diodes used in electronic circuits such as Junction diode, Zener diode, Photo diodes, and
tunnel diode.

102

Junction diodes consist of junction of two different kinds of semiconductor material.
The Zener diode is a special junction type diode, using silicon, in which the voltage
across the junction is independent of the current through the junction.

5. Projects Schematic diagram

103

5.1 Working procedure:
Engine motor control using GSM is carried out in a very efficient way. The user has to send
predefined messages from his mobile to the controlling unit. The controlling unit consists of a
microcontroller, GSM modem, circuitry to allow the serial communication between the
microcontroller and modem and the motor unit.
Whenever the user sends a predefined message to the controlling unit, the modem receives this
and passes the data to the microcontroller. The microcontroller upon reading this data, starts or
stops the vehicle motor as per the request sent by the user. The system can also send a message
as a confirmation reply to the user mobile.
Since the DC motor requires more current for its functioning, the microcontroller cannot handle
the motor and cannot provide the required current to the motor, a current driver IC L293D is
used as an interface between the microcontroller and the DC motor. Thus, the status of the motor
can be changed within no time using the concepts of GSM.

104

6. Firmware Implementation of the project design
This chapter briefly explains about the firmware implementation of the project. The required
software tools are discussed in section 4.2. Section 4.3 shows the flow diagram of the project
design. Section 4.4 presents the firmware implementation of the project design.

6.1 Software Tools Required
Keil µv3, Proload are the two software tools used to program microcontroller. The
working of each software tool is explained below in detail.
6.2 Programming Microcontroller
A compiler for a high level language helps to reduce production time. To program the
AT89S52 microcontroller the Keil µv3 is used. The programming is done strictly in the
embedded C language. Keil µv3 is a suite of executable, open source software development tools
for the microcontrollers hosted on the Windows platform.

The compilation of the C program converts it into machine language file (.hex). This is
the only language the microcontroller will understand, because it contains the original program
code converted into a hexadecimal format. During this step there are some warnings about
eventual errors in the program. This is shown in Fig 4.1. If there are no errors and warnings then
run the program, the system performs all the required tasks and behaves as expected the software
105

developed. If not, the whole procedure will have to be repeated again. Fig 4.2 shows expected
outputs for given inputs when run compiled program.

One of the difficulties of programming microcontrollers is the limited amount of
resources the programmer has to deal with. In personal computers resources such as RAM and
processing speed are basically limitless when compared to microcontrollers. In contrast, the code
on microcontrollers should be as low on resources as possible.

Keil Compiler:
Keil compiler is software used where the machine language code is written and compiled.
After compilation, the machine source code is converted into hex code which is to be dumped
into the microcontroller for further processing. Keil compiler also supports C language code.

106

Fig 4.1: Compilation of source Code

Fig 4.2: Run the compiled program

Proload:
107

Proload is software which accepts only hex files. Once the machine code is converted
into hex code, that hex code has to be dumped into the microcontroller and this is done by the
Proload. Proload is a programmer which itself contains a microcontroller in it other than the one
which is to be programmed. This microcontroller has a program in it written in such a way that it
accepts the hex file from the Keil compiler and dumps this hex file into the microcontroller
which is to be programmed. As the Proload programmer kit requires power supply to be
operated, this power supply is given from the power supply circuit designed above. It should be
noted that this programmer kit contains a power supply section in the board itself but in order to
switch on that power supply, a source is required. Thus this is accomplished from the power
supply board with an output of 12volts.

Fig 4.3: Atmel AT89C2051 Device programmer
Features


Supports major Atmel 89 series devices



Auto Identify connected hardware and devices



Error checking and verification in-built



Lock of programs in chip supported to prevent program copying



20 and 40 pin ZIF socket on-board



Auto Erase before writing and Auto Verify after writing



Informative status bar and access to latest programmed file



Simple and Easy to use



Works on 57600 speed

Description

108

It is simple to use and low cost, yet powerful flash microcontroller programmer for the
Atmel 89 series. It will Program, Read and Verify Code Data, Write Lock Bits, Erase and Blank
Check. All fuse and lock bits are programmable. This programmer has intelligent onboard
firmware and connects to the serial port. It can be used with any type of computer and requires
no special hardware. All that is needed is a serial communication ports which all computers
have.
All devices have signature bytes that the programmer reads to automatically identify the
chip. No need to select the device type, just plug it in and go! All devices also have a number of
lock bits to provide various levels of software and programming protection. These lock bits are
fully programmable using this programmer. Lock bits are useful to protect the program to be
read back from microcontroller only allowing erase to reprogram the microcontroller. The
programmer connects to a host computer using a standard RS232 serial port. All the
programming 'intelligence' is built into the programmer so you do not need any special hardware
to run it. Programmer comes with window based software for easy programming of the devices.

109

Programming Software
Computer side software called 'Proload V4.1' is executed that accepts the Intel HEX format file
generated from compiler to be sent to target microcontroller. It auto detects the hardware
connected to the serial port. It also auto detects the chip inserted and bytes used. Software is
developed in Delphi 7 and requires no overhead of any external DLL.

110

Fig 4.4: Writing the programs bytes onto the microcontrolle r

111

6.3 Project source code
Main code:
#include<reg51.h>
#include"lcddisplay.h"
#include"UART.h"
#include<string.h>
sbit motor = P1^0;
bit l1,control=0;
unsigned char rec[20];
unsigned char str[5],mobilenum[11],msg[20],numcnt;
unsigned char l,s,n,a,b,i,count,ccount,j,jjj,i=0;
unsigned char idata msg1[60];

void main()
{
l1=0;
motor=0;
lcd_init();
UART_init();
lcdcmd(0x85);
msgdisplay("WELCOME");
delay(300);
lcdcmd(0x01);
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msgdisplay("searching for");
lcdcmd(0xc0);
msgdisplay("GSM modem");
delay(100);
send_to_modem("ate0");

//to avoid echo signals,

enter();
send_to_modem("at"); // TO CHECKING GSM MODEM...
enter();
delay(1000);
send_to_modem("at+cmgd=1"); // TO CHECKING GSM MODEM...
enter();
for(s=0;s<5;s++)

// Here we are waiting for data whitch is sending by GSM modem

{
while(RI==0);

// to checking wether the GSM modem connected to system or
// not.

str[s]=SBUF;
RI=0;
}

lcdcmd(0x01);
msgdisplay("SYSTEM");
lcdcmd(0xc3);
msgdisplay("CONNECTED");

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delay(500);
lcdcmd(0x01);
msgdisplay("AGRI MOTOR CTRL ");
lcdcmd(0xC0);
msgdisplay("USING GSM");
delay(500);

send_to_modem("at+cmgf=1");
enter();

st:
while(RI==1)
{
RI=0;
delay(100);
}

if(control)
{
send_to_modem("at+cmgs=");
ch_send_to_modem('"');
send_to_modem(mobilenum);
ch_send_to_modem('"');
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enter();
}

if(l1)
{
lcdcmd(0x01);
msgdisplay("L1 ON: ");
if(control)
send_to_modem("motor ON ");
}
else
{
lcdcmd(0x01);
msgdisplay("L1 OFF: ");
if(control)
send_to_modem("motor OFF ");
}

if(control)
{
ch_send_to_modem(0x1a);
control=0;
while(RI==0);
115

delay(100);
while(RI==1)
{
a=SBUF;
RI=0;
delay(100);
}
}

while(1)
{

if(RI==1)
{
RI=0;
b=SBUF;
while(RI==0);
b=SBUF;
RI=0;
while(RI==0);
b=SBUF;
RI=0;
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while(RI==0);
b=SBUF;
RI=0;
if(b=='C')
{
while(RI==0);
b=SBUF;
RI=0;
if(b=='M')
{
while(RI==0);
b=SBUF;
RI=0;
}
if(b=='T')
{
while(RI==0);
b=SBUF;
RI=0;
}
if(b=='I')
{
lcdcmd(0x01);
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msgdisplay("NEW message ");
delay(100);
lcdcmd(0x01);
send_to_modem("at+cmgr=1");
enter();
count =0;
do
{
while(RI==0);
msg1[count]=SBUF;
RI=0;
count++;
}while(count < 60);
i=0;
while(i < 30)
{
if(i==15)
lcdcmd(0xC0);
lcddata(msg1[i]);
i++;
}
delay(3000);
lcdcmd(0x01);
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while(i < 60)
{
if(i==45)
lcdcmd(0xC0);
lcddata(msg1[i]);
i++;
}
delay(3000);
send_to_modem("at+cmgd=1");
enter();
/*count = 0;
while(count < 4)
{
while(RI==0);
b=SBUF;
RI=0;
count++;
}
count = 0;
while(count < 10)
{
while(RI==0);
mobilenum[count]=SBUF;
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RI=0;
count++;
}
lcddata(mobilenum[count]);
lcddata(b);
msgdisplay(mobilenum);
do
{
while(RI==0);
b=SBUF;
RI=0;
}while(b == '\r' || b == '\n');
while(RI==0);
b=SBUF;
RI=0;
count=0;
do
{
while(RI==0);
rec[count]=SBUF;
RI=0;
count++;
}while(b == '\r' || b == '\n');
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lcdcmd(0x01);
msgdisplay(rec);
delay(1000); */

/* if(!strcmp(rec,"L1 ON"))
{
motor=1;
l1=1;
control=1;
}
else
if(!strcmp(rec,"L1 OFF"))
{
motor=0;
l1=0;
control=1;
}

else */

goto st;

121

}

}

}

}

}

LCD CODE:
#include<reg51.h>
#define lcd_data P2
#define lcd_cont() ((lcd_en=1),(delay(3)),(lcd_en=0))
sbit lcd_rs = P2^1;
sbit lcd_en = P2^0;
void lcd_init(void);
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void lcdcmd(unsigned char value);
void lcddata(unsigned char value);
void msgdisplay(unsigned char b[]);
void delay(unsigned int value);
void lcd_init(void)
{
lcdcmd(0x02);
lcdcmd(0x02);
lcdcmd(0x02);
lcdcmd(0x28);
lcdcmd(0x28);
lcdcmd(0x28);
lcdcmd(0x0c);
lcdcmd(0x06);
lcdcmd(0x01);
}
void lcdcmd(unsigned char value)

// LCD COMMAND

{
lcd_data=value&(0xf0);
lcd_rs=0;
lcd_cont();
lcd_data=((value<<4)&(0xf0));
lcd_rs=0;
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lcd_cont();

void lcddata(unsigned char value)
{
lcd_data=value&(0xf0);
lcd_rs=1;
lcd_cont();
delay(3);
lcd_data=((value<<4)&(0xf0));
lcd_rs=1;
lcd_cont();
delay(3);
}
void msgdisplay(unsigned char b[])
{
unsigned char s,count=0;
for(s=0;b[s]!='\0';s++)
{
lcddata(b[s]);
}
}

124

void delay(unsigned int value)
{
unsigned int x,y;
for(x=0;x<100;x++)
for(y=0;y<value;y++);
}
SERIAL COMMUNICATION CODE:
#include<reg51.h>
void UART_init();
void send_to_modem(char*);
void enter();
void send(char);
void ch_send_to_modem(char*);
void UART_init()
{
SCON = 0x50;
TMOD = 0x20;
TH1 = 0xFD;
TR1 = 1;
}

void send_to_modem(char *s)
{
125

while(*s != '\0')
{
send(*s);
s++;
}
}
void ch_send_to_modem(char *s)
{
while(*s != '\0')
{
send(*s);
s++;
}
send('\r');
send('\n');
}
void send(char x)
{
SBUF = x;
while(TI == 0);
TI = 0;
}
void enter()
126

{
send('\r');
send('\n');
}

127

7. Results and Discussions
Results
Assemble the circuit on the PCB as shown in Fig 5.1. After assembling the circuit on the
PCB, check it for proper connections before switching on the power supply.

Conclusion
A House Security System by using Artificial Neural Network can be developed successfully by
the above suggested methods. It is known that as the number of hidden neurons increases, the
training time and number of epochs to train the network increases proportionately. This problem
was removed by embedding a local adaptive technique, Resilience BPN, for which the training
time is very short.
We proved that BPN is a better method as compared to cryptography and has been employed in
our problem to recall the relationship of User ID and Password that had been registered, as ANN
acts as a “brain” in itself once trained. Hence, it could be used to replace the verification table
used in the conventional system.
We also witnessed how MATLAB can be effectively used to implement the security system as it
has simpler training, adaptation and simulation methods.

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APPLICATIONS:






AC Motor Control
Water Sprinklers Control
Tank Control
Electronic device control etc…

Future Enhancement:
We can design it such that it will be able to give the status of the device back to us via sms.

Advantages:
• It is very safe and secure to use.
• Fast, effective and flawless service.
• We can control any appliances remotely.
• Highly-reliable and efficient to use.
Disadvantage:
If network busy the delivery of SMS may fail, so it‟s difficult to control the appliances.

11. REFRENCES AND BIBLOGRAPHY
 Muhammad Ali Mazidi , Janice Gillispie Mazidi, Rolin D. Mckinlay.
Second edition, “THE 8051 MICROCONTROLLER AND EMBEDDED SYSTEM”

129

 K. J. Ayala. Third edition, “The 8051 MICROCONTROLLER”
 General information about electronic voting machine
www.eci.gov.in
www.eci.gov.in/faq/evm.asp
www.eci.gov.in/Audio_VideoClips/presentation/EVM.ppt
www.rajasthan.net/election/guide/evm.htm
www.indian-elections.com/electoralsystem/electricvotingmachine.html
 Tutorial on microcontroller:
www.8051projects.net/microcontroller_tutorials/

130