Central processor unit operation

At the heart of a microcomputer system lies the Central Processor Unit (CPU) or processor. The processor runs a program by repeatedly fetching and executing instructions from main memory. By using a step-by-step approach, this chapter outlines the way in which this is done using a highly simplified processor. This will provide a foundation for understanding the operation of a real processor in Chapter 5. This chapter and Chapter 5 deal with the principles of machine code and assembly language programming. Machine code is the native code of the processor while assembly language is a more programmer friendly language that is translated into machine code by a program called an assembler. The full treatment of machine code and assembly language programming are found in other texts, some of which are listed in the references at the end of the book. The purpose of this chapter and the next is to explain and demonstrate how the components of a processor work together to carry out tasks.