What is Micro-controller 8051/8bit/16bit/32bit

The Intel MCS-51 (commonly termed 8051) is an internally Harvard architecture, complex instruction highly programmed and set computing (CISC) instruction set. The first microcontroller single chip (µC) series has been  developed by Intel in 1980 for use in the purpose of embedded systems and robotic feilds. The First Intel’s original versions were popular in the 1980s and very early 1990s and enhanced binary compatible and derivatives remain popular today in Global world.

MCS-51 Intel’s original family has been developed by using N-type metal-oxide-semiconductor materials (NMOS) technology like its harbinger Intel MCS-48, but on later versions, defined by a letter C in their name (e.g., 80C51) used as metal–oxide–semiconductor material (CMOS) .In this technology it consume less power than their NMOS . This made is more suitable and compatible for powered battery devices.

The Microcontroller family was being continued in 1996 with the enhanced 8-bit MCS-151 and the 8/16/32-bit MCS-251 family of binary compatible microcontrollers and yet this generation is continue in search of extensive Technology.

A microcontroller is an economical on-chip built-computer which is used for doing some special task. Such as displaying and receiving information through led or remote controller device.

A microcontroller is a integrated circuit in which inbuilt memory is present. It contains micro processor, memory, input-output peripherals pin, analog to digital convertor, timer, counter, RAM etc. A microcontroller is also known as single chip computer because it has single silicon chip with memory is present. It has EEPROM for non volatile data storage, circuit for reset, power up, serial programming.


Architecture of microcontroller:

In microcontroller there is two type of processor first one is Von-Neuman architecture and second is Harvard architecture. Both the architecture is different.

Von-neuman architecture

In this type of microcontroller has single “data” bus. That is used to fetch both instruction and data. Program instruction and data are store in a same main memory. The main advantage is that it simplifies the microcontroller design because one memory is accessed.

Harvard architecture

In this type of microcontroller has separate data bus and instruction bus. It has 16 bit address bus (each has RAM & ROM) and 8 bit data bus. This allow execution to occur in parallel. As an instruction is being “pre-fetched”, the current instruction is executing on the data bus. once the current instruction is complete, the next instruction is ready to go. This pre-fetch theoretically allows for much faster execution then Von-Neuman architecture.



Microcontroller is used in products that are controlled automatically.

The various products that makes use of microcontroller in our everyday life are given below:

  1. Home: Television, DVD player, telephone, fax machine, cellular phones, security system, camera, sewing machine, musical instrument, exercising machine, video games, computer, microwave oven.
  2. Office: Computers, printer, telephones, Fax machine, security system.


Block diagram of microcontroller

 Block Diagram of 8051 microcontroller.png

Click Here : For Watch the Video Understand Well Step By Step

Microcontroller has instruction set

  1. CISC (complex instruction set computer):- This is an instruction set which supports many addressing mode for arithmetic and logical instruction , data transfer and memory accesses instruction.
  2. RISC (Reduced Instruction set computer):- this is an instruction set which supports fewar adderesing modes for the arithmetic and logical instruction and for data transfer instructions.


Interrupts in microcontroller

Interrupts is a input to a processor that indicates the occurrence an event. when an interrupt occur in controller jump to the location associated with that interrupt  and execution from their.


In the microcontroller it contains five interrupts

  1. TF0 & TF1
  2. INT0 & INT1
  3. Serial communication interrupts RX & TX
  4. Nested interrupt
  5. Software interrupts


Features of microcontroller:

  1. It is a 40 pin IC.
  2. It operates at power supply +5v.
  3. It has four port with 8 pin each.
  4. It has two timer counter.
  5. It has 128 byte of on chip data memory.
  6. It has 32 bidirectional input output lines.
  7. It has 8 bit flag register.
  8. It has general purpose RAM whose address varies from30Hz to 7FHz.
  9. It can perform binary or decimal arithmetic.


Types of microcontroller

The 8 bit microcontroller- when the ALU performs arithmetic and logical operation on a byte (8 bits) at an instruction, the microcontroller is an 8 bit microcontroller. the internal bus width of 8-bit microcontroller.

The 16-bit microcontroller:- When the ALU performs arithmetic and logical operations on a word (16-bits) at an instruction, the microcontroller is an 16-bit microcontroller. The internal bus width of 16-bit microcontrollers is of 16-bit. It has more computing capability and performance as compare to 8-bit microcontroller.

The 32-bit microcontroller- When the ALU performs arithmetic and logical operation on a double word (32-bits) at an instruction, the microcontroller is a 32-bit microcontroller is of 32-bit. The performance and computing capability of 32 bit microtrollers are enhanced with greater precision as compared to the 16-bit microcontrollers.


8051 microcontroller:

  1. 8051 Microcontroller family
  2. The member of microcontroller family is 8051 it is also known as MCS-51, 8052, 8031
  3. 8052- This microcontroller has 256 byte of RAM and 3 timers. it has standard features as compare to 8051 and it has an added 128 bytes of RAM and timer. It has 8k byte of on chip program ROM.
  4. 8031- This microcontroller has all features of 8051 but it has not ROM. In this microcontroller an external ROM that can be as large as 64k byte should be programmed and added to this for chip execution. it has only two port is input output port and rest two ports are used for external port.

Comparison of 8051 family members

Features 8051 8052 8031
RAM(bytes) 128 256 128
ROM 4k 8k 0k
Timers 2 3 2
Serial port 1 1 1
I/O pins 32 32 32
Interrupt source 6 8 6


8051 microcontrollers use two different kinds of memory such as UV-EPROM, Flash and NV-RAM.

  1. 8751- it is the UV-EPROM version of 8051. The 8751 is only 4k byte of UV-EPROM. It required to access to the PROM burner and the UV-EPROM eraser to erase the contents inside the chip before it is program again.
  2. AT89c51 from Atmel corporation- Atmel fabricated the flash ROM version of 8051 which is also known as at89c51.the flash memory can erase the contents within seconds.


Ram/Rom/Flash Configuration of  8951 Microcontroller

Part No ROM RAM I/O pins Timer Interrupt Vcc Packaging
At89c51 4k 128 32 2 6 5v 40
At89c52 8k 256 32 3 8 5v 40
At89c1051 1k 64 15 1 3 3v 20
At89c2051 2k 128 32 3 8 3v 20
At89LV51 4k 128 32 2 6 3v 40
At89LV52 1k 128 32 3 8 3v 40


Pin Descriptions of 8051 Microcontroller



Pin Working with Description:

PIN P1.0-P1.7 :-

Port 1 contains pin 1 to pin 8.port 1 is connected at these pins. It is a 8 bit port. It can be used as an input or output port. If these pins are high i.e 1 then port 1 act as input port and when these pins are low i.e 0 then port 1 acts as output port.

PIN 9 (reset):-

This pin is used reset the controller for resetting the 8051.

PIN 10-17:-

Port 3 is connected at these pins & it is also a 8 bit input output port. These pins are multifunctional.

PIN 10 (RXD)

External serial data is received at this pin.

PIN 11 (TXD) :-

This pin is used for transmitting serial data from microcontroller to external device.

PIN 12 & 13(INTO/INT1) :-

The external interrupts from hardware is applied through these pin.

PIN 14 & 15 (T0 & T1):-

The input of timer and counter is applied through these pins.

PIN 16 (WR)

This pin enables external data to be written with data generated by hardware.

PIN 17(RD):-

The data is read from external memory.

PIN 18 (XLT1,XLT2):-

The external oscillator is connected at these pin for generating internal clock signal.

PIN 20:-

The pin is connected to ground.

PIN 21 to 28:-

Port 2 is connected at these pin the output of port 2 are used to access external memory. Port 2 o/p high order byte of external memory.

PIN 29 (PSEN):-

PSEN stands for program Store Enable. It is active low control signal used to activate the enable signal of external ROM/EPROM.

PIN 30(ALE):-

ALE stands for Address Latch Enable. Two demultiplex AD0 to AD7 and external latch and ALE signal of 8051 is used.

PIN 31 (EA):-

EA stands for external access. When EA is active all the addresses fetched by the program are given to external ROM/EPROM.

PIN 32 to 39:-

It can be used as input output pins.  These pins are used to access external memory. At these pins multiplex low order address and data lines are present.

PIN 40:-

This pin is connected to power supply +5v.


Click Here : For Watch the Video Understand Well Step By Step



So, Friends I hope you understand this Topic very well . In upcoming Tutorial  I will be back with some new interesting Projects and we will discuss about some useful development topics. Here if you want to recommend that what I should write in upcoming Tutorial then please leave your comments. and if u need any help or query please don’t Hesitate to discuss with me. Thank You 🙂


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3 thoughts on “What is Micro-controller 8051/8bit/16bit/32bit

  1. Hi Enamul,
    Thanks for this concise explanation of micro controllers. It is very helpful for beginners like me. Can you please suggest some ways to read the datasheet of MC? How should one proceed to intuitively understand the important details by going through the datasheet of the specific micro controller board?

    Thanks in advance!

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