A Microprocessor is a programmable electronic device that has computing and decision making capability similar to that of a central processing unit (CPU) of a computer. Today, the applications of the microprocessor are increasing at a faster rate. Microprocessor can be embedded in a large system or it can be a stand alone unit capable of controlling different processes. It can also function as CPU of a computer. At a very elementary level, we can draw an analogy between microprocessor operations and functions of a human brain. The brain gets inputs from eyes, ears etc (input devices) and sends processed information to "output devices" such as face in the form of expressions and emotions. Generally a microprocessor is a programmable device, which accepts binary data from an input device, process the data according to the instructions stored in the memory, and provides the result to an output device. Prior to going into the details of a microprocessor, we must have a basic knowledge of computers.

Basic elements of a computer

All computer systems consist of three basic functional blocks as shown in figure.

(1) Central Processing Unit (CPU)

(2) Memory

(3) Input and Output devices

A system designed with a microprocessor as its central processing unit is called a microcomputer. A microprocessor based system includes a microprocessor as CPU, semiconductor memories, input and output devices, interfacing devices and so on. The organization of a microcomputer (microprocessor based system) is shown in Figure. These functional blocks are linked together with three internal buses. Bus is a communication path between the CPU and peripherals (devices) with a group of wires to carry bits.

The three buses are the data bus, the address bus and the control bus. The input and output devices are connected to the input and output ports respectively. A port is a physical interface on a computer through which data are passed to and from the peripherals. An instruction is a command given to the computer to perform a given task. A group of instructions designed to solve a specific problem is called a program. These instructions and data are stored in specific locations in the memory. Each location has a unique address associated with it.

Instructions are obtained by the CPU by placing the address (of the memory location where instruction is stored) in the address bus. Now the instructions are transferred to the CPU through the data bus. The CPU executes these instructions sequentially to get the final result. The processed data (result) is stored back in the memory or sent to peripheral devices like monitor, connected to the computer. All these processes are controlled and coordinated by the signals on the control bus generated by the CPU.

MICROPROCESSOR

As stated earlier, microprocessor can function as CPU of a computer. It includes all logic circuitry necessary for performing various operations specific to that processor. For the sake of clarity, the microprocessor can be divided into three segments.

(a) Arithmetic and logic unit (ALU)

(b) Registers

(c) Control Unit.

ALU

This is the area of the microprocessor where various computing functions are performed. The ALU performs arithmetic operations like addition and subtraction, and logical operations like AND, OR and NOT. We can consider ALU as a section of CPU which contains all the logic circuits needed for performing different operations specific to that processor. A particular instruction (i.e., machine code of a particular instruction) will activate the appropriate logic circuit in the ALU so that a particular task is performed. This is called microprogramming which is done in the design stage of the microprocessor. We can compare the operation of microprocessor with the operation of our brain. In early childhood, we learn a word "sit" and the physical motion needed for the action "sit" are embedded in our brain. Later, when we hear the word "sit", our brain activates a series of actions for our muscles and bones, so that we perform the action "sit". In this analogy, the word "sit" is like an instruction to the microprocessor and action initiated by the brain are like microprogram.

The bit pattern (machine code of instruction) required to initiate these microprograms are given to the programmer in the form of instruction set of the microprocessor. The programmer selects the appropriate bit pattern (instruction) from the instruction set, for a given task and enters them sequentially to the memory through an input device. When CPU reads these bit patterns (instruction) one at a time, it initiates the appropriate microprogram through the control unit and performs the task specified in the instruction.

Registers

We can consider registers as temporary memory locations seen inside the processor. These registers are identified by the letters A, B, C, D, E, H, and L.

Control Unit

The control unit provides the necessary control signals for all the operations in the processor. It controls the flow of data between the microprocessor, the memory and the peripheral devices like keyboard and monitor.

Advantages of Microprocessor based systems

(i) Processing speed is high.

(ii) Automation of industrial processes and office administration.

(iii) Since the device is programmable, there is flexibility to alter the system by changing the software alone.

(iv) Compact and low cost.

(v) It is more reliable.

(vi) Operations and maintenance are easier.

Applications of Microprocessor based systems

Microprocessors are widely used in control applications.

(i) Microprocessor based systems are widely used in frequency meters, frequency synthesizers, spectrum analyzers etc.

(ii) In industry, they are widely used for controlling various parameters like speed, temperature and pressure.

(iii) In telephone industry they are widely used in digital telephone sets, telephone exchange and modems.

(iv) They are used in automobiles for monitoring various quantities like air-fuel mixture, temperature, speed etc.

(v) 32-bit microprocessors are widely used in CAD machines.

(vi) The car, maruti wagonR also uses a 32 bit processor for controlling the MPFI unit.