From ArticleWorld

A microcontroller is a digital electronic device consisting of a processor along with other special functional components. These include random access memory (RAM), read - only memory (ROM), timers, and serial communication and input/output capabilities all integrated onto a single chip. It has the advantage that external devices are not required to make it perform specialized functions.

Main features of microcontrollers

Microcontrollers consist of four basic functional blocks:

  1. The main central processing unit (CPU).
  2. Memory for the monitor program which is stored on the read-only memory (ROM) or the flash memory.
  3. Timers/counters.
  4. Input/output lines to interface with external peripheral components.

Apart from the above, a clock generator is also present inside the microcontroller. The clock generator depends on an external timing crystal and some special software instructions to make it work. Software control is also done for monitoring serial communication using standards like I2C. A serial port is provided for the purpose.

The main difference between a microcontroller and a desktop computer is that no communication is done by the former with input/output devices. User involvement is limited and tasks are carried out automatically.


Often referred to as ‘computers on chips’, microcontrollers need to be programmed appropriately to carry out specific tasks. The vast majority of electronic goods have microcontrollers in them. In the household, for instance, washing machines, telephones and microwave ovens have microcontrollers. Communication gadgets like pagers and mobile phones also have these embedded controllers. Automobiles, televisions, video cassette recorders (VCRs) and video games are equipped with microcontrollers.

Most of these devices are ‘simple’ controllers, while the more complicated digital signal processors (DSPs) are used in advanced telecommunication systems.


It was in the 1970s that the ‘computer-on-a-chip’ concept began to gain importance. Texas Instruments developed the 4-bit TMS 1000 and came up with a version for driving a calculator. Intel’s 4004 too was suited for a calculator.

The 8051 microcontroller was developed in 1981 by Intel. It had an 8-bit data bus, 128 bytes of RAM, 4 KB of on-chip ROM, two timers, a serial port and four input/output ports each 8 bits wide. It was the first in the so-called MCS-51 family. Different manufacturers now produce versions of the 8051 with varying speeds and amounts of on-chip ROM available. The instruction sets, however, are compatible with the original version.

Memory is provided in various forms in microcontrollers. The UV-EPROM version (8751), consisting of erasable programmable memory using ultra-violet rays, and the ‘non-volatile RAM’ version called the NV-RAM (Dallas Semiconductor’s DS5000) are two examples. The flash memory version of the 8051 made by Atmel Corporation is known as the AT89C51. In this device, no separate ROM eraser is required. The PROM burner is sufficient for writing into the memory; the memory can be done away with in a ‘flash’.

One-time programmable (OTP) versions of the flash and NV-RAM microcontrollers are also available. A new development in the manufacture of microcontrollers is the introduction of the Philips version of the 8051 series. The new devices have features such as analogue-to-digital converters, digital-to-analogue converters and extended input/output capabilities. They are available in both the OTP and flash memory forms.