8051 Microcontroller

8051 microcontroller is an 8-bit microcontroller created in 1981 by Intel Corporation. It has an 8-bit processor that simply means that it operates on 8-bit data at a time. It is among the most popular and commonly used microcontroller.

As it is an 8-bit microcontroller thus has 8-bit data bus, 16-bit address bus. Along with that, it holds 4 KB ROM with 128 bytes RAM. We will discuss the complete architecture of 8051 microcontrollers. But before that, see the contents under this article.

Content: 8051 Microcontroller

    1. What is Microcontroller
    2. Architecture
    3. Characteristics
    4. Applications

What a Microcontroller is?

A microcontroller is an integrated chip designed under Very Large Scale Integration technique that consists of a processor with other peripheral units like memory, I/O port, timer, decoder, ADC etc. A microcontroller is basically designed in such a way that all the working peripherals are embedded in a single chip with the processor.

Any programmable device holds a processor, memory, I/O ports and timer within it. But a microcontroller contains all these components embedded in a single chip. This single-chip manages the overall operation of the device.

We have already discussed microprocessors in our previous article. A microprocessor simply contains a CPU that processes the operations with the help of other peripheral units. Microprocessors are used where huge space is present to inbuilt a large motherboard like in PCs.

However, microcontrollers are used where programming is to be performed on the smallest tiny space present. A microcontroller holds separate memory locations for both data and program.

Let us now have a detailed idea about 8051 microcontrollers.

Architecture of 8051 Microcontroller

The figure below represents the architectural block diagram of 8051 microcontroller:

architecture of 8051 microcontrollerAs we can see that several units are present in the above architecture. And every unit is embedded to execute the desired operation. Let us now discuss the operation of each unit present in the architecture.

1. Central processing unit (CPU): 8051 uses the 8-bit processor. This unit carries out the operation on 8-bit data. A processor is the heart of microcontroller. As the execution of the program stored in the memory is performed by the processor.

The unit performs arithmetic and logical operations on 8-bit data as it has ALU, with internal registers and program counters.

Several logical operations are performed by the ALU according to the program stored in the memory.

The processor of 8051 microcontrollers possesses a special feature by which it can process single bit or 8-bit data. This simply means that it has the ability to access each single bit data either to clear, set or move etc. for any logical computation.

2. Memory: Basically 8051 microcontroller consists of on-chip program memory i.e., ROM and on-chip data memory i.e., RAM.

Let us first understand

  • ROM
    8051 microcontroller has 4 KB ROM with 0000H to 0FFFH as the addressable space. It is completely a program or code memory that means used by the programmer to store the programs that are to be executed by the microcontroller.
    The operations that are executed by the device in which the microcontroller is present are stored in the ROM of the memory at the time of fabrication. Hence cannot be changed or modified.
  • RAM
    8051 holds a 128 bytes RAM. Basically, RAM is used to store data or operands for only a small time duration. It can be altered anytime according to the need of the user. It is also known as the data memory as it stores the data temporarily.
    Out of the 128-byte RAM, first, 32 bytes is held by the working registers. Basically, these are 4 banks which separately has 8 registers. These registers are accessed either by its name or address. It is to be noted here that at a particular time only a single register bank can be used.
    As in 8051, the data and program memory i.e., RAM and ROM hold a definite memory space. However, for some applications there exist the need for external memory to enhance the memory space, thus external RAM, ROM/EPROM is used by the 8051 microcontrollers.

3. 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.

4. Timer and Control Unit: Timers are used to create a time gap or delay between 2 events. 8051 microcontroller consists of 2 timers of 16 bit each by which the system can produce two delays simultaneously in order to generate the appropriate delay.

Basically, microcontrollers use hardware delays in which a physical device is used by the processor to produce the respective delay. And this physical device is known as a timer.

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.

Though the processor can also generate a delay according to the need of the system. But this will lead to keep the processor busy all the time as it will not do any other operation in that particular time duration. So, the presence of timer in the microcontroller, allows the processor to be free in order to execute other operations.

Along with these units, the microcontroller chip also includes data pointer, program counter, stack and stack pointer, temporary registers, instruction registers with latches and buffers for the I/O ports.

Characteristics of 8051 Microcontroller

  1. An 8-bit processor.
  2. Data memory or RAM of 128 bytes.
  3. Program memory or ROM of 4 KB.
  4. 2 timers of 16 bit each.
  5. 8-bit data bus.
  6. 16-bit address bus.
  7. Offers bit addressable format.
  8. Special function registers and serial port.
  9. 32 input/output lines.

Applications of 8051 Microcontrollers

Microcontrollers find its various applications like in electronic gadgets (like keyboard, mouse etc), automobiles, e-commerce, electronic household items (like ovens, washing machines) etc.

So, this is all about the basic architecture and characteristics of 8051 microcontrollers.

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