8051 Microcontroller

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Introduction to 8051

What is a Microcontroller ?

A microcontroller is a small computer on a single IC (Integrated Circuit). That is, MCU stands for microcontroller unit and UC for μ-controller IC. This consists of all kind of electronic components for doing each and every task using with this.

8051 microcontroller

The 8051 is the first microcontroller of Intel Corporation and the IC family is MCS-51, was developed in 1980. This microcontroller was developed using N-type Metal Oxide Semiconductor (NMOS) technology and later it known as CMOS after developing 80C51 series of microcontrollers. CMOS stands for, Complementary Metal Oxide Semiconductor (CMOS) technology. As comparing to NMOS, CMOS’s power consumption was much lesser than NMOS types. And it can be used in better compatible for battery powered applications.
Based on the bit processing capability, the microcontrollers can be classified. For example; an 8-bit microcontroller means it can read, write and process 8-bit data. Basically it specifies the size of data bus.
Nowadays microcontrollers are designed with much more compact, cheap and powerful specifications like AVR (Advanced Virtual RISC) and PIC (Peripheral Interface Controller).

General Purpose Microprocessor System

Microprocessors need external devices such as:

1. ROM (for program storage functions)
2. RAM (for data storage purposes)
3. 8253 (for timer systems)
4. PPI 8255 (for I/O port operations)
5. USART (for serial communication methods)

All the above mentioned peripheral are integrated together to form controlling unit ready to embed within the applications.

General Purpose Microcontroller System

the microcontroller has all memories and ports available on a single chip. This feature makes microcontrollers most popular in electronic industry. After the generation of these Intel powered microcontrollers, many semiconductor companies developed their own microcontrollers with different specifications.

8051 Architecture

8051 Architecture

ROM (Read Only Memory)

1. 4KB ROM is available for program storage.
2. It is Non-Volatile type of memory. It means that data is not lost even in the event of power turned OFF.
3. This microcontroller has 16-bit address. It means it can access 2^16 memory locations and we can interface up to 64 KB of program memory externally in case of large applications.

RAM (Random-access memory)

1. It has128-byte RAM for data storage.
2. It is Volatile type of memory. It means the data will lost when power for the device is turned OFF.
3. Used during the execution time to store data temporarily.
4. RAM consists of register bank, stack and temporary data storage with some SFR’s (Special Function Registers).


8051 microcontroller has inbuilt central processing unit which is also called as ALU (Arithmetic Logic Unit) which performs all arithmetic and logical operation.

8051 Pin diagram & Discription

8051 pin diagram

Timers and Counters

1. It has two timer pins T0 and T1.
2. Using these timers we can generate delay time for various tasks.
3. It can count external pulses or events in counter mode
4. There are two 16-bit timer registers are available as T0 (TH0 & TL0) and T1 (TH1 & TL1).
5. TMOD register used to select mode and TCON register used to select mode, and control their timer operation.


1. Interrupts are requested by internal or external peripherals. Which are masked while not in use.
2. Interrupt handler process are called after each interrupt event occurs.
3. These processes are called as Interrupt Service Routine (ISR) and are located in special memory loc.
4. To accept external interrupts, pins INT0 and INT1 are used.

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