8051 Microcontroller Architecture and Application


The 8051 Microcontroller is one of the most commonly used microcontrollers, designed by Intel  in 1981. It is used in various fields like embedded systems, consumer electronics, robotics, remote controls, automotive industry, telecom applications, power tools etc. Here in this article we are going to study  the architecture and applications of 8051 microcontroller.

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What is a Microcontroller ?

A microcontroller is a programmable integrated circuit (IC) that consists of a small CPU, RAM and I/O pins. Microcontroller units (MCUs) are widely used in many devices.

8051 Microcontroller

8051 also known as MCS-51 is one of the most popular microcontroller.

Initially, it was created using NMOS technology but since NMOS technology needs more power to function therefore later Intel introduced a new version of 8051 microcontroller based on CMOS technology and this  new edition is called 80C51. These most modern Microcontrollers need a fewer amount of power to function in comparison to their forerunners.

8051 is an 8-bit microcontroller that includes 40-pins with dual inline package or DIP, 128 bytes RAM, 4-kb ROM and two 16-bit timers. It also includes four parallel 8-bit ports that are programmable and addressable based on the requirement. It also has an on-chip crystal oscillator of frequency 12 MHz integrated in it.

8051 Architecture

The block diagram of 8051 microcontroller architecture is shown below. Let’s discuss each unit briefly :

CPU (Central Processing Unit)

As you already know, 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.  It interprets the program printed in storage space (ROM) and carries out all of them and does the projected duty. It also manages different types of registers in the microcontroller.


Interrupt is a subroutine call that temporarily suspends the Microcontroller’s main program and helps it to perform some other program which is more important than that at that particular time and resume the main program where it had left it off.

Interrupts provide us a method to postpone the current process, carry out a sub-routine task and then all over again restart standard program implementation.

8051 has 5 interrupt sources, out of which two are peripheral Interrupts, two are timer interrupts and one is a serial port interrupt.


A program is a set of commands, which is needed by the Microcontroller to perform a particular task. These programs need a storage space where they can be stored and later  the microcontroller interpret them and perform the specific task.

8051 microcontroller architecture include two types of memory, such as : program memory and data memory.

  • The instructions of the CPU are stored in the Program Memory. It is usually implemented as Read-Only Memory or ROM, where the Program written into it will be retained even when the power is down or the system is reset.
  • Data Memory in a Microcontroller is responsible for storing values of variables, temporary data, intermediate results, and other data for the proper operation of the program.


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

  • Address Bus: Microcontroller 8051 consists of a 16-bit address bus. It is used to address memory positions. It is also utilized to transmit the address from the CPU to Memory.
  • Data Bus: Microcontroller 8051 consists of 8 bits data bus. It is used to cart data.


Microcontroller 8051 consists of an on-chip oscillator that functions as a time source for the CPU . It allows the operations inside the microcontroller and other parts to be synchronous.

Input/Output Port

8051 consists of 4 parallel ports of 8 bit each thereby providing 32 input-output pins. All the 4 ports function bidirectionally i.e., either input or output according to the software control.


Timers are used to create a time gap or delay between two events. The timer produces the delay according to the demand of the processor and sends the signal to the processor once the respective delay gets produced.

Microcontroller 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.

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

Features of 8051 Microcontroller

Let’s discuss the common feature of 8051 microcontroller:

  • An 8-bit CPU with two registers A (ACC or accumulator) and B
  • Internal Flash ROM of 8KB – It is a flash memory that supports in – system programming.
  • Internal RAM of 256 bytes – The first 128 Bytes of the RAM i.e. 00H to 7FH is again divided in to 4 banks with 8 registers (R0 – R7) in each bank, 16 bit addressable registers and 80 general purpose registers. The higher 128 Bytes of the RAM i.e. 80H to FFH consists of  Special Function Registers (SFR) which are used to control different peripherals such as Timers, Serial Port, all I/O Ports, etc.
  • 32 I/O Pins  – Arranged as 4 Ports: P0, P1, P2 and P3
  • 8-bit Stack Pointer (SP) and Processor Status Word (PSW)
  • 16-bit Program Counter (PC) and Data Pointer (DPTR)
  • Two 16-bit timers – T0 and T1
  • Interrupts – Two external and three internal
  • Oscillator and clock circuit
  • Serial Data Transmitter and Receiver for Full-Duplex operation – SBUF
  • Control Registers – SCON, PCON, TCON, TMOD, IP and IE

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:

  • Consumer Appliances (TV Tuners, Remote controls, Computers, Sewing Machines, etc.)
  • Home Applications (TVs, VCR, Video Games, Camcorder, Music Instruments, Home Security Systems, Garage Door Openers, etc.)
  • Communication Systems (Mobile Phones, Intercoms, Answering Machines, Paging Devices, etc.)
  • Office (Fax Machines, Printers, Copiers, Laser Printers, etc.)
  • Automobiles (Air Bags, ABS, Engine Control, Transmission Control, Temperature Control, Keyless Entry, etc)
  • Aeronautical and Space
  • Medical Equipment
  • Defence Systems
  • Robotics
  • Industrial Process and Flow Control
  • Radio and Networking Equipment
  • Remote Sensing