New microprocessors, memory devices, interface chips, and other exotic microcomputer components enter the market every year, and it is popular to talk about these fad items. Magazine article after magazine article and even whole books are devoted to the popular devices.
Two important areas of microcomputer systems that are usually over-looked are the control structure of microprocessors and the input and output methods used to get data in and out of the closed microcomputer – memory systems. A new microprocessors, such as the Intel8086, is usually described as revolutionary processor with so many index register, so many data registers and a “pipelined” architecture. Little, if anything, is ever said about microprocessor’s micro programmed control point instruction-execution logic, or the internal workings of the priority arbitration logic. Most manufacturers’ and authors’ block diagrams of microprocessors, in fact, pass off the most sophisticated part of the processor-the timing and control unit-as a simple box with the words “timing and control logic” writ-ten inside.