01 Concepts and Fundamentals

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Microcontrollers

Concepts and Fundamentals


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Microcontrollers 2

Objectives

To know and understand the concepts andfundamentals related to the study of microcontrollers


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Microcontrollers 3

Contents

Review of a microcomputer system

Central processing unit, CPU

CPU cycles

Definition of buses PIC microcontroller architecture


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Microcontrollers 4

A Typical Microcomputer System


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Microcontrollers 5

A Typical Microcomputer System

The operation of the whole system is under control of aCentral Processing Unit (CPU)

There is support for bidirectional human interface (I/O)

I/O ports for interaction with the outside world(peripheral)

Primary memory for program and data

Secondary memory for mass storage and data backup

Auxiliary memory for graphics processing


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Microcontrollers 6

Central Processing Unit (CPU)

IR

INSTRUCTION

DECODER

ALU

PROGRAM

+

PC

R0-R15

17

OEN

8

WRITE

LD_IR

LD_IR_LSN

SEL_DATA_RAM1

JUMP_PC INC_PC

C

Z

ACC

AOP

1111111111111

0000000000

CEN

WEN

4

4

4

4

7

7

8

4

7

7


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CPU Cycles

The operation of a typical CPU can be decomposed intothree main cycles: fetch, decode and execute

The fetch cycle consists in getting an instruction from

the instruction memory and storing it in the instructionregister

The decode cycle consists in translating the bit pattern

of the instruction into control signals (instruction

decoder) The execute cycle consists in inputting data to the ALU,

selection an ALU operation and storing the result in

either an internal register or the data memory



Buses

Three buses can be found in a microcomputer system:data, control and address bus

The data bus is the communication channel between the CPU

and the rest of the system

The address bus allows the selection of the

source/destination of the data

The control bus determines the type of communication that

takes place, i.e. reading or writing access



Buses

A schematic diagram indicating the communication ofthe three buses with the CPU is shown below



Microprocessors vs. Microcontrollers

Microcontroller-based systems are microcomputersystem built around a microprocessor (CPU) and a set

of memories and peripherals, all encapsulated in an

integrated circuit (IC)


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Microcontrollers 11

Microprocessors vs. Microcontrollers

Regarding applications Microprocessors are used in data-processing applications

Microcontrollers are used as reactive systems that deal with

events from the outside world and as control systems with I/O

interfacing

Regarding the instruction set

Microprocessors support complex addressing modes that are

aimed to handling several structures of data: arrays, pointers,

etc.

Microcontrollers are aimed to controlling and monitoring I/O

ports in terms of verification of status bits, interrupts and

timers


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Von Neumann Architecture

A single integrated circuit memory that holds data andprogram

The CPU is in charge of identifying data from program

Same bits width for data and instructions

CPUCPU

DATADATA

andand

PROGRAMPROGRAM

MEMORYMEMORY


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Microcontrollers 14

Harvard Architecture

Data and program have their own memory

The bit widths may differ

Simultaneous access are allowed

CPUCPUDATADATA

MEMORYMEMORY

(RAM)(RAM)

PROGRAMPROGRAM

MEMORYMEMORY

(ROM)(ROM)


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Microcontrollers 15

Pipeline Processing

The internal architecture is divided into independentblocks that are serially connected forming a pipeline

The execution of an instruction is allocated to a certain

number of blocks Execution of several instructions can be simultaneously

executed in an one-after-the-other fashion

BLOCKBLOCK

11

BLOCKBLOCK

22

BLOCKBLOCK

33

BLOCKBLOCK

44


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Microcontrollers 16

RISC, CISC ans SISC Processors

CISC (Complex Instruction Set Computer) Large number of instructions

Complex and powerful instructions

RISC (Reduced Instruction Set Computer) Reduced number of instructions

Simple instructions ans easy coding

SISC (Specific Instruction Set Computer)

Reduced number of instructions

Application-oriented instructions


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Microcontrollers 17

Orthogonal Architecture

In a traditional architecture, the outcome of an ALUoperation can only be stored in the accumulator

In an orthogonal architecture, the outcome of an ALU

operation can be stored in an internal register as well asthe accumulator

ALUALU

DATADATA

MEMORYMEMORY

ACCACC

ALUALU

DATADATA

MEMORYMEMORYWW

Traditional

Orthogonal


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Summary

Microcontrollers are microcomputer systems made up ofa CPU, memories and peripherals presented as an IC

The execution of instructions by the CPU has three

phases: fetch, decode and execute Microchips PIC have a harvard, RISC and orthogonal

architecture

The microcontrollers that will be studied are 8-bit data

wide

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01 Concepts and Fundamentals