CPU in Microcontroller

Central processing unit (CPU) is the brain of a microcontroller. CPU is responsible for finding and fetching the right instruction which needs to be executed, for decoding that instruction, and finally for its execution.

Central processing unit connects all parts of the microcontroller in one systems. CPU most important function is to decode program instructions. When programmer writes a program, instructions have a clear form like MOVWF PORTB. However, in order for a microcontroller to understand that, this 'letter' form of an instruction must be translated into a series of zeros and ones which is called an 'opcode'. This translation from a letter to binary form is done by translators such as assembler translator or also known as an assembler.

Instruction fetched from program memory must be decoded by a central processing unit (CPU). We can then select from the table of all the instructions a set of actions which execute a assigned task defined by instruction. As instructions may within themselves contain assignments which require different transfers of data from one memory into another, from memory onto ports, or some other calculations, CPU must be connected with all parts of the microcontroller. This is made possible through a data bus and an address bus.

Microcontroller Vs Microprocessor

Microprocessor and microcontroller are two pupolar terms in world of computer. However,microprocessor and microcontroller has different functions and features.

Microprocessors generally require external components or circuits to implement program memory, RAM memory and Input/Output. Intel's 8085, 80386 and Pentium are examples of microprocessors. Microcontrollers incorporate program memory, RAM memory and input/output port into one chip. Microchip's PIC series and Atmel's AVR series are examples of microcontrollers.

One of the main differences is that microcontrollers are usually designed to perform a small set of specific functions, for example as in the case of a Automatic Braking System which performs a small set of input processing functions, whereas microprocessors tend to be designed to perform a wider set of general purpose functions. For example, microcontrollers are widely used in modern cars where they will each perform a dedicated task, i.e. a microcontroller to regulate the brakes on all four wheels, or a microcontroller to regulate the car air conditioning, or a microcontroller for automatic gate systems.

These microcontrollers will perform few other tasks (if any) other than those specified. Compare to a microprocessor in a PC which performs a wide range of tasks related to the general requirements of a PC such as performing the necessary calculations for a very wide set of software applications, performing Input/Output for the main subsystems, peripheral control and etc.