What is a Microcontroller?

Block Diagram of a Single Chip Computer

A small computer usually implemented on a single Integrated Circuit (IC) that contains a central processing unit (CPU), some memory, and peripheral devices such as counter/timers, analog-to-digital converters, serial communication hardware, etc.

Microcontrollers are used in automatically controlled products and devices and other embedded systems. By reducing the size and cost compared to a design that uses a separate microprocessor, memory, and input/output devices, microcontrollers make it economical to digitally control even more devices and processes.

Microcontrollers are embedded inside another device so that they can control the features or actions of the product.
Microcontrollers are dedicated to one task and run one specific program. The program is stored in ROM (read-only memory) and generally does not change.
Microcontrollers are often low-power devices.
A microcontroller has a dedicated input device and often (but not always) has a small display for output. A microcontroller also takes input from the device it is controlling and controls the device by sending signals to different components in the device.

Internal Structure of a Typical Microcontroller

Microcontroller Architectures

In a microprocessor, input /output (I/O) devices are externally interfaced and are mapped either to memory address (memory mapped I/O) or a separate I/O address space (I/O mapped I/O). There are two possible architectures one is Princeton (Von Neumann) and another is Harvard.

I/O Registers space in Princeton architecture have only one memory interface for program memory (ROM) and data memory (RAM). One option is to map the I/O Register as a part of data memory or variable RAM area ( memory mapped I/O). Alternatively a separate I/O register space can be assigned (I/O Mapped I/O). The Princeton or Vonneumann architecture one bus is used to carry the address and data with an appropriate multiplexing technique, which in turn reduces the cost. But Harvard architecture has separate Data memory and separate Code or Program memory. Since there are separate bus for access the operation of fetching the code and data can happen simultaneously which increases the speed of operation of execution inside CPU.