Block Diagram of 8051 MicroController


MicroController is differ from microprocessor , 8051 microcontroller is the most popular micro controller in the electronics industry. Compare to microprocessor , micro controller has it’s RAM ,I/O ports, Timers/Counters and communication interface. Whereas microprocessor Contains IC’s.

Basic Components of Microcontroller.

The following diagram illustrates the basic components of Micro Controller.

Fig (From Quora)

Micro Controller Contains various components like CPU , RAM ,ROM , Timer , Bus control etc.

Each and every component is explained below.


Stands for Central Processing Unit , Main part in PC/Micro Controller handles all task and co ordinates the resource among the parts. It executes the instructions ,which are loaded into the main memory. It has microprocessor to do the ob.


Known as Random Access Memory , very important to make the system working ,any instruction want to execute I,e want CPU, should be loaded first into the RAM.


Read Only Memory , It contains the instruction ,required for booting the system or micro controller . Hear data is not volatile means even though the power breakdown takes place during the execution, the instructions will not be erased.

I/O ports and Serial Ports

I/O Ports or Input / Output Ports enable the microcontroller, connection to the outside components. Input Ports give a gateway for passing on the data from the outside components .

The data from the input ports is modified and will determine the data on the output port.

Output Ports allows microcontroller to control external devices (like motor components and LEDs). Generally, all ports in microcontrollers have dual functionality means they can act as both input and output port.

Clock Generator (Oscillator)

A clock signal controls the operations inside the microcontroller and other parts to be synchronous to each other . A Clock Generator is an very important part of the Microcontroller’s Architecture and the user has to provide an additional Timing Circuit in the form of a Crystal.

8051 MicroController

First we see the block diagram of 8051 micro controller.

The above diagram illustrates the block digram of 8051 micro controller.

Feature of 8051

  • It has 8 bit CPU with 2 registers A and B.
  • Internal ROM of 8K Bytes – 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.
  • 32 I/O Pins (Input / Output 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 / Counters – T0 and T1.
  • Control Registers – SCON, PCON, TCON, TMOD, IP and IE.
  • Serial Data Transmitter and Receiver for Full – Duplex Operation – SBUF.
  • Interrupts: Two External and Three Internal.
  • Oscillator and Clock Circuit. 

These are some feature of 8051 micro controller.

The pin digram:

The pin description is given Below:

  • Pins 1 to 8 − These pins are known as Port 1. This port doesn’t serve any other functions. It is internally pulled up, bi-directional I/O port.
  • Pin 9 − It is a RESET pin, which is used to reset the microcontroller to its initial values.
  • Pins 10 to 17 − These pins are known as Port 3. This port serves some functions like interrupts, timer input, control signals, serial communication signals RxD and TxD, etc.
  • Pins 18 & 19 − These pins are used for interfacing an external crystal to get the system clock.
  • Pin 20 − This pin provides the power supply to the circuit.
  • Pins 21 to 28 − These pins are known as Port 2. It serves as I/O port. Higher order address bus signals are also multiplexed using this port.
  • Pin 29 − This is PSEN pin which stands for Program Store Enable. It is used to read a signal from the external program memory.
  • Pin 30 − This is EA pin which stands for External Access input. It is used to enable/disable the external memory interfacing.
  • Pin 31 − This is ALE pin which stands for Address Latch Enable. It is used to demultiplex the address-data signal of port.
  • Pins 32 to 39 − These pins are known as Port 0. It serves as I/O port. Lower order address and data bus signals are multiplexed using this port.
  • Pin 40 − This pin is used to provide power supply to the circuit.

In this , 8051 block digram and pin descriptions are discussed .for more information please click here.

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