(Delmar) Technician's Guide to 68HC11 Microcontroller.pdf

chapter

Introduction to Computer Hardware

Objectives

I ntrodu ct ion to Com put er H ardware

After completing this chapter, you should be able to:

Describe the fundamental elements of every computer system: proces-

sor, memory, and input/output

◗

Compare elements of the HC11 block diagram to the fundamentals of

every computer system

◗

Describe the use of busses to connect computer elements

◗

Explain the three major functional units of a processor

◗

Illustrate the typical registers inside the processor

List the HC11 processor registers

◗

Discuss the HC11 processor modes

◗

Compare and contrast various memory types

◗

Describe the on-chip memory of the HC11

Specify input/output functions present on most computers

◗

Use some basic BUFFALO commands to control the EVBU

◗

Outline

◗

1.1 Elements of Every Computer

◗

1.2 Elements of Processors

1.3 Introduction to Memory

◗

1.4 Memory Types

◗

1.5 Input/Output

◗

1.6 EVBU/BUFFALO

◗

Technician’s Guide to the 68HC11 Microcontroller

Introduction

Computer systems have been developed for a variety of functions and purposes.

General-application desktop machines are the most common. They run a variety of

software applications, such as word processing, financial management and data

processing. They have all but replaced the typewriter as a necessary business tool.

Computers are also present in automobiles, appliances, airplanes and all types of

controllers and electromechanical devices.

Despite the differences among these computer systems, they all share fundamental

components and design. The purpose of this chapter is to provide an understanding

of the fundamental components of a computer system. A conceptual presentation

regarding the elements of every computer system is made with sufficient detail to

establish a foundation for these concepts. The concepts will then be extended to the

HC11 hardware.

1.1 Elements of Every Computer

All computers are made up of a group of three fundamental elements: a central

processor, memory, and input/output devices. Figure 1.1 shows a block diagram of a

computer that includes these three elements. The examination of any kind of desktop

computer, workstation or computer control system will reveal at least this minimum

structure. Many computing devices will have multiple processors, multiple memory

types, and numerous input/output devices. In many cases, the input/output devices

contain all three elements as a unit. Video cards for personal computers, for example,

always contain a video processor and memory in addition to their inherent input/out-

put capability.

Address Bus

Memory

Data Bus

Central

Processor

(CPU)

Connection to the

Outside World

Input/Output

Control Bus

Figure 1.1

Fundamental Block Diagram of a Computer

Introduction to Computer Hardware

HC11 Hardware Block Diagram

The HC11 is a computer system on a single chip that contains the three functional

blocks of a computer system. Its internal central processor is a member of the 6800

family of processors; it has on-board memory and sophisticated on-chip input/output

capabilities.

The HC11 block diagram is shown in Figure 1.2. This block diagram is specific to the

M68HC11E9 version of the HC11. This version of the HC11 is used on the development

board (EVBU), as well as in the examples used throughout this text. Three types of

memory are included on-chip: RAM, ROM and EEPROM. The HC11 also supports

expanded off-chip memory. It contains five on-chip input/output functions, an

analog-to-digital converter, and a sophisticated timing system that supports numerous

event-driven functions. The address, data and control busses are not shown in this

diagram; the processor is connected to the memory and input/output functions inside

the HC11 chip in the manner illustrated in Figure 1.1.

Figure 1.2

M68HC11E9 Block Diagram

Technician’s Guide to the 68HC11 Microcontroller

NOTE: Throughout this text, references to the HC11 presume the M68HC11E9

version of the chip; thus, the shorter, more general name “HC11” will be used,

unless otherwise specified.

Central Processor

The processor is the device at the center of the machine. It has the responsibility to

execute instructions, manipulate data and perform arithmetic functions. It controls

and manages the activities of the entire machine. The human brain is the ultimate

processor. It can receive and process instructions, process data (like visual images and

sounds) and perform arithmetic calculations. However, the human brain is much,

much more than a processor because it has the ability to think and to reason. Computer

processors cannot think in the same sense.

The term Central Processing Unit (CPU) is used to refer to the main processor in a

system. The CPU often works in conjunction with a set of processors to complete a

whole system. Modern computers contain additional processors, other than the CPU.

They contain video processors, input/output processors, memory controllers, interrupt

controllers and math co-processors, to name a few. Since these other processors are

subordinate to the central processor, they are often called sub-processors . Many

peripheral devices, such as harddrives, printers and video projection systems, have

dedicated processors embedded into their control circuitry.

Memory

Memory is a term that refers to any component that stores data and programs used by

the processor. Memory can have many forms. There are semiconductor memories,

magnetic memories, and optical memories. Semiconductor memories include read

only memory (ROM) and read/write memory (RAM). Magnetic memories include

floppy disk drives, hard disk drives and tape systems. Optical memories include

CD-ROM, DVD and optical disks. A thorough presentation of memory relevant to the

HC11 will be provided in chapter 8. Section 1.3 will address concepts of memory that

are applicable to all computer systems and a necessary foundation for this study of the

HC11.

Input/Output

Input/Output is a term that refers to any subsystem that has the responsibility of

receiving data for the processor (input) or sending data out from the processor

(output). Input/Output is typically abbreviated as I/O and does not necessarily imply

that a particular device has both input and output capability. Typical input devices are

keyboards, mice or scanners. Typical output devices are printers and monitors. Typical

devices that perform both input and output functions are modems or tape drives.

Collectively, all these devices are referred to as I/O devices. The HC11 I/O capability

is discussed in detail in chapters 10 through 13.

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