a brief introduction to 8051 microcontroller

8/12/2019 A BRIEF INTRODUCTION TO 8051 MICROCONTROLLER

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A BRIEF INTRODUCTION TO8051 MICROCONTROLLER

When we have to learn about a new computer we have to familiarize about the machine capability we are

using, and we can do it by studying the internal hardware design (devices architecture), and also to know

about the size, number and the size of the registers.A microcontroller is a single chip that contains the

processor (the CPU), non-volatile memory for the program (ROM or flash), volatile memory for input

and output (RAM), a clock and an I/O control unit. Also called a "computer on a chip," billions of

microcontroller units (MCUs) are embedded each year in a myriad of products from toys to appliances to

automobiles. For example, a single vehicle can use 70 or more microcontrollers. The following picture

describes a general block diagram of microcontroller.89s52: The AT89S52 is a low-power, high-

performance CMOS 8-bit microcontroller with 8K bytes of in-system programmable Flash memory. The

device is manufactured using Atmels high-density non-volatile memory technology and is compatible

with the industry-standard 80C51 instruction set and pin out. The on-chip Flash allows the programmemory to be reprogrammed in-system or by a conventional non volatile memory programmer. By

combining a versatile 8-bit CPU with in-system programmable Flash on a monolithic chip, the Atmel's

AT89S52 is a powerful microcontroller which provides a highly-flexible and cost-effective solution to

many embedded control applications. The AT89S52 provides the following standard features: 8K bytes

of Flash, 256 bytes of RAM, 32 I/O lines, Watchdog timer, two data pointers, three 16-bit

timer/counters, a six-vector two-level interrupt architecture, a full duplex serial port, on-chip oscillator,

and clock circuitry. 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 con-tents but freezes the oscillator, disabling all other chip functions

until the next interrupt. The hardware is driven by a set of program instructions, or software. Once

familiar with hardware and software, the user can then apply the microcontroller to the problems easily.

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

The following are some of the capabilities of 8051 microcontroller.

Internal ROM and RAM

I/O ports with programmable pins

Timers and counters

Serial data communication


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INTRODUCTION

Amicrocontroller is a computer-on-a-chip built for specific tasks such as displaying/receiving information

through LEDs or remote controlled devices. 8051 introduced the world to the most revolutionary set of

microcontrollers.

Apart from 8051, 8052 and 8031 complete the 8051 family. The 8052 microcontroller has 256 bytes of

RAM and 3 timers. Programs written for 8051 projects can be used for 8052 as well. The 8031 has all

features of 8051 except that it is ROM-less. An external ROM that is as large as 64 k bytes can be

programmed and added to this chip for execution. The main disadvantage of adding external ROM is that 2

out of 4 ports are used up leaving less for I/O operations.

The different types of memory used in 8051 are:

i. Internal RAMLocated from address 0 to 0xff.

ii. Special Function Registers (SFR)Located from address 0x80 to 0Xff.

iii. Program MemoryLocated at address 0. Uses 16 bit Special Function Register DPTR, to save the tables

of constants.

iv. External Data MemoryLocated at address 0. Uses MOVX (Move External) to access the external data

memory.

8051s history dates back to when Intel Corporation first built the 8 bit microcontroller in 1981. This

microcontroller was referred as system on a chip because it had 128 bytes of RAM, 4 Kbytes of ROM, 2Timers, 1 Serial port, and four ports on a single chip.

Intel permitted other microcontroller manufacturers to fabricate different versions of 8051 with the condition

that code compatibility should be maintained. The advantage of this is that when the program is written, it

can be used for any version of 8051 irrespective of manufacturer.
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8051 BLOCK DIAGRAM

8051 Microcontroller Block Diagram Explanation:

CPU (Central Processor Unit):

As you may be familiar that Central Processor Unit or CPU is the mind of any processing machine. It

scrutinizes and manages all processes that are carried out in the Microcontroller. User has no power over the

functioning of CPU. It interprets program printed in storage space (ROM) and carries out all of them and do

the projected duty.

Interrupts:

As the heading put forward, Interrupt is a sub-routine call that reads the Microcontrolle rs key function or

job and helps it to perform some other program which is extra important at that point of time. The

characteristic of Interrupt is extremely constructive as it aids in emergency cases. Interrupts provides us a


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method to postpone or delay the current process, carry out a sub-routine task and then all over again restart

standard program implementation.

The Micro-controller 8051 can be assembled in such a manner that it momentarily stops or break the core

program at the happening of interrupt. When sub-routine task is finished then the implementation of core

program initiates automatically as usual. There are 5 interrupt supplies in 8051 Microcontroller, two out offive are peripheral interrupts, two are timer interrupts and one is serial port interrupt.

Memory:

Micro-controller needs a program which is a set of commands. This program enlightens Microcontroller to

perform precise tasks. These programs need a storage space on which they can be accumulated and interpret

by Microcontroller to act upon any specific process. The memory which is brought into play to accumulate

the program of Microcontroller is recognized as Program memory or code memory. In common language

its also known as Read Only Memory or ROM.

Micro-controller also needs a memory to amass data or operands for the short term. The storage space which

is employed to momentarily data storage for functioning is acknowledged as Data Memory and we employ

Random Access Memory or RAM for this principle reason. Microcontroller 8051 contains code memory or

program memory 4K so that is has 4KB Rom and it also comprise of data memory (RAM) of 128 bytes.

Bus:

Fundamentally Bus is a group of wires which functions as a communication canal or mean for the transfer

Data. These buses comprise of 8, 16 or more cables. As a result, a bus can bear 8 bits, 16 bits all together.

There are two types of buses:

1. Address Bus:Microcontroller 8051 consists of 16 bit address bus. It is brought into play to address

memory positions. It is also utilized to transmit the address from Central Processing Unit to Memory.

2. Data Bus:Microcontroller 8051 comprise of 8 bits data bus. It is employed to cart data.

Oscillator:

As we all make out that Microcontroller is a digital circuit piece of equipment, thus it needs timer for its

function. For this function, Microcontroller 8051 consists of an on-chip oscillator which toils as a time

source for CPU (Central Processing Unit). As the productivity thumps of oscillator are steady as a result, it

facilitates harmonized employment of all pieces of 8051 Microcontroller. Input/output Port: As we are

acquainted with that Microcontroller is employed in embedded systems to manage the functions of devices.

Thus to gather it to other machinery, gadgets or peripherals we need I/O (input/output) interfacing ports in

Micro-controller. For this function Micro-controller 8051 consists of 4 input/output ports to unite it to other

peripherals.

Timers/Counters: Micro-controller 8051 is incorporated with two 16 bit counters & timers. The counters are

separated into 8 bit registers. The timers are utilized for measuring the intervals, to find out pulse width etc.


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8051 Architecture

16 bit PC &data pointer (DPTR)

8 bit program status word (PSW)

8 bit stack pointer (SP)

Internal ROM 4k

Internal RAM of 128 bytes.

4 register banks, each containing 8 registers

80 bits of general purpose data memory

32 input/output pins arranged as four 8 bit ports P0-P3

Two 16 bit timer/counters: T0-T1

Two external and three internal interrupt sources

Oscillator and clock circuits

For any electronics project the power supply plays a very important role in its proper functioning. In this

project we are using external A.C supply (220 v) as input, this high voltage is converted into 12 Volts A.C

by step down transformer, then we use voltage regulators and filters with bridge rectifier to convert the A.C

into D.C voltage. For voltage regulation we are using LM 7805 and 7812 to produce ripple free 5 and 12

Volts D.C constant supply.

A circuit breaker capable of microcontroller-based fault detection having a backup circuit for causing the

circuit to trip in response to a microcontroller fault or a failure of a regulated power supply powering the

microcontroller. The circuit breaker includes an RC circuit connected to an SCR. The resistor of the RC

circuit is connected between the anode and gate of the SCR, and the capacitor is connected between the gateand cathode of the SCR. The microcontroller has a first pin coupled to the RC circuit, which is initially in a

high input impedance state. In the event of a microcontroller fault or power supply failure, the capacitor will


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charge to a voltage sufficient to activate the SCR and trip the breaker. If the microcontroller start-up routine

is successful, the pin is configured as an output and is pulled low, shorting out the capacitor.

DESCRIPTION OF 8051INTERFACINGS

It is very important to keep a track of the working of almost all the automated and semi-automated devices,

be it a washing machine, an autonomous robot or anything else. This is achieved by displaying their status

on a small display module.LCD (Liquid Crystal Display) screen is such a display module and a 16x2 LCD

module is very commonly used. These modules are replacingseven segments and other multi segment LEDs

for these purposes. The reasons being: LCDs are economical, easily programmable, have no limitation of

displaying special & evencustom characters (unlike in seven segments), animations and so on. LCD can be

easily interfaced with a microcontroller to display a message or status of a device. This topic explains the

basics of a 16x2 LCD and how it can be interfaced withAT89C51 to display a character.
http://engineersgarage.com/content/lcdhttp://engineersgarage.com/content/seven-segment-displayhttp://engineersgarage.com/content/how-create-custom-characters-16x2-lcd-using-at89c51http://engineersgarage.com/content/microcontroller-at89c51http://engineersgarage.com/content/microcontroller-at89c51http://engineersgarage.com/content/how-create-custom-characters-16x2-lcd-using-at89c51http://engineersgarage.com/content/seven-segment-displayhttp://engineersgarage.com/content/lcd


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controlling display etc. The data register stores the data to be displayed on the LCD. The data is the ASCII

value of the character to be displayed on the LCD. Click to learn more about internal structure of aLCD.

PinDiagram:
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Pin Description:

Pin No Function Name

1 Ground (0V) Ground

2 Supply voltage; 5V (4.7V5.3V) Vcc

3 Contrast adjustment; through a variable resistor VEE

4 Selects command register when low; and data register when high Register Select

5 Low to write to the register; High to read from the register Read/write

6 Sends data to data pins when a high to low pulse is given Enable

7

8-bit data pins

DB0

8 DB1

9 DB2

10 DB3

11 DB4

12 DB5

13 DB6

14 DB7

15 Backlight VCC(5V) Led+

16 Backlight Ground (0V) Led-

SEVEN SEGMENT


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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, electronic meters etc. The most common configuration has an array of eight LEDs arranged in a

special pattern to display these digits. They are laid out as a squared-off figure 8.Every LED is assigned a

name from 'a' to 'h' and is identified by its name. Seven LEDs 'a' to 'g' are used to display the numerals while

eighth LED 'h' is used to display the dot/decimal.

A seven segment is generally available in ten pin package. While eight pins correspond to the eight LEDs,

the remaining two pins (at middle) are common and internally shorted. These segments come in two

configurations, namely, Common cathode (CC) and Common anode (CA). In CC configuration, the negative

terminals of all LEDs are connected to the common pins. The common is connected to ground and a
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particular LED glows when its corresponding pin is given high. In CA arrangement, the common pin is

given a high logic and the LED pins are given low to display a number

AT89C51 MICROCONTROLLER

AT89C51 is an 8-bitmicrocontroller and belongs to Atmel's8051 family.ATMEL 89C51has 4KB of Flash

programmable and erasable read only memory (PEROM) and 128 bytes of RAM. It can be erased and

program to a maximum of 1000 times.

In 40 pin AT89C51, there are four ports designated as P1, P2, P3and P0. All these ports are 8-bit bi-

directional ports, i.e., they can be used as both input and output ports. Except P0which needs external pull-

ups, rest of the ports have internal pull-ups. When 1s are written to these port pins, they are pulled high by

the internal pull-ups and can be used as inputs. These ports are also bit addressable and so their bits can also

be accessed individually.
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Port P0and P2are also used to provide low byte and high byte addresses, respectively, when connected to an

external memory. Port 3 has multiplexed pins for special functions likeserial communication, hardware

interrupts, timer inputs and read/write operation from external memory. AT89C51 has an inbuilt UART for

serial communication. It can be programmed to operate at different baud rates. Including twotimers &

hardwareinterrupts,it has a total of six interrupts.

Pin Diagram:
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Pin Description:

Pin

No

Function Name

1

8 bit input/output port (P1) pins

P1.0

2 P1.1

3 P1.2

4 P1.3

5 P1.4

6 P1.5

7 P1.6

8 P1.7

9 Reset pin; Active high Reset

10Input (receiver) for serial

communicationRxD

8 bit

input/output

port (P3) pins

P3.0

11Output (transmitter) for serial

communicationTxD P3.1

12 External interrupt 1 Int0 P3.2

13 External interrupt 2 Int1 P3.3

14 Timer1 external input T0 P3.4

15 Timer2 external input T1 P3.5

16 Write to external data memory Write P3.6


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17 Read from external data memory Read P3.7

18

Quartz crystal oscillator (up to 24 MHz)

Crystal 2

19 Crystal 1

20 Ground (0V) Ground

21


/

High-order address bits when interfacing with external memory

P2.0/ A8

22 P2.1/ A9

23 P2.2/ A10

24 P2.3/ A11

25 P2.4/ A12

26 P2.5/ A13

27 P2.6/ A14

28 P2.7/ A15

29 Program store enable; Read from external program memory PSEN

30

Address Latch Enable ALE

Program pulse input during Flash programming Prog

31

External Access Enable; Vcc for internal program executions EA

Programming enable voltage; 12V (during Flash programming) Vpp

32


Low-order address bits when interfacing with external memory

P0.7/ AD7

33 P0.6/ AD6

34 P0.5/ AD5

35 P0.4/ AD4

36 P0.3/ AD3

37 P0.2/ AD2


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CODE LOGIC

To create a particular effect, any of these code(s) can be used in a pattern. For example, shifting the entire

display right (5H) in a loop will keep moving the text to right. To create oscillating text, first keep shifting

the string to right (for say, 8 positions) and then shift it to left. This left-right shifting can be done in an

infinite loop.

Hex Code Command to LCD Instruction Register

1 Clear screen display

2 Return home

4 Decrement cursor

6 Increment cursor

5 Shift display right

7 Shift display left

8 Display OFF, cursor OFF

A Display OFF, cursor ON

C Display ON, cursor OFF

E Display ON, cursor blinking

10 Shift cursor position to left

14 Shift cursor position to right

18 Shift the entire display to the left

1C Shift the entire display to the right80 Force the cursor to the beginning of the 1stline

C0 Force cursor to the beginning of the 2n line

38 Use 2 lines and 5x7 matrix


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Here P2is used as output port of the 8051 microcontroller (AT89C51) which sends the data byte to data pins

of the LCD. The control pins (pin 4, 5 & 6) are connected to pins 0, 1 & 6, respectively, of P 3port of the

microcontroller. Pin 3 is connected to apreset of 10k to adjust the contrast on LCD screen.

CODE (ASSEMBLE PROGRAMME OR C PROGRAMME)

// Program to display dynamic text on LCD

#include

#define msec 50

sbit rs=P3^0; //Register select (RS)

sbit rw=P3^1; //Read write (RW) pin

sbit en=P3^6; //Enable (EN) pin

unsigned char commands[]={0x38,0x0E,0x01,0x06,'\0'}; //Command to be sent to LCD

char name[]={"ECE Rocks"}; //String to be displayed on LCD

void delay(unsigned int time) //Time delay function

{

unsigned int i,j;

for(i=0;i


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}

void lcdcmd(unsigned char value) //Function for sending values to the command register of LCD

{

P2=value;

rs=0;

rw=0;

en=1;

delay(1);

en=0;

return;

}

void display(unsigned char value) //Function for sending values to the data register of LCD

{

P2=value;

rs=1;

rw=0;

en=1;

delay(1);

en=0;

return;

}


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void main()

{

int i,j;

for(i=0;commands[i]!='\0';i++) //Sending string to LCD

{

lcdcmd(commands[i]);

delay(msec);

}

for(j=0;name[j]!='\0';j++)

{

display(name[j]);

delay(msec);

}

while(1)

{

lcdcmd(0x1C); //Shift the entire display to right

delay(75);

}

}


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PROTEUS DESIGNED CIRCUIT DIAGRAM


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RESULT (SCREEN SHOTS OF RUNNING PROJECT)


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CONCLUSION

The project was easy to make. The designing and coding of the project was not also much difficult.

However, the components are not readily available in electronics market. The LCD was run short in market

and finally found from old stock of a shop. Most of the microcontrollers available in market are out of order

and there is no replace offered by shop keeper of it. Therefore, we wasted our money for

4microcontrollers and finally the fifth one we purchase was a good microcontroller.

One thing that we got from our experience is that simulation made on proteus is not accurate. When we

simulated the circuit on proteus, the time delay observed was approx. 8 sec. However, practically it is 0.5

sec.

Once the microcontroller is programmed, then the Connections on bread board were not difficult to make.

However initially the LCD didntshow any display. We checked all the components. The components were

in perfect order. After much thought we changed the value of resistance on rheostat which changed the

brightness of LCD. Hence finally the string is displayed and then it moved dynamically to left. In nut

shell, the project is accomplished after a little difficulty in the end and the HEX file is executed well such

that the cursor appears on LCD screen, the cursor increments further such that the string Welcome to

RCETappears. After the string appeared, it moves to left. After a delay of 0.5 sec., the string blinks again

and then move to right and then there comes another delay. This routine continues for an infinite span oftime unless the power supplied to the circuit is disconnected.

APPLICATIONS:

The project have many applications we may see in our daily life. Some of them are as follows:

The ticket booth LCD counters of banks.

Advertisement boards.

News displaying LCD boards installed on traffic signals.

Digital Clocks.

Flight timing displaying boardson airports.
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REFERENCE

http://www.engineersgarage.com

en.wikipedia.org

http://vediktronics.blogspot.in

http://vj86.hubpages.com

http://www.slideshare.net

http://www.slideshare.net

The 8051 Microcontroller And Embedded Systems Using Assembly And C, 2/E by mazidi
http://www.engineersgarage.com/http://www.engineersgarage.com/http://vediktronics.blogspot.in/http://vediktronics.blogspot.in/http://vj86.hubpages.com/http://vj86.hubpages.com/http://www.slideshare.net/http://www.slideshare.net/http://www.slideshare.net/http://www.slideshare.net/http://www.slideshare.net/http://www.slideshare.net/http://vj86.hubpages.com/http://vediktronics.blogspot.in/http://www.engineersgarage.com/

a brief introduction to 8051 microcontroller

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