Page 74 - DCAP210_INTRODUCTION__TO_MICROPROCESSORS

Introduction to Microprocessors

Notes Objectives

After studying this unit, you will able to understand the following:
• Describe Microcontroller Systems (Microcomputer System)

• Understand Microcontroller Architectures
• Explain Microcontroller Features
• Example of Microcomputer
• Define I/O Devices of Microcomputer System

Introduction

The term microcomputer is used to describe a system that includes a minimum of a microprocessor,
program memory, data memory, and input/output (I/O). Some microcomputer systems include
additional components such as timers, counters, analogue-to-digital converters and so on. Thus,
a microcomputer system can be anything from a large computer having hard disks, floppy disks
and printers to a single chip computer system.
5.1 Microcontroller Systems (Microcomputer System)

The microcomputers consist of single silicon chip. Such microcomputer systems are also called
microcontrollers.
Microcontrollers are general purpose microprocessors which have additional parts that allow
them to control external devices. Basically, a microcontroller executes a user program which is
loaded in its program memory. Under the control of this program data is received from external
devices (inputs), manipulated and then sent to external output devices. A microcontroller is a
very powerful tool that allows a designer to create sophisticated input/output data manipulation.
Microcontrollers are classified by the number of bits in a data word. 8-bit microcontrollers are the
most popular ones and are used in many applications. 16- and 32-bit microcontrollers are much
more powerful, but usually more expensive and not required in many small to medium general
purpose applications where microcontrollers are used.
The simplest microcontroller architecture consists of a microprocessor, memory, and input/output.
The microprocessor consists of a central processing unit (CPU) and the control unit (CU).
The CPU is the brain of a microprocessor and is where all of the arithmetic and logical operations
are performed. The control unit controls the internal operations of the microprocessor and sends
out control signals to other parts of the micro-processor to carry out the required instructions.

How to differentiate between ROM and RAM?

5.2 Microcontroller Architectures

Basically, two types of architectures are used in microcontrollers: Von Neumann architecture
and Harvard architecture. Von Neumann architecture is used by a very large percentage of
microcontrollers and here all memory space is on the same bus, and instruction and data are
treated identically. In the Harvard architecture (used by the PIC microcontrollers), code and data
storage are on separate buses and this allows code and data to be fetched simultaneously, resulting
in a more efficient implementation.
5.2.1 RISC and CISC

RISC (Reduced Instruction Set Computer) and CISC (Complex Instruction Set Computer) refer to
the instruction set of a microcontroller. In a RISC microcontroller, instruction words are more

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