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CHAPTER 2

MICROCOMPUTER

ARCHITECTURE

Before we begin to discuss assembly language, we should take time to

explore the world of the microcomputer. Just what is a microcomputer?

As the name implies, it is a small computer. This should not mislead you

into thinking that a microcomputer cannot be a powerful computing tool.

In fact, the microcomputers of today are as powerful as the minicomput

ers and mainframe computers of just a few years ago. The reduction in

size has been a direct consequence of the development of integrated cir

cuits (chips) that contain the functional equivalent of many thousands of

transistors.

A microprocessor is an integrated circuit that is the basic functional

building block of the microcomputer. Figure 2 shows the organization

of a basic microcomputer system. The central processing unit (CPU) is

the microprocessor chip itself. Electrically connected to the CPU chip is

memory. Memory can be of various sizes—for example, over 16 million

bytes for the 68000 microprocessor. Also connected to the CPU are input

and output (I/O) devices that allow the CPU to communicate with the

outside world through a terminal, as well as other information storage

devices such as floppy disks and magnetic tapes.

The Motorola M68000 Family

The M68000 family of microprocessors is the current step in a

continually evolving microprocessor technology. The M68000 family

consists of a number of different CPU chips. Among these are the MC68000,

MC68008, MC68010, and the MC68020, and the very new MC68030 (actual

chips are designated with the prefix MC). Later on in this book I will

refer to the M68000 family or the MC68000 CPU chip as just the 68000.

Motorola, like the other major microprocessor designers, didn’t start

with a chip as sophisticated as the MC68000. Prior to the introduction of

the M68000 family, Motorola’s bread-and-butter microprocessor line was

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Motorola M68000 Guida Utente Pagina 31