The quintessential PIC microcontroller

Sid Katzen

The Quintessential PIC

Microcontroller

Sid Katzen, BSc, MSc, DPhil, MIEE, MIEEE, CEng

School ofElectrical and Mechanical Engineering, University ofUlster,

Newtownabbey, County Antrim BT37 OQB, UK

Series editor

Professor A.J. Sammes, BSc, MPhil, PhD, FBCS, CEng

CISM Group, Cranfield University, RMCS, Shrivenham, Swindon SN6 8LA, UK

In memory ofEva Jones

ISBN 1-85233-309-X Springer-Verlag London Berlin Heidelberg

British Library Cataloguing in Publication Data

Katzen,Sid

The qUintessential PIC microcontroner. - (Computer

communications and networks)

1.ProgJ~ablecontroners

I. Title

629.8'9

ISBN 185233309X

Library ofCongressCataloging-in-Publication Data

Katzen. Sid.

The quintessential PIC microcontroller. I Sid Katzen.

p. CDl. -- (Computer communications and networks)

Includes index.

ISBN 1-85233-309-X (alk. paper)

1. Programmable controllers. I. Title. II. Series.

TJ223.P76 K38 2001

629.8'9-dc21

00-066153

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as

permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced,

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sent to the publishers.

© Springer-Verlag London Limited 2001

Printed in Great Britain

2nd printing, with corrections 2003

3rd printing, 2004

The use ofregistered names, trademarks etc. in this publication does not imply, even in the absence ofa specific statement, that such names are exempt from the relevant laws and regulations and therefore

free for general use.

The publisher makes no representation, express or implied, with regard to the accuracy of the

information contained in this book and cannot accept any legal responsibility or liability for any errors

or omissionsthat may be made.

Typesetting: Camera-readyby author

Printed and bound at the Athenteum Press Ltd., Gateshead. Tyne and Wear

34/3830-5432 Printed on acid-free paper SPIN 10974791

Contents

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. VII

Part I The Fundamentals

1. Digital Representation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2. Logic Circuitry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 17

3. Stored Program Processing. 41

Part II The Software

4. The PIC16F84 Microcontroller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 77

5. The Instruction Set 105

6. Subroutines and Modules 135

7. Interrupt Handling 169

8. Assembly Language 195

9. High-Level Language 227

Part III The Outside World

10. The Real World 249

11. One Byte at a Time 267

12. One Bit at a Time 301

13. Time is of the Essence 357

VI Contents

14. Take the Rough with the Smooth 385

15. To Have and to Hold 425

16. A Case Study 449

Appendices

A. 14-bit Core Instruction Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469

B. Special Purpose Register Structure for the PIC16F874/7 471

C. C Instruction Set 473

D. Acronyms and Abbreviations 475

Index 479

Preface

Microprocessors and their microcontroller derivatives are a ubiquitous,

ifrather invisible, part of the infrastructure of our 21st century electronic

and communications society. In 1998 it was reckoned1 that hidden in ev￾ery home were about 100 microcontrollers and microprocessors; in the

singing birthday card, washing machine, microwave oven, television con￾troller, telephone, personal computer and so on. About 20 more lurked

in the average family car. For example monitoring in-tire radio pressure

sensors and displaying critical data through the car area network (CAN).

Around 4 billion such devices are sold each year to implement the

intelligence of these smart electronic devices, ranging from smart egg

timers through aircraft management systems. The evolution of the mi￾croprocessor from the first Intel device introduced 30 years ago in 1971

has revolutionised the structure of society, effectively creating the sec￾ond smart industrial revolution coming to fruition at the beginning of the

21st century. Although the microprocessor is better known in its guise

of powering the ubiquitous PC, in which raw computing power is the

goal, sales of such microprocessors as the Intel Pentium, represent only

around 2% of total volume. The vast majority of sales are of low-cost

microcontrollers embedded into a dedicated-function digital electronic

device, such as the smart card. Here the emphasis is the integration of

the core processor with memory and input/output resources in the one

chip. This integrated computing system is known as a microcontroller.

In seeking to write a book in this area the overall objective was to

get the reader up to speed in designing small embedded microcontroller￾based systems, rather than using microcontrollers as a vehicle to illus￾trate computer architecture in the traditional sense. This will hopefully

give the reader the confidence that even at such an introductory level,

he/she can design, construct and program a complete working embed￾ded system.

Given the practical mature of this material, real-world hardware and

software products are used throughout to illustrate the material. The mi￾crocontroller market is dominated by devices that operate on 8-bit data

(although 4- and 16-bit instances are available) like early microproces￾sors and unlike the 64-bit Intel Pentium and Motorola Power PC 'heavy

brigade'. In contrast the essence of the microcontroller lies in their high

INew Scientist, vol. 59, no. 2141, 4th July 1998, pp.139.

VIII The Quintessential PIC Microcontroller

system integration!low cost profile. Power can be increased by distribut￾ing processors throughout the system. Thus, for example, a robot arm

may have a microcontroller for each joint implementing simple local pro￾cesses and communicating with a more powerful processor making over￾all executive decisions.

In choosing a target architecture, both acceptance in the industrial

market, easy availability and low cost development software has made

the Microchip family one of the most popular choices as the pedagogic

vehicle in learning microprocessor/microcontroller technology at all lev￾els of electronic engineering from grade school to university. In particular

the reduced instruction set together with the relatively simple innovative

architecture reduces the learning curve. As well as its industrial and ed￾ucational roles, the PIC families are the mainstay of hobbyist projects; as

a leaf through any Electronic magazine will show.

Microchip inc. is a relatively recent entrant to the microcontroller mar￾ket with its family of Havard architecture PIC devices introduced in 1989.

By 1999, Microchip was the second largest producer of 8-bit units - be￾hind only Motorola.

The book is split into three parts. Part I covers sufficient digital, logic

and computer architecture to act as a foundation for the microcontroller

engineering topics presented in the rest of the text. Inclusion of this

material makes the text suitable for stand-alone usage, as it does not

require a prerequisite digital systems module.

Part II looks mainly at the software aspects of the mid-range PIC mi￾crocontroller family, its instruction set, how to program it at assembly

and high-level Ccoding levels, and how the microcontroller handles sub￾routines and interrupts. Although the 14-bit PIC family is the exemplar,

both architecture and software are comparable to both the 12- and 16-bit

ranges.

Part III moves on to the hardware aspects of interfacing and interrupt

handling, with the integration of the hardware and software being a con￾stant theme throughout. Parallel and serial input/output, timing, analog

and EEPROM data handling techniques are covered. A practical build and

program case study integrates the previous material into a working sys￾tem, as well as illustrating simple testing strategies.

With the exception of the first two and last chapter, all chapters have

both fully worked examples and self-assessment questions. As an exten￾sion to this, an associated Web site at

http://www.engj.ulst.ac.uk/sidk/quintessential

has the following facilities:

• Solutions to self-assessment questions.

• Further self-assessment questions.

• Additional material.

Preface IX

• Source code for all examples and questions in the text.

• Pointers to development software and data sheets for devices used in

the book.

• Errata.

The manuscript was typeset on a Siemens Scenic D Pentium 133 PC by

the author using a Y&Y implementation of It\TEX 2E and the Lucida Bright

font family. Camera-ready copy was produced in . pdf format and used

to directly generate plates at 1270dpi resolution. Line drawings were

created or modified with Autocad R13 and incorporated as encapsulated

PostScript files. Photographs were taken by the author using a Olympus

C-1400L 1.4 Mpixel digital camera - absolutely full of microcontrollers!

5.J. Katzen

University of Ulster at Jordanstown

December 2000

A reprint has given me the opportunity of revisiting some typesetting

issues; adding, updating and clarifying some material and upgrading a

few of the diagrams. In particular I would like to thank correspondents

from as far away as Hawaii, Canada and Switzerland who pointed out

errors (fortunately mainly minor) and other gremlins. These are listed

and acknowledged in the book's web site and have been corrected in this

reprint. Hopefully the majority of such gremlins have been exorcised,

but if you find any more or have any other suggestions, I will be happy to

take these on board and acknowledge such communications via the Web

site.

S.J. Katzen

University of Ulster at Jordanstown

October 2002

PART I

The Fundamentals

This book is about microcontrollers (MCUs). These are digital engines

modeled after the architecture of a stored-program computer and in￾tegrated on to a single very large-scale integrated circuit together with

support circuitry, memories and peripheral interface devices. Although

the MCU is often confused with its better-known cousin the micropro￾cessor in its role as the driving force of the ubiquitous personal com￾puter, the vast majority of both microprocessors and microcontrollers

are embedded into an assemblage of other digital components. The first

microprocessors in the early 1970s were marketed as an alternative way

of implementing digital circuitry. Here the task would be determined

by a series of instructions encoded as binary code groups in read-only

memory. This is more flexible than the alternative approach of wiring

hardware integrated circuits in the appropriate manner. The microcon￾troller is simply the embodiment of this original role of the integrated

computer.

We will look at embedded MCUs in a general digital processing context

in Parts II and III. Here our objective is to lay the foundation for this

material. We will be covering:

• Digital code patterns.

• Binary arithmetic.

• Digital circuitry.

• Computer architecture and programming.

This will by no means be a comprehensive review of the subject, but

there are many other excellent texts in this area2 which will launch you

into greater depths.

2Such as S.J. Cahill's Digital and Microprocessor Engineering, 2nd edn., Prentice Hall,

1993.

CHAPTER 1

Digital Representation

To a computer or microprocessor, the world is seen in terms of patterns

of digits. The decimal (or denary) system represents quantities in terms

ofthe ten digits 0...9. Together with the judicious use of the symbols +, -

and. any quantity in the range ± 00 can be depicted. Indeed non-numeric

concepts can be encoded using numeric digits. For example the American

Standard Code for Information Interchange (ASCII) defines the alphabetic

(alpha) characters A as 65, B = 66...Z = 90 and a = 97, b = 98... z = 122

etc. Thus the string "Microprocessor" could be encoded as "77, 105,99,

114,111,112,114,111,99,101,115,115,111,114". Provided you know

the context - that is, what is a pure quantity and what is text - then just

about any symbol can be coded as numeric digits.1

Electronic circuits are not very good at storing and processing a mul￾titude of different symbols. It is true that the first American digital

computer, the ENIAC (Electronic Numerical Integrator And Calculator)

in 1946 did its arithmetic in decimal2 but all computers since handle

data in binary (base 2) form. The decimal (base 10) system is really only

convenient for humans, in that we have ten fingers. 3 Thus in this chap￾ter we will look at the properties of binary digits, their groupings and

processing. After reading it you will:

• Understand why a binary data representation is the preferred base for

digital circuitry.

• Know how a quantity can be depicted in natural binary, hexadecimal

and binary coded decimal.

• Be able to apply the rules of addition and subtraction for natural binary

quantities.

• Know how to multiply by shifting left.

• Know how to divide by shifting right and propagating the sign bit.

• Understand the Boolean operations of NOT, AND, OR and XOR.

The information technology revolution is based on the manipulation,

computation and transmission of digitized information. This informa￾lOf course there are lots of encoding standards, for example the 6-dot Braille code for

the visually impaired.

2As did Babbage's mechanical computer of a century earlier.

3And ten toes, but base-20 systems are rare.

4 The Quintessential PIC Microcontroller

tion is virtually universally represented as aggregrates of binary digits

(bits).4 Most of this processing is effected using microprocessors, and

it is sobering to reflect that there is more computing power in a singing

birthday card than existed on the entire planet in 1950!

Binary is the universal choice for data representation, as an electronic

switch is just about the easiest device that can be implemented using a

transistor. Such 2-state switches are very small; they change state very

quickly and consume little power. Furthermore, as there are only two

states to distinguish between, a binary depiction is likely to be resistant to

the effects of noise. The upshot of this is that both the packing density on

a silicon chip and switching rate can be very high. Although a switch on

its own does not represent much computing power; five million switches

changing at 100 million times a second, manage to present at least a

fac;ade of intelligence!

The two states of a bit are conventionally designated logic 0 and

logic 1 or just 0 and 1. A bit may be represented by two states of any

number of physical quantities; for example electric current or voltage,

light, pneumatic pressure. Most microprocessors use OV (or ground) for

state 0 and 3 - 5V for state 1, but this is not universal. For instance, the

RS232 serial port on your computer uses nominally +12V for state 0 and

-12V for state 1.

A single bit on its own can only represent two states. By dealing with

groups of bits, rather more complex entities can be coded. For example,

the standard alphanumeric characters can be coded using 7-bit groups

of digits. Thus the ASCII code for "Microprocessor" becomes:

1001101 1101001 1100011 1110010 1101111 1110000 1110010

1101111 11 00011 11 00100 111 0011 111 0011 11 01111 111 0010

Unicode is an extension of ASCII and with its 16-bit code groups is able to

represent characters from many languages and mathematical symbols.

The ASCII code is unweighted, as the individual bits do not signify a

particular quantity; only the overall pattern has any significance. Other

examples are the die code on gaming dice and 7-segment code of Fig. 6.6

on page 146. Here we will deal with natural binary weighted codes,

where the position of a bit within the number field determines its value or

weight. In an integer binary number the rightmost digit is worth 2° = 1,

the next left column 21 = 2 and so on to the nth column which is worth

2n - 1• For example, the decimal number one thousand nine hundred and

ninety eight is represented as 1 x 103 +9 X 102 +9 X 101 +8 x 10° or 1998.

4The binary base is not a new fangled idea invented for digital computer; many cultures

have used base 2 numeration in the past. The Harappan civilization existed more than

4000 years ago in the Indus river basin. Found in the ruins of the Harappan city of

Mohenjo-Daro, in the beadmakers' quarter, was a set of stone pebble weights. These were

in ratios that doubled in the pattern, 1,1,2,4,8,16..., with the base weight of around 25g

(~ loz). Thus bead weights were expressed by digits which represented powers of 2; that

is, in binary.

1. Digital Representation 5

Table 1.1: 7-bit ASCII characters.

MS nybble - Oh lh 2h 3h 4h 5h 6h 7h

LS nybble OOOb 00lb 010b 011b 100b 101b 110b lllb

Oh OOOOb NUL DLE SP 0 @ P , P

1 h OOOlb SOH XON I 1 A Q a q

2h 0010b STX DC2 " 2 B R b r

3h 00llb ETX XOFF # 3 C S C 5

4h 0100b EOT DC4 $ 4 0 T d t

5h OIOlb ENQ NAK % 5 E U e u

6h 0110b ACK SYN & 6 F V f v

7h Ol11b BEL ETB , 7 G W 9 w

8h 1000b BS CAN ( 8 H X h x

9h 1001b HT EM ) 9 I Y i Y

Ah 1010b LF SUB * J z j z

Bh 1011b VT ESC + , K [ k {

Ch 1100b FF FS , < L \ I I

Dh 1101b CR GS - = M ] m }

Eh 1110b SO RS > N A n - Fh 1111b SI US / ? 0 - 0 DEL

In natural binary the same quantity is 1 X 210 + 1 X 29 + 1 X 28 + 1 X 27 +

1 X 26 +0 x 2S+0 X 24 + 1 X 23+ 1 X 22+0 X 21 + 1 x 20, or 11111 0011 01 b.

Fractional numbers may equally well be represented by columns to the

right of the binary point using negative powers of 2. Thus 1101 .11 b is

equivalent to 13.75. As can be seen from this example, binary numbers

are rather longer than their decimal equivalent; on average a little over

three times. Nevertheless, 2-way switches are considerably simpler than

10-way devices, so the binary representation is preferable.

An n-digit binary number can represent up to 2n patterns. Most com￾puters store and process groups of bits. For example, the first micro-

6 The Quintessential PIC Microcontroller

processor, the Intel 4004, handled its data four bits (a nybble) at a time.

Many current processors cope with blocks of 8 bits (a byte), 16 bits (a

word), or 32 bits (a long-word). 64-bit (a quad-word) devices are on the

horizon. These groupings are shown in Table 1.2. The names illustrated

are somewhat de-facto, and variations are sometimes encountered.

As in the decimal number system, large binary numbers are often

expressed using the prefixes k (kilo), M (mega) and G (giga). A binary kilo

is 210 = 1024; for example 64kbyte of memory. In an analogous way, a

binary mega is 220 = 1, 048, 576; thus a 1.44 Mbyte floppy disk. Similarly

a 2 Gbyte hard disk has a storage capacity of 2 x 230 = 2,147,483,648

bytes. The former representation is certainly preferable.

Table 1.2: Some common bit groupings.

Bit (1 bit) 0-1

(0 -1)

Nybble (4 bits) 0-15

(0000 - 1111)

Byte (8 bits) 0-255

(0000 0000 - 1111 1111)

Word (16 bits) 0-65,535

(0000 0000 0000 0000 - 1111 1111 1111 1111)

Long-word (32 bits) 0-4,294,967,295

(0000 0000 0000 0000 0000 0000 0000 0000 - 1111 1111 1111 1111 1111 1111 1111 1111

Long binary numbers are not very human friendly. In Table 1.2, bi￾nary numbers were zoned into fields offour digits to improve readability.

Thus the address of a data unit stored in memory might be 1000 1100

0001 0100 0000 101 Ob. If each group of four can be given its own

symbol, 0...9 and A...F, as shown in Table 1.3, then the address becomes

Be140Ah; a rather more manageable characterization. This code is called

hexadecimal, as there are 16 symbols. Hexadecimal (base-16) numbers

are a viable number base in their own right, rather than just being a con￾venient binary representation. Each column is worth 16°, 161 , 162 ••• 16n

in the normal way.s

Binary Coded Decimal is a hybrid binary/decimal code extensively

used at the input/output ports of a digital system (see Example 11.5 on

page 294). Here each decimal digit is individually replaced by its 4-bit

binary equivalent. Thus 1998 is coded as (0001 1001 1001 1000)Bcn.

This is very different from the equivalent natural binary code; even if it

is represented by Os and 1s. As might be expected, arithmetic in such

5Many scientific calculators, including that in the Accessories group under Windows 95,

can do hexadecimal arithmetic.