Microprocessor Theory and Applications with 68000/68020 and Pentium

2

MICROCOMPUTER ARCHITECTURE

In this chapter we describe the fundamental material needed to understand the basic characteristics of microprocessors. It includes topics such as typical microcomputer architecture, timing signals and internal microprocessor organization, and status flags. The architectural features are then compared to the Intel Pentium. Finally, an overview of pipelining, superscalar microprocessors, RISC vs. CISC, and the branch prediction feature is included.

2.1 Basic Blocks of a Microcomputer

A microcomputer has three basic blocks: a central processing unit (CPU), a memory unit, and an input/output (I/O) unit. The CPU executes all the instructions and performs arithmetic and logic operations on data. The CPU of the microcomputer is called the microprocessor typically a single VLSI (very large scale integration) chip that contains all the registers and control unit, and arithmetic-logic circuits of the microcomputer.

A memory unit stores both data and instructions. The memory section typically contains ROM and RAM chips. The ROM can only be read and is nonvolatile; that is, it retains its contents when the power is turned off. A ROM is typically used to store instructions and data that do not change. For example, it might store a table of seven-segment codes for outputting data to a display external to the microcomputer for turning on a digit from 0 through 9.

One can read from and write into a RAM. The RAM is volatile; that is, it does not retain its contents ...