INTERFACING

PIC MICROCONTROLLERS

 

Embedded Design

by Interactive Simulation

 

Martin Bates

 

Final Draft

March 2006

 

 

 

 

 

 

 


Contents

 

 

 

 

Part 1              Microcontroller

 

 

1       PIC HARDWARE

 

1.1              Processor System

1.2              PIC 16F877 Architecture

1.3              PIC Instruction Set

1.4              Special Function Registers

 

 

2       PIC SOFTWARE

 

2.1              Assembly Language

2.2              Software Design

2.3              ‘C’ Programming

 

 

3          CIRCUIT SIMULATION

 

3.1              Basic Circuit

3.2              Software Debugging

3.3              Hardware Testing

3.4              Hardware Implementation

 

 

 

 

Part 2              Interfacing

 

 

4          INPUT & OUTPUT

 

4.1              Switch Input

4.2              Switch Debouncing

4.3              Timer and Interrupts

4.4              Keypad Input

4.5              7-Segment LED Display

4.6              Liquid Crystal Display

 

 

5          DATA PROCESSING 

 

5.1              Number Systems

5.2              Conversion

5.3              Variable Types

5.4              Arithmetic

 

 

6          CALCULATE, COMPARE & CAPTURE

 

6.1              Calculator

6.2              Pulse Output

6.3              Period Measurement

 

 

7          ANALOGUE INTERFACING

 

7.1              8-bit Conversion

7.2              10-bit Conversion

7.3              Amplifier Interfaces

7.4              Transient & Frequency Response

7.5              Instrumentation Amplifier

7.7              Comparators

7.8              Op-amp Selection

7.9              Analogue Output

 

 

Part 3              Systems

 

 

8          POWER OUTPUTS

 

8.1              Current Drivers

8.2              Relays & Motors

8.3              Power Output Interfacing

8.4              Motor Interfacing

 

 

9          SERIAL COMMUNICATION

 

9.1              USART

9.2              SPI

9.3              I2C

 

 

10          SENSOR INTERFACING

 

10.1            Sensors

10.2            Sensor types

10.3            Amplifier Design

10.4            Weather Station

 

 

11          SYSTEM DESIGN

 

11.1            Base system

11.2            Memory System

11.3            Other PIC Chips

11.4            System Design

11.5            Other MCU families

 

 

 

 

 

 

 

Preface & Acknowledgements

 

I have my students to thank for this book – the good ones and the bad ones! The good ones have always helped, through our project work, to develop new ideas and solutions. Some have displayed outstanding engineering talent, and others have been so eager to learn as to make teaching a pleasure. But even those who struggle have had a positive impact because there is rarely enough time give individuals the help they need. So, one is forced to write it down, so that they would have no more excuses if they get it wrong!

 

Another spur to writing this book has been the development of the interactive design software which has made the job of learning and teaching electronics that much more enjoyable. The Proteus software used in this book has been developed by a talented team at Labcenter Electronics in the UK, led by John Jameson and Iain Cliffe. They have a world beating product, and I wanted to make a small contribution to encouraging students and engineers to use it. It allows us to bring electronic circuits to life on the computer screen instantly.

 

It has always been a problem in electronics that you cannot see a circuit working in the same way that a mechanical engineer can see a steam engine pumping up and down. Sure, we can see the screen flickering on a television, or an electric motor spinning, but you can’t see electrons or volts. As a result, it has always been that much more difficult to teach electronics. Proteus is a big step towards bringing electronics alive, as a such, helps us to participate more effectively in the communications and information revolution which continues to have a major impact on all our lives.

 

I would also like to thank the dedicated teachers of engineering that I have worked with, especially Melvyn Ball at Hastings College, and Chris Garrett at the University of Brighton, and, of course, Julia Bates.

 

Martin Bates

Hastings, UK

March 2006

 


 

 

 

 

 

Introduction

 

This book is a sequel to my first effort ‘PIC Microcontrollers, an Introduction to Microelectronics’. This attempted to provide a comprehensive introduction to the subject via single type of microcontroller, which is essentially a complete computer on a chip. The PIC was the first widely available device to use flash memory, which makes them ideal for experimental work. Flash memory allows the program to be replaced quickly and easily with a new version. It is now commonplace, not least in our USB memory sticks, but also in a wide range of electronic systems where user data needs to be retained during power down. Cheap flash memory microcontrollers have transformed the teaching of microelectronics – they are re-usable and the internal architecture is fixed, making them easier to explain. On the other hand, beginners can ignore the innards and treat them as a black box, and get on with the programming! The small instruction set of the PIC is also a major advantage – only 35 instructions to learn. Compare that with a complex processor such as the Pentium, which is quite terrifying compared with the PIC! The quality of the PIC technical documentation is also a major factor.

 

For these reasons, I set out to introduce the PIC into my teaching as widely as possible. At the same time, schools, universities and hobbyists were starting to using it , so continuity of learning was possible. Since there is never enough time to teach all the detail, I decided to set out a full description of the basic PIC device, the 16F84, and some representative applications. Although this particular chip is now redundant in terms of new products, the basic architecture is unchanged in current chips, so it is still a useful starting point.

 

My students and I soon graduated to the more powerful PIC 16F877. This is now used widely as a more advanced teaching device, because it has a full complement of interfaces: analogue input, serial ports, ICD, slave port and so on, plus a good range of hardware timers. A full description of this chip covers most of the features that higher level students need for project work with microcontrollers.

 

When interactive simulation of microcontrollers became available, a new dimension was added. We could now see them in action without having to spend a lot of time building and debugging hardware! These design tools allow even the inexperienced designer to create a working system relatively quickly. As a result, my next step was to the document the 16F877 and its applications, through the medium of interactive simulation.

 

Proteus© from Labcenter Electronics © consists of two main parts, ISIS and ARES. ARES is a layout package, which is used to create a PCB when the circuit has been designed. ISIS is the schematic capture and interactive simulation software used to create the circuit drawing and to test the circuit prior to building the real hardware. SPICE is a mathematical circuit modelling system which has been developed over many years – these models can now be used to bring the drawing to life. On screen buttons and virtual signal sources, for example, provide inputs to the circuit Output can be displayed on a voltage probe or on a virtual oscilloscope. Now that we have microcontroller simulation as well, we really are in business. The MCU can be dropped on the screen, a program attached and debugged instantly. Electronic design has never been so easy!

 

It is assumed that reader is familiar with the basics of microcontroller systems, as covered in the first book. This one follows on, and is divided into three main parts. In the first, the 16F877 hardware and programming, and the simulation system are introduced. In the second part, a range of interfacing techniques are covered; switches, keypads, displays, digital and analogue interfacing, data conversion and so on. In the third, power outputs, serial interfaces, sensors, and system design examples culminate in a design for a general purpose board which provides a platform for further developments.

 

Each topic is illustrated by designs based on the 16F877, so that the reader can concentrate on the interfacing, a not have to deal with different microcontrollers. All the circuits are available on the associated website (see links below). All schematics were produced using ISIS – and you can produce them to the same standard in your own reports. The designs can be downloaded and run along side the book. ISIS Lite, the introductory design package, can be downloaded free, with extra features available for a small registration fee. The 16F877 will simulate fully, and the software changed, but the hardware cannot be modified unless a licence is purchase for this device. The microcontroller models can be purchased for institution or professional use in packages – see the Labcenter website.

 

Get PICing!

 

 

 

 

 

 


LINKS, REFERENCES AND ACKNOWLEDGEMENTS

 

 

Labcenter Electronics

www.labcenter.co.uk

Manufacturer and supplier of Proteus VSM electronic design system

 

Microchip Technology Inc.

www.microchip.com

Manufacturer of the PIC microcontroller range and MPLAB IDE

 

Custom Computer Services Inc.

www.ccsinfo.com

Manufacturer and supplier of PIC CCS ‘C’ Compilers

 

 

Data references and trademark acknowledgements