Today we are living in the world of computers. Computers have invaded all sectors of society. We use computers at home, at offices, for our day to day activities. The brain of the computer is the CPU (Central Processing Unit), which is built using a micro processor or several microprocessors depending upon the complexity of the computing system. The microprocessor is a programmable logic device that can be used to do a variety of tasks ranging from a very simple to a very complicated one. Today we have embedded systems designed to perform a one and only one task. The brain of an embedded system is a micro controller.