Microelectronics - Systems and Devices

Part B – The Software

7	Instructions

Summary

The CPU reads a program in a series of fetch-execute cycles in which it reads a machine code instruction and then obeys it. Writing programs in machine code is difficult, but easier if we use an assembler program and write it in mnemonics. The assembler turns the mnemonics into machine code. A program written in assembler can have a title and comments added to it, to make it even easier to understand.

A CPU can do many different things, but it does nothing unless it is told to. It needs to be issued with instructions. The instructions are issued to it in the form of a program, stored in memory. The instructions that a given CPU can understand and obey are its instruction set.

Different types ...