Intoduction to Microcontrollers - PIC

7/22/2019 Intoduction to Microcontrollers - PIC

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Introduction to Microcontrollers

By Mr Gregory. K. Mavhunga


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Outline

What is a microcontroller

Why we use microcontrollers

PIC microcontrollers Architecture

Programming a PIC [16F628A]

Example application

Summary


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Microcontroller samples


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What is a microcontroller

A microcontroller is a stand alone, self

contained system with peripherals,

memory, and a processor.

Unlike microprocessor systems, which

typically have RAM, ROM and other

peripheral devices as standalone ICs or

modules

Contains all these items on one IC


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Advantages of microcontrollers

Ease of use and accessibility

Low cost with optimal performance

Low power requirements, typical ofembedded devices

Easily replaceable or re-purposed/ re-

programmed


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Typical components of microcontroller

Fig 01. Components of a microcontroller

Address bus carries address from CPU to select a particular location in memory

or I/O interface.

Data bus carries data read/written between CPU & memory or I/O interface.

Control buscarries timing signals such as READ & WRITE.


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Uses of microcontrollers

Electrical appliances

Automobile applications

Toys Calculators

Industrial process control


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PIC Microcontrollers

Peripheral Interface Controller (PIC) wasoriginally designed by General Instruments

In the late 1970s, GI introduced PIC 1650and 1655 RISC with 30 instructions.

PIC was sold to Microchip Incorporated

Features: low-cost, self-contained, 8-bit,

Harvard structure, pipelined, RISC, singleaccumulator, with fixed reset and interruptvectors.


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PIC Architecture

Fig 02 Havard architecture used

In PIC MCus

Address bus carries address from CPU to select a particular location in memory

or I/O interface.

Data bus carries data read/written between CPU & memory or I/O interface.

Control buscarries timing signals such as READ & WRITE.


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PIC Families

C implies CMOS technology; Complementary Metal Oxide Semiconductor

F insert indicates incorporation of Flash memory technology

Example: 16C84 was the first of its kind. It was later reissued as the 16F84,

incorporating Flash memory technology. It was then reissued as 16F84A.


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Programming a PIC

Components required

- PIC, 16F628A , or any PIC microcontroller

- MPLAB IDE (with C compiler

HTC)- Programmer ( ICD2, PicKit 2, etc)

Fig 6 Basic setup of programmer


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Programming languages

Machine code prone to error and time

consuming virtually non existent

Assembly small code size, efficient memory

use hence excellent good for time criticalroutines and applications

High Level languages fast product

development, easier to debug and maintain

C

Basic

Pascal


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Programming example 16F628A

35 instructions RISC

RAM 224 bytes

EEPROM

128 bytes Flash 2048 words ( 2 bytes per word)

Vcc +2.0V to +5V DC

Output - +5V, 25mA current Cost - less than ZAR40


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PIC 16F628A

Fig 4 Pin out of PIC 16F628A


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PIC 16F628A internal structure

Fig 03 Simplified block

diagram


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Fig 5 Program and data memory and peripherals of PIC 16F628A

PIC 16F628A features

35 instruction RISC controller

Cheap and low power requirements Flash based as opposed to CMOS parts

(reprogrammable multiple times)


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PIC 16F series assembly instruction set


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Basic Setup

Fig 6 ICD2 and Pickit 2


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Circuit diagram

Fig 7 PIC 16F887 blink LED example

circuit

Reset


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Sample program code

/* Blinks an LED connected toport B*/

BCF TRISB,0

BCF PORTB,0

LOOP:

pausems .1000

BSF PORTB, 0

pausems .1000

BSF PORTB, 0

GOTO LOOP

END ;control neverreaches here

void main(void)

{

TRISB0 = 0;//Make RB0 output

PORTB.RB0 = 0; // Make RB0 low

while(1) //loop forever

{

__delay_ms(500); // 1s delay

PORTB.RB0 = 1; // LED on

__delay_ms(500); // 1s delay

PORTB.RB0 = 0; // LED off

}

}

C programAssembly program


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Summary

Microcontrollers are essentially micro-computers,

with all the necessary components on one IC, (i.e.microprocessor core, memory and peripherals)

Microchip offers plethora of devices, with varyingcapabilities and cost

A lot of documentation and resources available

Easy to use, inexpensive and are easily re-

purposed.

Low power consumption and high reliability

Intoduction to Microcontrollers - PIC

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