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Introduction to 8051 Microcontroller

Introduction –

8051 is one of the first and most popular microcontrollers also known as MCS-51. Intel introduced it in the year 1981. Initially, it came out as an N-type metal-oxide-semiconductor (NMOS) based microcontroller, but later versions were based on complementary metal-oxide-semiconductor(CMOS) technology. These microcontrollers were named 80C51, where C in the name tells that it is based on CMOS technology. It is an 8-bit microcontroller which means the data bus is 8-bit. Therefore, it can process 8 bits at a time. It is used in a wide variety of embedded systems like robotics, remote controls, the automotive industry, telecom applications, power tools, etc. 

It is referred to as a System on a Chip (SoC) microcontroller because it is a chip circuit/integrated circuit that holds many components of a computer together on a single chip. These components include a CPU, memory, input-output ports(I/O ports), timers, and secondary storage. Features – There are some key features of 8051 that work as a foundation for students to learn microcontrollers. 

8051 μc family member –

8051 μc have some family members 8052 microcontroller & 8031 microcontroller. 8052μc has 8K bytes of on-chip program ROM instead of 4K bytes, and 128 bytes of RAM. and 8031μc has 0K bytes of on-chip program ROM, and 128 bytes of RAM.

The Key features of the 8051 Microcontroller –

Block Diagram of 8051 μc  –

Block-Structure Diagram

Application of 8051 Microcontroller –

Automation: The 8051 microcontroller is widely used in automotive applications. They are widely used in hybrid vehicles to control engine options. In addition, functions such as cruise control and anti-brake mechanism have been further enhanced thanks to the integration of a microcontroller.

Medical Devices: Convenient medical devices such as blood glucose and blood pressure monitors contain microcontrollers that display measurements.

Energy management: Competent measurement systems support energy consumption calculations in home and industrial environments. These measuring systems are prepared by integrating a microcontroller.

Touch Screen: Many microcontroller vendors incorporate touch functionality into their designs. Portable devices such as media players, and gaming devices.  

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8051 Microcontroller Notes and Study Material PDF Free Download

8051 Microcontroller Notes: Microcontrollers, also known as embedded controllers or embedded systems, are essential in the field of electronics. 8051 Microcontrollers are an important part of the Microprocessors and Microcontrollers (MPMC) course and this topic has a lot of scope as an individual subject as well. Students can refer to the Big Data Lecture Notes For CSE as per the latest and updated syllabus from this article.

For electronics, it is important to have great study materials to be able to do well in exams. Understanding this, we have put together 8051 Microcontroller Notes, along with several other useful references. The more study materials we have for our use, the better we understand the topics at hand. To further add to this, the better our understanding of the topics at hand, the better we are able to fare in our exams.

Listed below are the various study materials we have provided for 8051 Microcontroller in the following article.

Introduction to 8051 Microcontroller Notes – Free PDF Download

8051 Microcontroller Reference Books

8051 microcontroller curriculum, list of 8051 microcontroller important questions.

To learn about and to understand 8051 Microcontroller, we need to pay good attention in our electronics classes. It is also important to be taking adequate notes while sitting through classes. However, sometimes it may be that we are not able to do this. Maybe our mind is focused elsewhere or maybe we were just having a hard time understanding the topic at hand. In a situation like this, you need not worry, especially for 8051 Microcontrollers.

You don’t need to worry about 8051 Microcontroller classes and examinations because we have provided a brilliant set of 8051 Microcontroller Notes for you below. See the list of 8051 Microcontroller Notes below and then make use of them to the ebay of your abilities during your exam preparation.

B.Tech 8051 Microcontroller Notes for Free Downloads

Microcontrollers, which are also called embedded systems or embedded controllers, are imperative to devices. They follow the I/O (input/output) relation, where the input for the controller is put in by the user, and the output is produced by the controller. Each microcontroller has a specific function in a machine which it carries out through the I/O feature. Microcontrollers also consist of a processor and memory, to add to the I/O function.

The 8051 Microcontroller was designed in the year 1981 by the company Intel and is also called the Intel MCS-51. It has several pragmatic and good features, which are listed as follows:

The 8051 Microcontroller is one microcontroller which is commonly used in various fields and devices created for those fields. This microcontroller holds immense importance in the field of electronics, and thus is necessary to learn about, rather than just learning the basics of other microcontrollers.

Every student has his or her strong points as well as his or her weaker points. What it comes down to is focusing on strengthening the weaker points while keeping the strong points steady as they are. Reference books will help a student understand better what he or she could not, because it is filled with information such as the applications, concepts and even case studies of all the topics of study at hand.

8051 Microcontroller is also such a subject where the student may face such problems. Some topics may be more difficult for some students, while the same topics will be simpler for other students to learn. Thus comes the need to focus on 8051 Microcontroller reference books.

Some 8051 Microcontroller reference books which would be of good use to students studying this microcontroller are contained in the list which follows.

A curriculum is the skeleton or outline for any subject. It allows the student to scour through the list of topics that make up a subject, and scout the weak and strong points in them which we mentioned about earlier. It is severely important to have an idea of what is easier to study and what is not, relatively speaking. The curriculum for a subject will allow you to do this.

The 8051 Microcontroller curriculum also serves the same purpose, of helping students try to figure out what is tougher and what is relatively easier. Additionally, when the 8051 Microcontroller curriculum is right in front of an electronics student, it makes sure that he or she misses out on no topic at all.

Below is the unit wise and topic wise breakdown of the 8051 Microcontroller curriculum.

The questions in the 8051 Microcontroller examination question paper are given module-wise. There are 10 questions (2 from each module) and the student must answer one question from each module worth 16 marks total. These questions can be either 4+6+6 marks, 8+4+4 marks, or 8+8 marks. All in all, there are 4 markers, 6 markers and 8 markers in the question paper to be answered.

4 Mark Questions

6 Mark Questions

8 Mark Questions

FAQ’s about 8051 Microcontroller Notes

Question 1. What are the applications of the 8051 Microcontroller?

Answer: The 8051 Microcontroller can be used to control various different kinds of devices, which include the following:

Question 2. What is a good textbook or reference boom I can use to study 8051 Microcontroller?

Answer: A great book for studying the 8051 Microcontroller is “The 8051 Microcontroller: A Systems Approach” which is written by Janice Gillispie Mazidi, Muhammad Ali Mazidi, and Rolin D McKinlay. This is a great book as it has also been recommended by several professors for this subject in different universities as well.

Question 3. What is the importance of the subject of the 8051 Microcontroller?

Answer:  By the end of a course in the 8051 Microcontroller, students will have a fairly practical knowledge about this microcontroller. Students will have understood the architecture and programming of the 8051 Microcontroller along with several other aspects. This subject holds great importance because this microcontroller is used in several fields, and studying it would enable students to understand the working behind machinery and devices used throughout a vast array of industries and sectors.

Question 4. What is the basic curriculum for the 8051 Microcontroller course?

Answer:  There are a total of 5 modules in the 8051 Microcontroller curriculum, which are:

We have provided you some great 8051 Microcontroller Notes, reference books, curriculum and important questions. These should hopefully be adequate to help you study and attain the ebay marks possible in your 8051 Microcontroller paper. We wish all students good luck for the exams and hope that the study materials we have provided in the above article have taken away any anxiousness or nervousness felt by the student. It is our sincere hope that you as a student use these study materials and resources to the best of your abilities. Doing so will ensure that you get the greatest marks, in the process making you, your parents and your family happy. You will also be able to get a great job by doing well, so make sure to use the 8051 Microcontroller Notes wherever possible!

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8051 Microcontroller | 8051 Microcontroller pin diagram, working, Construction.

Hey guys, welcome back to Techatronic. In this article, we will learn about the 8051 microcontroller and memory organization in it. 8051 is an 8-bit microcontroller designed by intel in 1981. It has a bidirectional data bus of 8 bits and a 16-bit unidirectional address bus.

There are two 16 bits timers/counters and four 8 bits input and output ports. The internal data memory of 8051 is divided into two groups. There are a set of 8 registers and a scratchpad memory. some people called it or search it by 8051 microprocessor . it is a microcontroller, not a microprocessor.


These eight registers are R0 to R7. It has 4 Kb of ROM and 128 bytes of RAM. You can read our articles on IoT and basic electronics . So let us start

Table of Contents

8051 Pin Diagram

8051 Pin Diagram

8051 Pin Description

It is the very famous 8051 microcontroller along with Arduino and ESP Family. But unlike both family It comes in DIP package and is a single or main component which requires to be programmed.

This 8051 can easily be programmed either using Arduino ICSP or using any other FTDI custom software. Tutorial for programming is also available, you can view it from Programming in 8051 .

It has 4 ports, 2 timers and 1 serial which can be used, But as it is very old controller no Modern communication like SPI, I2C or any other can be used.

Further we’ll discuss some pins and their functions, For more detailed information you can always refer to its datasheet .

PIN 1-8 : These are 8051 port pins, (PORT 1) with 8-bit Bi-Direction I/O, pull-up resistors and Schmitt trigger.

PIN 9 : It is the rest pin which is used to reset the microcontroller. To reset the chip, you have to make this pin HIGH for two machine cycles. Also connect an external capacitor with Vcc to this pin for power-on reset.

PIN 10-17 :These are also port pins (PORT 3) like 1-8 with 8-bit Bi-Direction I/O, pull-up resistors and Schmitt trigger. But unlike them these pins are for some special function which are discussed further:

PIN 10 ( RXD), : This is the serial Input Pin for receiving data during programming the chip.

PIN 11 (TXD), : This is the serial Input Pin for transmitting data during programming the chip.

PIN 12 (INT0), : External interrupt

PIN 13 (INT 1 ), : External interrupt

PIN 14 (T0), : Timer 0 external input

PIN 15 (T1), : Timer 1 external input

PIN 16 (WR), : External data memory write strobe

PIN 17 (RD), : External data memory read strobe

PIN 18-19 : these are the XTAL pins which are connected to external crystal oscillator.

PIN 20 : GND Pin connected to ground of the power supply.

PIN 21-28 : These are also port pins (PORT 2) like other two with 8-bit Bi-Direction I/O, pull-up resistors and Schmitt trigger.

PIN 29 (PSEN) : Program Store Enable , This pin is activated during reading memory strobe from external memory.

PIN 30 (ALE/PROG) : Address Latch Enable/Program Pulse , output pulse for latching the low byte of the address during access to external memory. In normal operation, ALE is emitted at a constant rate of 1/6 the oscillator frequency, and can be used for external timing or clocking.

PIN 31 (EA/VPP) : External Access Enable/Programming Supply Voltage , This pin is pulled low to enable the device to fetch code from external program memory locations.

PIN 32-39 : These are PORT 0 pins which are open-drain, bidirectional I/O port with Schmitt trigger inputs.

PIN 40 : This is the Vcc pin connected to high potential of the power supply.

it is a microcontroller, not a microprocessor. to understand the difference between the microprocessor and microcontroller . you need to read our embedded system article.

8051 microcontroller

Register Set of 8051 Microcontroller

8051 microprocessor

Memory Organization in 8051

Memory Organization in 8051

The memory organization in 8051 microcontroller is separated into program memory (ROM) and data memory (RAM). The program memory is used for storing the program to be executed i.e instructions. The data memory is used for storing temporary variable data and intermediate results. The internal RAM of 8051 is organized in three areas.

8051 microcontroller

We hope that you understand the working of an 8051 microcontroller and its memory organization completely. If you have any doubts regarding this post then use the comments section which is given below. Also, do check out more articles on Arduino and Raspberry Pi .

Thanks for learning

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The usefulness of Assembler Directives of 8051

There are four assembler directives mostly used in 8051 Microcontroller assembly programming. Let’s find the importance of directives with programming.

Table of Contents

DB (Define Byte)

The define byte (DB) is mostly used as a data directive in the 8051 assemblers. It is used to define data in decimal, binary, hexadecimal, and ASCII formats. In the case of the 8051 microcontroller, the size of the data is 8-bit.

Decimal Number

To define data in decimal use ‘D’ after the decimal number. For decimal symbol ‘D’ can be ignored also. For example

Hexadecimal Number

To define data in hexadecimal use ‘H’ after the hexadecimal number. For example

Binary Number

To define data in binary use ‘B’ after the binary number. For example:

ASCII Format

To define data in ASCII format use an inverted comma. For Example:

ORG (Origin)

ORG is another assembler directive of the 8051 Microcontroller. ORG directive is used to shows the beginning of the address for a particular code section. After the ORG directive 16-bit number comes which may be denoted in Hexadecimal or Decimal. For the hexadecimal, the letter ‘H’ is used. If the number is not followed by H then it will be assumed as a decimal and the assembler will convert it to Hex. For example, to start the assembly code with a 2000H location use following

EQU (Equate)

The EQU directive is used to define constant value without occupying the memory location. With the EQU directive, a constant value and label name are required. Whenever the label name appears in the program its constant value will be passed automatically. For example, we want to use constant value 10 regularly in the program so we can use the EQU directive to manage it efficiently.

In the above example, data10 will be loaded to the A register. Here # means that the data is in Immediate form. The programmer can change the value throughout the program with the use of the EQU directive. For example, if the programmer wants to change the constant value to 50 then it can be easily done in all occurrences of the program.

END (END Program)

The end directive indicates the end of the assembly code. The assembler will ignore content after the END directive and it is supposed to be used as the last line of the 8051 Microcontroller assembly code.

In this tutorial, we have discussed different assembler directives of the 8051 Microcontroller. To see the complete datasheet of 8051 follow this link.

People are also reading the difference between Microprocessor and Microcontroller tutorial.

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Set up Keil c51 for 8051 microcontroller simulations – A step by step guide

In our 8051 course , we will be using the Keil Microvision C51. It’s a free (conditions apply – See the box below) IDE for 8051 related embedded development and is a very popular simulation platform as well. You can simulate the code written in the IDE to see the transfer of data in memory locations and registers making it a great tool for simulation. I thas advanced debug capabilities too that makes it extremely powerful for testing.

Installing and setting up Keil C51 for 8051

Step 1: Head to the Keil C51 site to download the installation files for Keil C51 IDE. Once downloaded run the .exe file, and then launch the Keil C51 IDE.

keil setup

Step 6 : Create a new file by clicking on the new file button in the top right corner.

conclusion 8051 microcontroller

Step 10 : Select the file you created and add it here. Now you have a Project file with its constituent code files. All the other files that will be generated will be present in this Project folder.

keil setup step 10

Simulating code using Keil Microvision

keil simulation 1

Once you click here after compiling your code you can see a step by step execution of your code. Let’s get insights into how the addition of numbers happens inside the microcontroller using the simulator.

keil simulation 2

Now you can learn assembly language programming/embedded C with 8051 without actually needing a kit. Just take up any sample programs, compile them, and run the simulation tool. This is a great exercise in learning the working of instructions from a close perspective.

If you have any issues with installing the IDE, let us know in the comments.

Nischay Khanna

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8051 Microcontroller Architecture with Applications

The 8051 Microcontroller was designed in the 1980s by Intel. Its foundation was on Harvard Architecture and was developed principally for bringing into play Embedded Systems . At first, it was created using NMOS technology but as NMOS technology needs more power to function therefore Intel re-intended Microcontroller 8051 employing CMOS technology and a new edition came into existence with a letter ‘C’ in the title name, for illustration: 80C51. These most modern Microcontrollers need a fewer amount of power to function in comparison to their forerunners. There are many applications with an 8051 microcontroller. So, 8051 Microcontroller Projects have great significance in Engineering final year. This article discusses an overview of 8051 microcontroller architecture and its working.

What is an 8051 Microcontroller?

The microcontroller like 8051 was designed in the year 1981 by Intel. The microcontroller is one kind of integrated circuit that includes 40-pins with dual inline package or DIP, RAM-128 bytes, ROM-4kb & 16-bit timers–2. Based on the requirement, it includes addressable & programmable 4 – parallel 8-bit ports. In the 8051 microcontroller architecture, the system bus plays a key role to connect all the devices to the central processing unit. This bus includes a data bus- an 8-bit, an address bus-16-bit & bus control signals. Other devices can also be interfaced throughout the system bus like ports, memory, interrupt control, serial interface, the CPU, timers.

There are two buses in 8051 Microcontroller one for the program and another for data. As a result, it has two storage rooms for both programs and data of 64K by 8 sizes. The microcontroller comprises of 8-bit accumulator & an 8-bit processing unit. It also consists of 8 bit B register as majorly functioning blocks and 8051 microcontroller programming is done with embedded C language using Keil software. It also has several other 8 bit and 16-bit registers.

For internal functioning & processing Microcontroller, 8051 comes with integrated built-in RAM. This is prime memory and is employed for storing temporary data. It is an unpredictable memory i.e. its data can get be lost when the power supply to the Microcontroller switched OFF.  This microcontroller is very simple to use, affordable less computing power, simple architecture & instruction set.

The main features of the 8051 microcontroller architecture include the following.

8051 Microcontroller Architecture

The 8051 microcontroller architecture is shown below. Let’s have a closer look at the features of the 8051 microcontroller design:


CPU (Central Processor Unit):

As you may be familiar that the 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. The user has no power over the functioning of the CPU. It interprets the program printed in storage space (ROM) and carries out all of them and does the projected duty. CPU manages different types of registers in the 8051 microcontrollers .


As the heading put forward, Interrupt is a subroutine call that reads the Microcontroller’s key function or job and helps it to perform some other program which is extra important then. The characteristic of 8051 Interrupt is extremely constructive as it aids in emergency cases. Interrupts provide us a 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 the interrupt. When the sub-routine task is finished then the implementation of the core program initiates automatically as usual. There are 5 interrupt supplies in the 8051 Microcontroller, two out of five are peripheral interrupts, two are timer interrupts and one is serial port interrupt.

The micro-controller needs a program that is a set of commands. This program enlightens the Microcontroller to perform precise tasks. These programs need a storage space on which they can be accumulated and interpret by the Microcontroller to act upon any specific process. The memory which is brought into play to accumulate the program of the Microcontroller is recognized as Program memory or code memory. In common language, it’s also known as Read-Only Memory or ROM.

The microcontroller also needs 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 which has 4KB Rom and it also comprises data memory (RAM) of 128 bytes.

Fundamentally Bus is a group of wires which function as a communication canal or means for the transfer of Data. These buses comprise 8, 16, or more cables. As a result, a bus can bear 8 bits, 16 bits altogether. There are two types of buses:

As we all make out the Microcontroller is a digital circuit piece of equipment, thus it needs a timer for its function. For this function, Microcontroller 8051 consists of an on-chip oscillator that toils as a time source for the CPU (Central Processing Unit). As the productivity thumps of the oscillator are steady as a result, it facilitates harmonized employment of all pieces of the 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.

Types of Interrupts

The interrupts of the 8051 microcontrollers have the following sources

The memories of the 8051 microcontroller architecture include a program memory and data memory.

Timer and Control Unit

The main function of a timer is to make a delay otherwise time gap among two events. This microcontroller includes two timers where each timer is 16-bit where the system can generate two delays concurrently to produce the suitable delay. Generally, every microcontroller uses hardware delays where a physical device can be used through the processor to generate the particular delay which is called a timer.

The delay can be generated through the timer based on the requirement of the processor & transmits the signal to the processor whenever the particular delay gets generated.

By using this processor, we can also produce a delay based on the requirement of the system. However, this will guide to remain the processor active all the time because it will not perform any other task in that specific period. As a result, the existence of a timer within the microcontroller permits the processor to be free for performing other operations.

The microcontroller also includes a program counter, data pointer, stack & stack pointer, instruction registers including latches, temporary registers & buffers for the I/O ports.

Registers in microcontrollers are mainly used to store data and short-term instructions which are mainly used to process addresses to fetch data. This microcontroller includes 8-bit registers which have 8-bit start from D0 to D7. Here, D0 to D7 is LSB (least significant bit) and D7 is the most significant bit (MSB).

To make the data process better than 8-bit, then it must be separated into eight different bit parts. It includes several registers however general-purpose type registers are frequently available to programmers. There are classified into two types like General purpose & Special purpose. So, most of the general-purpose registers are listed below.

This microcontroller includes simply one 8 bit data type where the size of each register is 8-bit. If the data is better than 8-bit, then is the programmer accountable to separate data into 8-bit parts before processing. For assemblers, the most widely used data directive is the DB directive in assembly language.

PSW Register

The term PSW stands for Program status word and it is one kind of register in the microcontroller. It is also called a flag register, used to demonstrate the position of arithmetic logic instructions such as zero carry bit, carry bit, etc. PSW or flag register is an 8-bit register where 6-bits are used. This register includes 8-flags where these flags are known as conditional flags. These flags will perform instruction simply if the condition is satisfied.

These conditional flags are overflow, parity, auxiliary carry & carry. The Program status word registers bit numbers like 3 & 4 are used to alter the bank registers whereas 1 & 5 are not used but they can be used by the programmer for executing a specific task.

Register Banks

For stacks & register banks, Ram with 32 Bytes is used and these are separated in four types of banks. So, every back includes 8-registers which range from R0 to R7. Here, R0 & R7 denotes the locations of RAM like zero location and seventh location. The second bank register begins from location 8 & ends 05H. The third bank register begins from 10H & completed at the 17H location. The final bank can be placed among the 18H-1FH.

The part of RAM like Stack is mainly used through the processor for data storage otherwise address momentarily. In a microprocessor, it is a very significant part because there are extremely restricted numbers of registers for storing addresses and data.

In the 8051 microcontrollers, the stack is 8-bit wide and it can hold data from 00 – FFH. The stack pointer can be used through the CPU to allow the stack. This microcontroller includes an 8-bit stack pointer that means it can allow values from 00H to FFH. Once it is activated, then the stack pointer includes the 07 value.

Organization of Memory

The microcontroller has complex memory organization and it includes a separate address bus that is used for program memory, external RAM & data memory. It depends on Harvard architecture that is developed through Harvard in the year 1944.

Addressing Modes

Microprocessor gets data in different methods. Generally, the data stored within memory, register & can be used from instant value. So, these different methods for accessing data are known as addressing modes. Different types of microcontrollers include different addressing modes which depend on the plan of manufacturers. The addressing modes of this microcontroller include the following.

Applications of 8051 Microcontroller Architecture

The microcontroller 8051 applications include a large number of machines, principally because it is simple to incorporate in a project or to assemble a machine around it. The following are the key spots of the spotlight:

Applications of 8051 microcontroller

Thus, this is all about an overview of 8051 microcontroller architecture, working, and its applications. Here is a question for you, what are the different families available in the 8051 microcontrollers?

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Digital Thermometer using LM35 and 8051 Microcontroller

Digital Thermometer using LM35 and 8051

Sometimes people find it difficult to read temperature from analog thermometer because of fluctuations. So here we are going to build a simple Digital thermometer using 8051 microcontroller  in which LM35 sensor is used for measuring the temperature. We have also used LM35 to build digital thermometer using Arduino , NodeMCU , PIC , Raspberry Pi and other microcontrollers. 

This project will also serve as a proper interfacing of ADC0804 with 8051 and 16*2 LCD with 8051 microcontroller .

Components Required:                          

Circuit Diagram:

Circuit diagram for  Digital Thermometer Circuit using LM35  is given below:

Digital Thermometer circuit diagram using LM35 and 8051

Measuring Temperature with LM35 using 8051:

8051 microcontroller  is a 8 bit microcontroller which has 128 bytes of on chip RAM , 4K bytes of on chip ROM, two timers, one serial port and four 8bit ports. 8052 microcontroller is an extension of microcontroller. The table below shows the comparison of 8051 family members.

Block diagram of Digital Thermometer

16*2 LCD is a widely used display for embedded applications. Here is the brief explanation about pins and working of 16*2 LCD display. There are two very important registers inside the LCD. They are data register and command register. Command register is used to send commands such as clear display, cursor at home etc., data register is used to send data which is to be displayed on 16*2 LCD. Below table shows the pin description of 16*2 lcd.


The below table shows frequently used LCD command codes.

ADC0804 IC:

The ADC0804 IC is an 8-bit parallel ADC in the family of the ADC0800 series from National Semiconductor. It works with +5 volts and has a resolution of 8bits.  The step size and Vin range varies for different values of Vref/2. The table below shows the relation between Vref/2 and Vin range.

In our case Vref/2 is connected to 1.28 volts, so step size is 10mV. For ADC0804 step size is calculated as (2 * Vref / 2) / 256.

Following formula is used to calculate output voltage:

Where Dout is digital data output in decimal, Vin = analog input voltage and step size (resolution) is the smallest change. Learn more about ADC0804 here , also check interfacing of ADC0808 with 8051 .

LM35 Temperature Sensor:

The LM35 is a temperature sensor whose output voltage is linearly proportional to Celsius temperature. The LM35 comes already calibrated hence requires no external calibration. It outputs 10mV for each degree of Celsius temperature.

LM35 sensor produces voltage corresponding to temperature. This voltage is converted to digital (0 to 256) by ADC0804 and it is fed to 8051 microcontroller. 8051 microcontroller converts this digital value into temperature in degree Celsius. Then this temperature is converted into ascii form which is suitable for displaying. This ascii values are fed to 16*2 lcd which displays the temperature on its screen. This process is repeated after specified interval.

Below is the setup image for  LM35 Digital Thermometer using 8051:

Digital Thermometer in action using LM35 and 8051

You can find all the LM35 based digital thermometers here. 

Code explanation:

The complete C program for this Digital Thermometer using LM35 is given at the end of this project. The code is split into small meaningful chunks and explained below.

For 16*2 LCD interfacing with 8051 microcontroller , we have to define pins on which 16*2 lcd is connected to 8051 microcontroller. RS pin of 16*2 lcd is connected to P2.7 , RW pin of 16*2 lcd is connected to P2.6 and E pin of 16*2 lcd is connected to P2.5. Data pins are connected to port 0 of 8051 microcontroller.

Similarly, for ADC0804 interfacing with 8051 microcontroller, we have to define pins on which ADC0804 is connected to 8051 microcontroller. RD pin of ADC0804 is connected to P3.0, WR pin of ADC0804 is connected to P3.1 and INTR pin of ADC0804 is connected to P3.2. Data pins are connected to port 1 of 8051 microcontroller.

Next we have to define some functions which are used in the program. Delay function is used to create specified time delay, c mdwrt function is used to send commands to 16*2 lcd display, datawrt function is used to send data to 16*2 lcd display and convert_display function is used to convert the ADC data into temperature and to display it on 16*2 lcd display.

In below part of the code, we are sending commands to 16*2 lcd . Commands such as clear display, increment cursor, force the cursor to beginning of 1 st line are sent to 16*2 lcd display one by one after some specified time delay.

In this part of the code, we are sending data to 16*2 lcd . Data to be displayed on 16*2 lcd display are sent to display one by one after some specified time delay.

In below part of the code , we are sending commands to 16*2 lcd display. The command is copied to port 0 of 8051 microcontroller. RS is made low for command write. RW is made low for write operation. High to low pulse is applied on enable(E) pin to start command write operation.

In this part of the code, we are sending data to 16*2 lcd display. The data is copied to port 0 of 8051 microcontroller. RS is made high for command write . RW is made low for write operation. High to low pulse is applied on enable(E) pin to start data write operation.

In this part of the code, we are converting digital data into temperature and displaying it on 16*2 lcd display.

Also, check other thermometers using LM35 with different microcontrollers:

Done a gud job ,it's really

Done a gud job ,it's really superb

Awesome, keep it up.

Hey Really well written and described. Keep up the good work! All the best

Nice work.!!

temperature measurement

How to measure negative temperature by LM35

Its not possible with LM35

Proteus Simulation

Is it possible to use the code for Proteus Simulation? Thanks and more power.

yes , u can use same code for

yes , u can use same code for proteus simulation

project doubt

sir, we have dumped the program into the micro controller but its not working (no errors & no warnings) we didn't purchased the microcontroller development board instead we have built crystal oscillator &reset circuit to it what is the problem behind it ? can u rply to it as soon as possible

Are you sure the code is

Are you sure the code is uploaded correctly? If yes then try a basic blink program on your hardware and check if that is working properly 

Yes sir , we have checked it & the led is blinking but the temperature is not displaying on the lcd

Check your LCD connections

Check your LCD connections make sure the contrast pin of the LCD is set correctly using a pot

Impressive explanation helps a lot thanks.

We have implemented the

We have implemented the circuit and code as given, LCD is glowing but nothing is displaying on the LCD. Proteus simulation also gives the same result-glowing LCD but no display of characters. What is the problem? Please help us ASAP as it is required for our academic project.

The problem should be with

The problem should be with your hardware, check the contrast pin of the LCD

I have executed this circuit design in Proteus and have burnt the keil hex code onto the microcontroller. On running the simulation, there were no such errors found but it is not dusplaying an output on the LCD. What's wrong?

Check your hardware

Check your hardware connection, make sure your contrast level on LCD is set properly 

Yes read about that, tried

Yes read about that, tried all the possibilities, how exactly do I ensure what you're suggesting?

Is your LCD blank or showing

Is your LCD blank or showing black boxes? You shouldnotice your LCD from having black boxes to going blank when you set contrast level 

It brightens on running the

It brightens on running the simulation but is blank, no black boxes or anything like that

Is there some problem in the

Is there some problem in the code? Maybe that's why the display is not showing any readings and just glowing? Can someone please help me, it's urgent.

Facing the same problem! Did you get the solution ?

No I didn't! The project is

No I didn't! The project is done and submitted though. I would suggest follow some other site's code. Technically, if the code was right, it should have been successful in Proteus, it wasn't. So there's a glitch in the code. Either from your own code or refer to something else.

In your code, you are reading ADC data from port , storing it to variable value, and directly displaying it. You are not converting  ADC data to temperature. Please add the Data Convertion section. I am facing a problem in convertion

for 100 D Centi, ADC o/p is

for 100 D Centi, ADC o/p is 64 so first you will convert ADC out put to Decimal & then Decimal will be converted to ASCII to display it....right? Please reply if i am wrong.....

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Microprocessor Tutorial

Microcontrollers - 8051 Architecture

8051 microcontroller is designed by Intel in 1981. It is an 8-bit microcontroller. It is built with 40 pins DIP (dual inline package), 4kb of ROM storage and 128 bytes of RAM storage, 2 16-bit timers. It consists of are four parallel 8-bit ports, which are programmable as well as addressable as per the requirement. An on-chip crystal oscillator is integrated in the microcontroller having crystal frequency of 12 MHz.

Let us now discuss the architecture of 8051 Microcontroller.

In the following diagram, the system bus connects all the support devices to the CPU. The system bus consists of an 8-bit data bus, a 16-bit address bus and bus control signals. All other devices like program memory, ports, data memory, serial interface, interrupt control, timers, and the CPU are all interfaced together through the system bus.

8051 Architecture


8051 Microcontroller Architecture and Block Diagram with Applications

July 30, 2019 By admin

8051 Microcontroller Architecture

8051 Microcontroller Architecture

The 8051 Microcontroller is one of the basic types of microcontrollers, designed by Intel in 1980s. This microcontroller  was based on Harvard Architecture and developed primarily for use in embedded systems technology. Normally, this microcontroller was developed using NMOS technology, which requires more power to operate. Therefore,  Intel redesigned Microcontroller 8051 using CMOS technology and  their updated versions came with a letter C in their name, for instance an 80C51 it is an 8 bit microcontroller. These latest  Microcontrollers requires less power to operate as compared to their previous versions. The 8051 Microcontroller  has two buses and two memory spaces of 64K X 8 size for program and data units. It has an 8 bit processing unit and 8 bit accumulator units.

Following diagram is  8051 Microcontroller architecture . Let us have a look at each part or block of this Architecture of microcontroller.

8051 Microcontroller Architecture

Central Processor Unit (CPU)

As we know that the CPU is the brain of any processing device of the microcontroller. It monitors and controls all operations that are performed on the Microcontroller units. The  User has no control over the work of the CPU directly . It reads program written in ROM memory and executes them and do the expected task of that application.

As its name suggests, Interrupt is a subroutine call that interrupts of the microcontrollers main operations or work and causes it to execute any other  program, which is more important at the time of operation. The feature of Interrupt is very useful as it helps in case of emergency operations. An Interrupts gives us a mechanism to put on hold the ongoing operations, execute a subroutine and then again resumes to another type of operations.

The Microcontroller 8051 can be configured in such a way that it temporarily terminates or pause the main program at the occurrence of interrupts. When a subroutine is completed, Then the execution of main program starts. Generally five interrupt sources are there in 8051 Microcontroller. There are 5 vectored interrupts are shown in below

Out of these,  (INT0) ̅ and (INT1) ̅ are external interrupts that could be negative edge triggered or low level triggered. When All these interrupts are activated, set the corresponding flogs  except for serial interrupt,.The interrupt flags are cleared when the processor branches to the interrupt service routine (ISR). The external interrupt flags are cleared when the processor branches to the interrupt service routine,  provides the interrupt is a negative edge triggered whereas the timers and serial port interrupts  two of them are  external interrupts, two of them are timer interrupts and one serial port interrupt terminal in general.

Microcontroller requires a program which is a collection of instructions. This program tells microcontroller to do specific tasks. These programs require a memory on which these can be saved and read by Microcontroller to perform specific operations of a particular task. The memory which is used to store the program of the microcontroller is known as code memory or Program memory of applications. It is known as ROM memory of  microcontroller also requires a memory to store data or operands temporarily of the micro controller. The data memory of the 8051 is used to store data temporarily for operation is known RAM memory. 8051 microcontroller  has 4K of code memory or program memory,that  has 4KB ROM and also 128 bytes of data memory of RAM.

Basically Bus is a collection of wires which work as a communication channel or medium for transfer of Data. These buses consists of 8, 16 or more wires of the microcontroller. Thus, these can carry 8 bits,16 bits simultaneously. Hire two types of buses that are shown in below

Address Bus : Microcontroller 8051 has a 16 bit address bus for transferring the data. It is used to address memory locations and to transfer the address from CPU to Memory of the microcontroller. It has  four addressing modes that are

Data Bus : Microcontroller 8051 has 8 bits of  the data bus, which is used to carry data of particular applications.

Generally, we know that  the microcontroller is a device, therefore it requires clock pulses for its operation of microcontroller applications. For this purpose, microcontroller 8051 has an on-chip oscillator which works as a clock source for Central Processing Unit of the microcontroller. The output pulses of oscillator are stable. Therefore, it enables synchronized work of all parts of the 8051 Microcontroller.

Input/Output Port

Normally microcontroller is used in embedded systems to control the operation of machines in the microcontroller. Therefore, to connect  it to other machines, devices or peripherals we require I/O interfacing ports in  the microcontroller interface. For this purpose microcontroller 8051 has 4 input, output ports to connect it to the other peripherals


8051 microcontroller has two 16 bit timers and counters. These counters are again divided into a 8 bit register. The timers are used for measurement of intervals to determine the pulse width of pulses.

Please refer to this link to know more about 8051 Microcontroller MCQs .

Applications of 8051 Microcontroller

Some of the applications of 8051 is mainly used in daily life & industrial applications also some of that applications are shown below

Some industrial applications of micro controller and its applications

Some of 8051 microcontroller devices are used in measurement applications

8051 Microcontroller Applications in Embedded Systems

The applications of 8051 microcontroller involves in 8051 based projects. The list of 8051 projects is listed below.

Please refer to this link to know more about ARM Architecture MCQs & Microcontrollers MCQs

Do you have any innovative ideas to implement the 8051 microcontroller based electronics projects? Then, feel free to share your ideas for getting your project solutions from us and also other readers, by posting in the comments section below.

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AT89c51 Microcontroller: Programming, Pinout, Features, and Alternatives

Atmel AT89 series fall under the 8-bit microcontroller family compatible with Intel 8051. Their advantages include cost-effectiveness and high flexibility when used in embedded control applications. Examples of the chip under the series are AT89C2051, AT89C51, etc. For today, we’ll discuss the AT89C51 microcontroller. 

What is the AT89C51 Microcontroller?

AT89C51 is a CMOS 8-bit microcontroller of high performance but low power. Further, it has an erasable and flashes programmable (4K bytes) EPROM .  


Manufacturers use the high-density nonvolatile memory technology of an Atmel to produce a powerful microcomputer. Moreover, it’s often conjunction with pinout and set instructions from MCS-51 industry standards. 

AT89C51 Pinout

The table below summarizes the pin configuration of AT89C51. 

At89c51 pinout 

At89c51 pinout 

conclusion 8051 microcontroller

Features of Microcontroller

The features and specifications of at89c51 comprise the following;


They are as follows;

How to Program the AT89C51 (8051) Microcontroller

You can use software like Keil µVision or Arduino to program AT89C51 . We’ll also need a programming environment like an Integrated Development Environment (IDE), USBASP programmer, and MAX232 programming hardware. You’ll purchase all the components separately. 

How to select your Atmel Microcontroller?

Undeniably, there are several microcontrollers from Atmel and PIC families, all with advantages and disadvantages. Choosing the best one for your project, therefore, requires a good criterion. 

The list below gives examples of the factors you can consider.


Some applications of at89c51 include;

Arduino UNO microcontroller

(Arduino UNO microcontroller)

That sums up our at89c51 article. For further inquiries or questions, kindly contact us . 

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conclusion 8051 microcontroller

8051 Microcontroller Introduction and Basics

This article is about the 8051 Microcontroller Introduction and some of its basic features. The 8051 Microcontroller is one of the most popular and most commonly used microcontrollers in various fields like embedded systems, consumer electronics, automobiles, etc.

Technically called as Intel MCS-51 Architecture, the 8051 microcontroller series was developed by Intel in the year 1980 and were very popular in the 80’s (still are popular).

8051 Microcontroller has many features like Serial Communication, Timers, Interrupts, etc. and hence many students and beginners start their work on the concept of Microcontrollers with 8051 Microcontroller (although this trend seems to be changed with the introduction of Arduino).

Even though 8051 Microcontroller might seem a little bit out of fashion, we feel that it is one of the best platforms to get started with Microcontrollers, Embedded Systems and Programming (both C and Assembly). 

8051 Microcontroller Introduction Image 1

So, in this post, you’ll be given an introduction to 8051 microcontroller and some of the basics of 8051 Microcontroller.

But before going in to the Introduction and Basics of 8051 Microcontroller, we need to a little bit about what a Microcontroller is and Difference between Microprocessor and Microcontroller.

The Differences between Microprocessor and Microcontroller are tabulated in this post. 

What is a Microcontroller?

A Microcontroller is a VLSI IC that contains a CPU (Processor) along with some other peripherals like Memory (RAM and ROM), I/O Ports, Timers/Counters, Communication Interface, ADC, etc.

8051 Microcontroller Introduction Image 2

On the contrary, a Microprocessor (which was developed before Microcontroller) is just a Processor (CPU) and doesn’t have the above mentioned peripherals. In order to make it work or build a system around it, we need to interface the peripherals separately.

8051 Microcontroller Introduction Image 3

Until the development of Microcontrollers, almost all process and control tasks were implemented using Microprocessors. As Microprocessor need the additional peripherals to work as a system, the overall cost of the control system was high.

But with the development of Microcontroller, the situation has changed completely including the world of Embedded Systems.

8051 Microcontroller Introduction and History

The 8051 Microcontroller Introduction gives a brief overview about the 8051 Microcontroller and its history. Intel’s 8051 Microcontroller (Intel MSC-51 Architecture) was a successor to 8048 Microcontroller (Intel MSC-48 Architecture).

Originally, 8051 Microcontrollers were developed using N-MOS Technology but the use of battery powered devices and their low power consumption lead to usage of CMOS Technology (which is famous for its low power consumption).

Even though Intel developed 8051 Microcontrollers (which is discontinued in 2007), more than 20 semiconductor manufacturers are still producing 8051 compatible microcontrollers i.e. processors based on MSC-51 Architecture.

Some of the 8051 Microcontrollers produced by different manufacturers are: Atmel (AT89C51, AT89S51), Phillips (S87C654), STC Micro (STC89C52), Infineon (SAB-C515, XC800), Siemens (SAB-C501), Silicon Labs (C8051), NXP (NXP700, NXP900), etc.

Majority of the modern 8051 Microcontrollers are Silicon IP Cores (Intellectual Property Cores) but discrete 8051 Microcontroller IC’s are also available. Because of their low power consumption, smaller size and simple architecture, 8051 IP Cores are used in FPGAs (Field Programmable Gate Array) and SoCs (System on Chip) instead of Advanced ARM Architecture based MCUs.

Applications of 8051 Microcontroller

Even with the development of many advanced and superior Microcontrollers, 8051 Microcontroller is still being used in many embedded system and applications.

Some of the applications of 8051 Microcontroller are mentioned below:

8051 Microcontroller Basics

8051 is an 8 – bit Microcontroller i.e. the data bus of the 8051 Microcontroller (both internal and external) is 8 – bit wide. It is a CISC based Microcontroller with Harvard Architecture (separate program and data memory).

Since the basic layout of a microcontroller includes a CPU, ROM, RAM, etc. the 8051 microcontroller also has a similar layout. The following image shows a brief layout of a typical 8051 Microcontroller.

8051 Microcontroller Introduction Image 4

8051 Microcontroller Features

NOTE : Some of the features like size of RAM and ROM, number of Timers, etc. are not generic. They vary by manufacturer.

8051 Microcontroller Packaging

8051 Microcontroller is available in a variety of IC Packaging Types. The most popular and commonly used 8051 Microcontroller Packaging is Dual in-line or DIP. It is often available as a 40 – pin PDIP or Plastic DIP IC.

The other common packaging type is 44 – Lead PLCC (Plastic Leaded Chip Carrier). It is a kind of surface mount package.

Another surface mount packaging for 8051 microcontroller is 44 – Lead TQFP (Thin Quad Flat Package).

This article gave an introduction to 8051 Microcontroller and some its basic features. In the next article, we will see the Pinout Diagram, Pin Description and Architecture of 8051 Microcontroller.

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10 Responses

Very knowledgeable

Ty so much for this kind of easy notes. It’s really best and simple to understand.

Thanks much buddy

Very good information with easy language.Thanks

Hi, quite sentimental article: I wrote Masters thesis on Motorola 6800 microcontroller simulation on ICL 1900 mainframe, but yet in 1979, year before 8051 was born … Nothing has changed apart the world.

it is very useful for easy understanding of the basics

Its awesome to learn and understand in a easy way thank you thank you very much

this information is very helpful for me thank u so much

Very nice and short presentation. Very helpful for the beginners, Thanks

Very well written series. Much easier to read than the original product manual. I could have made very good use of this series when I started using the 8051 in 1990. Since then I have designed and built several machine controllers. My background is Avionics technician (35years) & Industrial / University Electronics Tech. I have been the compiler / subject author of a complete aircraft maintenance manual. Now retired, I’m still messing with electronics.

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Digital Door Lock – Password based Electronic Code Lock using 8051 var cid = '4751671870'; var pid = 'ca-pub-4648753796436329'; var slotId = 'div-gpt-ad-circuitstoday_com-box-3-0'; var ffid = 1; var alS = 1002 % 1000; var container = document.getElementById(slotId); var ins = document.createElement('ins'); ins.id = slotId + '-asloaded'; ins.className = 'adsbygoogle ezasloaded'; ins.dataset.adClient = pid; ins.dataset.adChannel = cid; ins.style.display = 'block'; ins.style.minWidth = container.attributes.ezaw.value + 'px'; ins.style.width = '100%'; ins.style.height = container.attributes.ezah.value + 'px'; container.style.maxHeight = container.style.minHeight + 'px'; container.style.maxWidth = container.style.minWidth + 'px'; container.appendChild(ins); (adsbygoogle = window.adsbygoogle || []).push({}); window.ezoSTPixelAdd(slotId, 'stat_source_id', 44); window.ezoSTPixelAdd(slotId, 'adsensetype', 1); var lo = new MutationObserver(window.ezaslEvent); lo.observe(document.getElementById(slotId + '-asloaded'), { attributes: true });

As the world grows to be digitally dependent, even doors can now be designed to be secure and safe. The digital version of the lock and key holds a lot of promising features. The digital door lock is securely placed with passwords. However, this may also attract unethical hackers, therefore, an extra layer of security is also required. In this electronics project-based article, we have created a digital door lock that is controlled using a basic controller, the 8051 microcontrollers. The aim of this article is to understand the fundamental working principle behind a digital door lock.

What is a Digital Door Lock?

The Digital Door Lock in general is a password-based electronic code lock. In this project, we have designed the digital door lock using an 8051 microcontroller, a keypad, and a 12-volt dc relay. In this article, we have designed a simple digital door lock using 8051 -which can be used as a security checking system to limit access to an area/room only for certain individuals with the password. So our digital door lock project can be called with a very wide range of names like a digital combination lock using 8051 or a digital security code lock using 8051 microcontrollers or a password security system using 8051 or an electronic code lock or a digital code lock using 8051. People call this kind of a “ security system ” with different names, though all of them mean to build a basic password-based security system using a microcontroller like 8051 or AVR or PIC or Arduino (a controller of choice) with extra features like automatic door lock/opening facility, sound alarm, GSM based SMS alert, etc.

Digital Door Lock – Project Summary

Note:- We have a wonderful collection of 8051 projects which we have designed and published previously. Take a look If you are interested in building 8051 based applications and systems yourself! It’s a lot of fun to learn and build new kinds of stuff.

Let’s get to building our password-based digital door lock now. The circuit diagram of the digital code lock is given below. Assemble the circuit as shown in the diagram.

Password based Digital Door Lock/Electronic Code Lock – Circuit Diagram

Digital Door Lock using 8051 - Electronic Code Lock using 8051

Components Used

Connections explained.

Make the connections of the digital code lock project as shown in the circuit diagram. We have explained the connections below.

Keypad to 8051 – In this particular electronic code lock project, we have interfaced a 4×4 keypad to Port 3 of 8051 microcontroller. Row pins are connected from P3.0 to P3.3, whereas Column pins are connected from P3.4 to P3.7. Read our tutorial on interfacing keypad to 8051 – to learn how keypad is connected to 8051 and how keypresses are identified and displayed.

16×2 LCD Module to 8051 – We are using a 16×2 lcd module to display the status messages of the project. We have connected this LCD module in 8 bit mode (using 8 data lines). The 8 data lines are connected to Port 0 of 8051. An external pull-up resistance is connected using a 10K Resistor Network (with 8 pins) at Port 0 to interface the 8 data lines of LCD. The LCD controlling pins RS, R/W, and E are connected to Port 2 pins P2.7, P2.6, and P2.5 respectively.  Read our tutorial on interfacing LCD to 8051 – to learn how to connect the LCD module to 8051 properly and also to learn how to display text messages on the LCD module perfectly.

Push button switch – is used to setup reset circuit of 8051 and Crystal is used to provide necessary clock to 8051.

Working of the Digital Door Lock Circuit

The objective of the Digital Door Lock project is to allow access to people who input the 5 digit password correctly and to not allow access to people who input passwords wrongly. We use a 4×4 Keypad to input digits to the microcontroller and a 12V relay is used to control the electronic solenoid lock (not shown in the circuit diagram) of the door. The password is stored inside the 8051 programs (program memory). In the example program given below, we use password 12345 and is stored in the program memory location with the label – PASSW.

Program/ Code – Password Based Security System

The program is written in assembly language. The important aspects and subroutines of the program are explained below.

KEY_SCAN – is the subroutine to identify a keypress. The method of column scanning is employed in identifying the pressed key. The pressed key is identified and is assigned a decimal equivalent value (ASCII value) of the pressed key. You may read the tutorial on the keypad to 8051 – interfacing to learn more about programming.

READ_KEYPRESS – is the subroutine to collect user inputs. A counter is set up using register R0 to count 5 times (this will limit the user input collection to the first 5 key presses). Register R1 is assigned address location 160D. The collected user inputs are saved in address location starting from 160D. This location is incremented successively using INC R1 – command of 8051. So first user input is stored in 160D, second user input in 161D, third in 162D, fourth in 163D, and fifth user input in 164D. These address locations are accessed using register R1 via the indirect addressing method .

Note:- There are two delay routines written in the program. DELAY1 – is used as a delay for outputting messages on the LCD module properly. After sending a message/data to the LCD module, DELAY1 is called so that the message stays on the LCD screen for the stipulated delay time. DELAY2 (is a 2.5 seconds delay) is used to provide the necessary debouncing effect for the keypad. (A push-button switch or any kind of mechanical switch has a bouncing effect . This effect has to be nullified either with a capacitor or with some tweaks inside the software – for example – a 1 or 2 seconds delay after a key press is scanned)

CHECK_PASSWORD – is the subroutine to compare user input password (5 digits) with the actually stored password in the program. Comparison is made digit by digit by selecting each digit from stored password with the help of DPTR and loading it to Accumulator (with MOVC A,@A+DPTR). Each digit loaded to the accumulator is then compared with the corresponding digit stored as user input (in address locations 16D to 164D) by loading them one by one to register R1. Digits are compared by X-OR ing them with command XRL A,@R1. Based on the outcome of the comparison, this subroutine has commands written to either allow access (and turn ON relay) or to not allow access and display an “Access Denied” message on the LCD screen.

So that’s all about the Password-based Security System using 8051. We hope you have understood the circuit, it’s working, and the program really well. If you have any doubts, please ask in the comments section.  If you would like to learn more interesting and similar projects like this electronic password lock, take a look at the following security system/lock projects.

RFID-based Security System using 8051 – is a security system very similar to Digital Door Lock or Electronic Code Lock in concept. The major difference in this project is that unique RFID Tags are used to identify authorized personnel (instead of keypad and password). An RFID  reader is interfaced to 8051 to read RFID Tags.

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Interfacing external memory eeprom to 8051 microcontroller, learn to build real time clock using 8051and ds1307 rtc module, interfacing nokia 5110 display to 8051 micro controller, 37 comments.

only the lcd is glowing . Nothing is displayed on screen.

Plz send the pcb layout

If motor burns then how will you open the door

Whether the resistors and capacitors would be available in the development board? or do we need to connect it externally to the cicuit??

There is no source of 5 v in circuit For vcc

Will u please say me the Correct password as per above given program????

Please provide program code.hex

the relay part is not working for me can any one help me

How to interface the motor

I am not getting 4th line… Can anyone help me SEL EQU 41H

hello .. i wan to know.. how to add the password digit.. for example.. i want to use 6 or 8 digit for my password.. i really want to know to solve my problem in my mini project… thank you.. i need your help………….

where to add a buzzler

1)can anyone tell me that how, i can upload this program to 8051 2)and how i can change the password

how to burn assembly language in 8051 ..someone please tell the procedure (full instruction) [email protected]

Plz..provide program in C language..

thanku very much for very useful work

please provide the code in C-language

what is function for TMOD,TH1,SCON and also SEL EQU 41H

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