This document appears to be an industrial training report submitted by Jitendra Dhaka to the National Institute of Technology in Hazratbal, Srinagar, India. The report details Dhaka's winter training on embedded systems conducted at TATA CMC Jaipur. It includes an acknowledgements section thanking various individuals and organizations for their support. It also includes a preface describing the benefits of industrial training for engineering students and an overview of the project Dhaka completed - a bidirectional visitor counter and home automation system.

1. NATIONAL INSTITUTE OF
TECHNOLOGY
HAZRATBAL, SRINAGAR
INDUSTRIAL TRAINING & PROJECT REPORT
ON
EMBEDDED SYSTEM
Submitted By - JITENDRA DHAKA
ENROLL- 416/11
7TH
SEM ECE
dhaka.jiten@gmail.com
09086447099

2. ACKNOWLEDGEMENT
I have taken efforts in this training. However, it would not
have been possible without the kind support and help of many
individuals and organizations. I would like to extend my
sincere thanks to all of them. I am highly indebted to TATA
CMC JAIPUR for their guidance and constant supervision as
well as for providing necessary information regarding the
training & also for their support in completing the training. I
would like to express my gratitude towards my parents &
member of TATA CMC JAIPUR for their kind co-operation
and encouragement which help me in completion of this
training. I would like to express my special gratitude and
thanks to industry persons for giving me such attention and
time. My thanks and appreciations also go to my colleague in
developing this training and people who have willingly helped
me out with their abilities.

3. PREFACE
Industrial Training is very important for engineering
students. This training provides them opportunity to be familiar
with the industrial / company environment. During this training
they can show and can enhance their practical skills and gain
practical knowledge and experience for future. This is best way
through which the students can learn the latest technologies
being used in the companies.
I “JITENDRA KUMAR” have undergone through Winter
Training on “Embedded system” from “TATA CMC JAIPUR”.
This training helped me a lot in learning the technologies of
this particular field. I have also done a project on “Bidirectional
Visitor Counter & Home Automation” during the training under
the guidance of “Mr. Vishwesh Kumar Sharma”. During the
Project development I gained practical knowledge of the subject.
Industrial Training & Project work were very challenging but
as I proceeded things got easier. Practical Industrial Training was
an interesting learning experience for me.

4. BIDIRECTIONAL VISITOR COUNTER
& HOME AUTOMATION
CONTENTS
• INTRODUCTION
• PROJECT OVERVIEW
• PCB LAYOUT
• CIRCUIT COMPONENTS
• COMPONENTS DESCRIPTION
• ABOUT MICROCONTROLLER
• POWER SUPPLY
• LCD
• CIRCUIT DESIGN
• OPERATION
• SOFTWARE IN MCU 89S52
• ORIGINAL PCB LAYOUT
• TRANSMITTER & RECEIVER CIRCUIT
• APPLICATION & LIMITATIONS
• PHOTOS OF BIDIRECTIONAL VISITOR COUNTER
AND HOME AUTOMATION
• CONCLUSION

5. INTRODUCTION
The objective of this project is to make a controller
based model to count number of persons visiting particular
room and accordingly light up the room. Here we can use
sensor and can know present number of persons.
In today’s world, there is a continuous need for
automatic appliances with the increase in standard of living,
there is a sense of urgency for developing circuits that would
ease the complexity of life. Also if at all one wants to know
the number of people present in room so as not to have
congestion. This circuit proves to be helpful.

6. PROJECT OVERVIEW
This Project “Bi-directional Visitor Counter and Home
Automation” using Microcontroller is a reliable circuit that
takes over the task of controlling the room lights as well as
counting number of persons/ visitors in the room very
accurately. When somebody enters into the room then the
counter is incremented by one and the light in the room will
be switched ON and when any one leaves the room then the
counter is decremented by one. The light will be only
switched OFF until all the persons in the room go out. The
total number of persons inside the room is also displayed on
the seven segment displays.
The microcontroller does the above job. It receives the
signals from the sensors, and this signal is operated under
the control of software which is stored in ROM.
Microcontroller AT89S52 continuously monitor the
Infrared Receivers, When any object pass through the IR
Receiver’s then the IR Rays falling on the receiver are
obstructed , this obstruction is sensed by the Microcontroller.

7. PCB LAYOUT
BOTTOM SILK PCB LAYOUT

8. TOP SILK PCB LAYOUT

9. CIRCUIT COMPONENTS
Here is the list of components and their corresponding values
used in this circuit.
 5 Resistor of 330 ohms
 2 Variable Resistor of 20 Kohms
 2 Variable Resistor of 50Kohms
 2 Electrolytic Capacitor
 4 Ceramic Capacitor 104
 2 Ceramic Capacitor 33 pF
 11.0592 MHz crystal Oscillator
 AT89S52
 7 segment display
 7805
 7812
 3 LED
 Reset Key
 2 Relay
 ULN2803 Relay Driver IC
 LM324 IC
 IR LED
 IR Phototransistor

10. Components Description:
LED
Light emitting diodes (LEDs) are semiconductor light
sources. The light emitted...
Infrared LED
An IR LED, also known as IR transmitter, is a special purpose
LED that transmits infrared rays in the range of 760 nm
wavelength.
Transistor BC547
BC547 is an NPN bi-polar junction transistor. A transistor,
stands for transfer of resistance, is commonly used to amplify
current. A small current at its base controls a larger current...

11. Seven Segment Display
A seven segment display is the most basic electronic display
device that can display digits from 0-9. They find wide
application in devices that display numeric information like
digital clocks, radio, microwave ovens...
AT89C51 Microcontroller
AT89C51 is an 8-bit microcontroller and belongs to
Atmel's 8051 family. ATMEL 89C51 has 4KB of Flash
programmable and erasable read only memory (...

12. MICROCONTROLLER
Various Type Of Microcontrollers:
 First microcontroller is “8031”
It is Intel’s product. Neither a microprocessor nor a
microcontroller. It is an 8-bit controller. Internally no ROM is
provided i.e. code is outside the chip.
 Second microcontroller is “8051”
It is a first complete 8-bit microcontroller. It is a name of
a family. In which the instruction set, pin configuration,
architecture are same, only memory storage capacity is
different. Internally PROM (programmable read only
memory) is provided so it called one time programmable
(OTP).
 Third microcontroller is “AT89C51”
It is ATMEL’s product. It is a similar to 8051 microcontroller i.e.
having same instruction set, pin configuration, architecture. It is also
8-bit microcontroller. Its cost is only Rs10 more than 8051. It uses
EPROM (erasable programmable read only memory) or FLASH
memory. It is multiple time programmable (MTP) i.e. 1000 times. So
it is better than 8051. In “AT89C51”, C‟ stands for CMOS technology
used in the manufacturing of the I.C.

13. ATMEL89C52
Description:
The AT89C52 is a low-power, high performance CMOS
8-it microcomputer with 8K bytes of Flash programmable and
erasable read only memory (PEROM).
The device is manufactured using Atmel’s high-density
non-volatile memory technology and is compatible with the
industry-standard 80C51 and 80C52 instruction set and
pinout.
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 AT89C52 is a
powerful microcomputer which provides a highly-flexible
and cost-effective solution to many embedded control
applications.

14. The ATMEL89C52 have a total of 40 pins that are
dedicated for various functions such as I/O, RD, WR,
address and interrupts. Out of 40 pins, a total of 32 pins are
set aside for the four ports P0, P1, P2, and P3, where each
port takes 8 pins. The rest of the pins are designated as VCC,
GND, XTAL1, XTAL, RST, EA, and PSEN. All these pins
except PSEN and ALE are used by all members of the 8051

15. Vcc: - Pin 40 provides supply voltage to the chip. The voltage
source is +5 V.
 GND: - Pin 20 is the ground.
 XTAL1 and XTAL2: - The 8051 have an on-chip oscillator
but requires external clock to run it. Most often a quartz
crystal oscillator is connected to input XTAL1 (pin 19) and
XTAL2 (pin 18). The quartz crystal oscillator connected to
XTAL1 and XTAL2 also needs two capacitors of 30 pF
value. One side of each capacitor is connected to the
ground.
 RST:- Pin 9 is the reset pin. It is an input and is active high
(normally low). Upon applying a high pulse to this pin, the
microcontroller will reset and terminate all activities. This is

16. often referred to as a power –on reset. Activating a power-
on reset will cause all values in the registers to be lost.
Circuit Connection of Reset Pin
 PSEN:- This is an output pin. PSEN stands for “program
store enable.” It is the read strobe to external program
memory. When the microcontroller is executing from
external memory, PSEN is activated twice each machine
cycle.
 ALE:- ALE (Address latch enable) is an output pin and is
active high. When connecting a microcontroller to external
memory, potr 0 provides both address and data. In other
words the microcontroller multiplexes address and data
through port 0 to save pins. The ALE pin is used for de-
multiplexing the address and data by connecting to the G
pin of the 74LS373 chip.

17.  I/O port pins and their functions:- The four ports P0, P1,
P2, and P3 each use 8 pins, making them 8-bit ports. All
the ports upon RESET are configured as output, ready to
be used as output ports. To use any of these as input port,
it must be programmed.
 Port 0:- Port 0 occupies a total of 8 pins (pins 32 to 39). It
can be used for input or output. To use the pins of port 0 as
both input and output ports, each pin must be connected
externally to a 10K-ohm pull-up resistor. This is due to fact
that port 0 is an open drain, unlike P1, P2 and P3. With
external pull-up resistors connected upon reset, port 0 is
configured as output port. In order to make port 0 an input,
the port must be programmed by writing 1 to all the bits of
it. Port 0 is also designated as AD0-AD7, allowing it to be
used for both data and address. When connecting a
microcontroller to an external memory, port 0 provides both
address and data. The microcontroller multiplexes address
and data through port 0 to save pins. ALE indicates if P0
has address or data. When ALE=0, it provides data D0-D7,
but when ALE=1 it has address A0-A7. Therefore, ALE is
used for de-multiplexing address and data with the help of
latch 74LS373.

18.  Port 1:- Port 1 occupies a total of 8 pins (pins 1 to 8). It can
be used as input or output. In contrast to port 0, this port
does not require pull-up resistors since it has already pull-
up resistors internally. Upon reset, port 1 is configures as
an output port. Similar to port 0, port 1 can be used as an
input port by writing 1 to all its bits.
 Port 2:- Port 2 occupies a total of 8 pins (pins 21 to 28). It
can be used as input or output. Just like P1, port 2 does not
need any pull-up resistors since it has pull-up resistors
internally. Upon reset port 2 is configured as output port. To
make port 2 input, it must be programmed as such by
writing 1s to it.
 Port 3:- Port 3 occupies a total of 8 pins (pins 10 to 17). It
can be used as input or output. P3 does not need any pull-
up resistors, the same as P1 and P2 did not. Although port
3 is configured as output port upon reset, this is not the way
it is most commonly used. Port 3 has an additional function
of providing some extremely important signals such as
interrupts. Some of the alternate functions of P3 are listed
below:
P3.0 RXD (Serial input)
P3.1 TXD (Serial output)
P3.2 INT0 (External interrupt 0)

19. P3.3 INT1 (External interrupt 1)
P3.4 T0 (Timer 0 external input)
P3.5 T1 (Timer 1 external input)
P3.6 WR (External memory write strobe)
P3.7 RD (External memory read strobe)
MEMORY SPACE ALLOCATION:-
The 8051 has three very general types of memory. To
effectively program the 8051 it is necessary to have a basic
understanding of these memory types. The memory types
are illustrated in the following graphic. They are: On-Chip
Memory, External Code Memory, and External RAM.
On chip ROM:- The 89C51 has a 4K bytes of on-chip ROM.
This 4K bytes ROM memory has memory addresses of 0000
to 0FFFh. Program addresses higher than 0FFFh, which
exceed the internal ROM capacity will cause the
microcontroller to automatically fetch code bytes from
external memory. Code bytes can also be fetched exclusively
from an external memory, addresses 0000h to FFFFh, by
connecting the external access pin to ground. The program
counter doesn‟t care where the code is: the circuit designer
decides whether the code is found totally in internal ROM,

20. totally in external ROM or in a combination of internal and
external ROM.
On chip RAM:- The 1289 bytes of RAM inside the 8051 are
assigned addresses 00 to 7Fh. These 128 bytes can be
divided into three different groups as follows:
A total of 32 bytes from locations 00 to 1Fh are set aside
for register banks and the stack. A total of 16 bytes from
locations 20h to 2Fh are set aside for bit addressable
read/write memory and instructions.

21. ROM & RAM Memory in The 8051 mc
External Code Memory
External Code Memory is code (or program) memory
that resides off-chip. This is often in the form of an external
EPROM.
External RAM
External RAM is RAM memory that resides off-chip. This
is often in the form of standard static RAM or flash refers to
any memory (Code, RAM, or other) that physically exists on
the microcontroller itself. On-chip memory can be of several
types, but we'll get into that shortly.
Code Memory
Code memory is the memory that holds the actual 8051
prk2ogram that is to be run. This memory is limited to 64K
and comes in many shapes and sizes: Code memory may be
found on-chip, either burned into the microcontroller as ROM
or EPROM. Code may also be stored completely off-chip in
an external ROM or, more commonly, an external EPROM.
Flash RAM is also another popular method of storing a
program. Various combinations of these memory types may
also be used--that is to say, it is possible to have 4K of code
memory on-chip and 64k of code memory offchip in an
EPROM.

22. Registers
In the CPU, registers are used to store information
temporarily. That information could be a byte of data to be
processed, or an address pointing to the data to be fetched.
In the 8051 there is only one data type: 8 bits. With an 8- bit
data type, any data larger than 8 bits has to be broken into
8-bit chunks before it is processed.
The most commonly used registers of the 8051 are A
(accumulator), B, R0, R1, R2, R3, R4, R5, R6, R7, DPTR
(data pointer) and PC (program counter). All the above
registers are 8-bit registers except DPTR and the program
counter. The accumulator A is used for all arithmetic and
logic instructions.
Some 8051 8-bit registers
R7 R6 R5 R4 R3 R2
R1 R0 B A

23. Some 8051 16-bit registers
PC(program counter)
DPL
DPH
DPTR
PC
Program Counter and Data Pointer
The program counter is a 16- bit register and it points to
the address of the next instruction to be executed. As the
CPU fetches op-code from the program ROM, the program
counter is incremented to point to the next instruction. Since
the PC is 16 bit wide, it can access program addresses 0000
to FFFFH, a total of 64K bytes of code. However, not all the
members of the 8051 have the entire 64K bytes of on-chip
ROM installed.
Flag bits and the PSW Register
Like any other microprocessor, the 8051 have a flag
register to indicate arithmetic conditions such as the carry bit.
The flag register in the 8051 is called the program status
word (PSW) register.
The program status word (PSW) register is an 8-bit
register. It is also referred as the flag register. Although the
PSW register is 8-bit wide, only 6 bits of it are used by the

24. microcontroller. The two unused bits are user definable flags.
Four of the flags are conditional flags, meaning they indicate
some conditions that resulted after an instruction was
executed. These four are CY (carry), AC (auxiliary carry), P
(parity), and OV (overflow). The bits of the PSW register are
shown below:
CY PSW.7 Carry flag
AC PSW.6 Auxiliary carry flag
PSW.5 Available to the user for general purpose
RS1 PSW.6 Register bank selector bit 1
RS0 PSW.3 Register bank selector bit 0
OV PSW.2 Overflow flag
F0 PSW.1 User definable bit
P PSW.0 Parity flag
CY, the carry flag
This flag is set whenever there is a carry out from the d7
bit. This flag bit is affected after an 8-bit addition or
subtraction. It can also be set to 1 or 0 directly by an
instruction such as “SETB C” and “CLR C” where “SETB C”
stands for set bit carry and “CLR C” for clear carry.

25. AC, the auxiliary carry flag
If there is carry from D3 to D4 during an ADD or SUB
operation, this bit is set: otherwise cleared. This flag is used
by instructions that perform BCD arithmetic.
P, the parity flag
The parity flag reflects the number of 1s in the accumulator
register only. If the register A contains an odd number of 1s,
then P=1.Therefore, P=0 if A has an even number of 1s.
OV, the overflow flag
This flag is set whenever the result of a signed number
operation is too large, causing the high order bit to overflow
into the sign bit. In general the carry flags is used to detect
errors in unsigned arithmetic operations
POWER SUPPLY UNIT (+5V)
Power supplies are designed to convert high voltage AC
mains electricity to a suitable low voltage supply for
electronic circuits and other devices. A power supply can by
broken down into a series of blocks, each of which performs
a particular function.

26. Each of the block has its own function as described below
Transformer – steps down high voltage AC mains to low
voltage AC.
Rectifier – converts AC to DC, but the DC output is
varying.
Smoothing – smooths the DC from varying greatly to a
small ripple.
Regulator – eliminates ripple by setting DC output to a
fixed voltage.

27. LIQUID CRYSTAL DISPLAYS (LCD)
Liquid crystal displays (LCD) are widely used in recent
years as compares to LEDs. This is due to the declining
prices of LCD, the ability to display numbers, characters and
graphics, incorporation of a refreshing controller into the
LCD, their by relieving the CPU of the task of refreshing the
LCD and also the ease of programming for characters and
graphics. HD 44780 based LCDs are most commonly used.
LCD pin description:
The LCD discuss in this section has the most common
connector used for the Hitachi 44780 based LCD is 14 pins
in a row and modes of operation and how to program and
interface with microcontroller is describes in this section.

28. VCC,VSS,VEE:
The voltage VCC and VSS provided by +5V and ground
respectively while VEE is used for controlling LCD contrast.
Variable voltage between Ground and Vcc is used to specify
the contrast (or "darkness") of the characters on the LCD
screen.
RS (register select):
There are two important registers inside the LCD. The RS
pin is used for their selection as follows. If RS=0, the
instruction command code register is selected, then allowing
to user to send a command such as clear display, cursor at
home etc.. If RS=1, the data register is selected, allowing the
user to send data to be displayed on the LCD.
R/W (read/write):
The R/W (read/write) input allowing the user to write
information from it. R/W=1, when it read and R/W=0, when it
writing.
EN (enable):
The enable pin is used by the LCD to latch information
presented to its data pins. When data is supplied to data pins,

29. a high power, a high-to-low pulse must be applied to this pin
in order to for the LCD to latch in the data presented at the
data pins.
D0-D7 (data lines):
The 8-bit data pins, D0-D7, are used to send information
to the LCD or read the contents of the LCD‟s internal
registers. To displays the letters and numbers, we send
ASCII codes for the letters A-Z, a-z, and numbers 0-9 to
these pins while making RS =1. There are also command
codes that can be sent to clear the display or force the cursor
to the home position or blink the cursor.
We also use RS =0 to check the busy flag bit to see if the
LCD is ready to receive the information. The busy flag is D7
and can be read when R/W =1 and RS =0, as follows: if R/W
=1 and RS =0, when D7 =1(busy flag =1), the LCD is busy
taking care of internal operations and will not accept any
information. When D7 =0, the LCD is ready to receive new
information.

30. INTERFACING OF LCD WITH MICROCONTROLLER:
An intelligent LCD has two lines with 20 characters each
line. The display contains two internal byte wide registers,
one for commands and second for characters to be
displayed. It also contains a user programmed RAM area that
can be programmed to generate any desired character that
can be formed using a dot matrix. To distinguish between
these two data areas, the hex command byte 80 will be used
to signify that the display RAM address 00h is chosen.
From diagram Port 1 of microcontroller is used for 8 bit
data display on the LCD. Data lines of the LCD Pin no.7 to
pin no 14 are connected to the port 1 of the microcontroller.
The control pin no.4 register select is connected to P3.5, pin
no.5 of
LCD for Read/write is connected to P3.6 and the enable
pin (6) is connected to microcontroller

32. Circuit Design
The heart of the circuit design lies in designing the
microcontroller interface. Here we use the microcontroller
AT89S52. The microcontroller AT89S52 is interfaced to the
IR sensor pairs at two ports pins – P1.0 and P1.1
respectively. The 7 segment display is interfaced to the
microcontroller at port P2.
Another important aspect of the design involves designing the
oscillator circuit and the reset circuit. The oscillator circuit is
designed by selecting an 11.0592MHz quartz crystal and two
ceramic capacitors each 33pF.
The reset circuit is designed by selecting an electrolyte
capacitor of 10uF to ensure a reset pulse width of 100ms and
reset pin voltage drop of 1.2V.
The sensor circuit is designed by selecting appropriate
value of resistors for both the LED and the phototransistor.

33. Operation:
When the system is powered, the compiler initially
initializes the stack pointer and all other variables. It then
scans the input ports (PortP1.0 first). In the meantime, when
there is no interruption between the IR LED and the
phototransistor of the first sensor pair, the output of the
phototransistor is always at low voltage. In other words port
P1.0 is at logic low level. Now when a transition takes place,
i.e. a logic high level is received at port P1.0, the compiler
sees this as an interruption to sense the passage of a person
or an object between the IR LED and the phototransistor. As
per the program, the count value is increased and this value
is displayed on the Counter. Now the compiler starts
scanning the other input pin-P1.1. Similar to the first sensor
pair, for this sensor pair also the phototransistor conducts in
absence of any interruption and P1.1 is at logic low level. In
case of an interruption, the pin P1.1 goes high
and this interruption is perceived by decreasing the value of
cou;8nt.
The program ensures that the scanning of both the port
pins is done at certain delays so as to avoid confusion of
reading. For instance port P1.0 is scanned for two or three
interruptions so as to ensure the count value is above 1 or 2.

34. SOFTWARE
Keil an ARM Company makes C compilers, macro
assemblers, real-time kernels, debuggers, simulators,
integrated environments, evaluation boards, and emulators
for ARM7/ARM9/Cortex-M3, XC16x/C16x/ST10, 251, and
8051 MCU families.
Compilers are programs used to convert a High Level
Language to object code. Desktop compilers produce an
output object code for the underlying microprocessor, but not
for other microprocessors
PROGRAM
#include<reg51.h>
sbit s1=P1^0;sbit s2=P1^1;
sbit HB=P3^0;sbit LB=P3^1;
sbit fan1=P3^7;sbit fan2=P3^6;
A[;810]={0xC0,0xF9,0xA4,0x30,0x19,0x12,0x02,0xF8,0x00,0x10};
void show(int,int);
void main()

35. {int a=0,b=0;
while(1)
{if(a==10)
{b++;a=0;}
if(a==-1)
{b--;a=9;}
if(b==-1 || b==10)
{b=0;a=0;}
while(s1==1 && s2==1)
{show(a,b);
if(a<=1)
{fan1=1;fan2=1;}
if(a==2)
{fan1=0;fan2=1;}
if(a>=3)
{fan1=0;fan2=0;}}
if(s1==0 && s2==1)
{while(s1==0 && s2==1)show(a,b);
while(s1==1 && s2==1)show(a,b);
if(s1==1 && s2==0)

36. {while(s1==1 && s2==0)show(a,b);
a++;}}
if(s1==1 && s2==0)
{while(s1==1&&s2==0)show(a,b);
while(s1==1 && s2==1)show(a,b);
if(s1==0 && s2==1)
{while(s1==0 && s2==1)show(a,b);
a--;}}
}}
void show(int a,int b)
{ unsigned int i;
HB=1;LB=0;P2=A[b]; //1st seg.
for(i=0;i<0x04F;2F;i++); //delay
HB=0;LB=1;P2=A[a]; //2nd seg.
for(i=0;i<0x04FF;i++); //delay
}

37. Transmitter &Receiver Circuit

38. Original PCB Layout for Circuit

39. FINAL CIRCUIT

40. Applications:
1. This circuit can be used domestically to get an indication
of number of persons entering a party
2. It can be used at official meetings.
3. It can be used at homes and other places to keep a
check on the number of persons entering a secured
place.
4. It can also be used as home automation system to
ensure energy saving by switching on the loads and
fans only when needed.
Limitations:
1. It is a theoretical circuit and may require few changes in
practical implementation.
2. It is a low range circuit and cannot be implemented at
large areas.
3. With frequent change in the count value, after a certain
time the output may look confusing.

41. Picture of functional Bidirectional
Visitor Counter

44. CONCLUSION
The training was really very good. I have learned on
how to emphasise on important thing which we miss in
our daily life. We keep on learning complex thing while
ignoring basics butimportantaspect that’swhy we don’t
understand everything in good way. From CMC
Academy and especially Mr. Vishwesh Sir I have
learnt thebasics which I hopewill be very beneficial for
me in coming future. Once again I thank everybody of
CMC Family for such a good training program.

45. BIBILOGRAPHY
 home-automation.org/
 “The 8051 Microcontroller and Embedded systems” by Muhammad Ali
Mazidi and Janice Gillispie Mazidi , Pearson Education.
 smart-home-automation-guide.com
 www.atmel.com/atmel/acrobat/doc0265.pdf
 ATMEL 89S51 Data Sheets.
 www.atmel.com