Easy PIC’n: A Beginner’s Guide to Using Pic16/17 Microcontrollers from Square 1

169 Pages·1996·16.01 MB·English

by  David Benson

,.....---------------------------.. ,
A BEGINNER'S GUIDE
TO USING PIC
MICROCONTROLLERS
FROM
VERSION 3.1
David Benson
Ple'n
A BEGINNER'S GUIDE TO USING
PIC MICROCONTROLLERS
FROM
DAVID BENSON
VERSION 3.1
NOTICE
The material presented in this book is for the education and
amusementofstudents, hobbyists, technicians and engineers.
Every effort has been made to assure the accuracy ofthis infor
mation and its suitability for this purpose. Square 1Electronics
and the author assume no responsibility for the suitability ofthis
information for any application nor do we assume any liability
resulting from use ofthis information. No patent liability is
assumed for use ofthe information contained herein.
All rights reserved. No part ofthis book shall bereproduced or
transmitted by any means (including photo copying) without
written permission from Square 1Electronics and the author.
Copyright © 1997 Revised April, 1999
TRADEMARKS
PIC is a registered trademark ofMicrochip Technology Inc. in
the U.S.A.
PICmicro is aregistered trademarkofMicrochip Technology, Inc.
PIC16j17 is aregistered trademark of Microchip Technology, Inc.
MPLAB is aregistered trademarkof Microchip Technology, Inc.
MPASM is aregistered trademark of Microchip Technology, Inc.
MPSIM is aregistered trademarkof Microchip Technology, Inc.
PICSTARTPlus is aregistered trademark ofMicrochip Technology, Inc.
MS-DOS is a registered trademark of Microsoft Corporation.
Windows is a registered trademark of Microsoft Corporation.
ISBN 0-9654162-0-8
PUBLISHER
Square 1 Electronics
P.O. Box 501
Kelseyville,CA 95451 U.S.A.
voice [phone]
FAX [phone]
EMAIL [email protected]
http://www.sq-1.com
A BEGINNER'S GUIDE TO USING
PIC MICROCONTROLLERS
FROM
INTRODUCTION 1
PIC PRODUCT OVERVIEW 3
PIC16F84 5
Pins and Functions 5
Package 5
Clock Oscillator 6
Configuration bits 7
Reset 7
Ports 8
Special Features 8
Watchdog Timer 8
Power-up Timer 8
Sleep Mode 8
PIC16 Architecture 9
Program Memory 9
Weird Hex Notation 9
File Registers 10
Working Register (W) 11
Option Register 11
Stack 11
Reset Vector 11
Interrupt Vector 11
Option Register 12
Program Counter 13
Status Register 15
CIRCUIT FOR EXPERIMENTS 16
'84 On A Board 17
CHOOSING DEVELOPMENT TOOLS 20
MPLAB/Windows vs. MPASM/MS-DOS 20
Choosing A Device Programmer 20
USING AN ASSEMBLER 22
Source Code For The Assembler 22
Semicolon (;) 23
Tabs 24
Style 25
Headers 26
Labels 26
Equates 27
Literals 28
Origin 29
End 30
Program Format 30
Files Used By Assembler 31
Files Created By Assembler 31
Preventing Some Gotchas 33
USING THE MS-DOS BASED MPASM ASSEMBLER 34
How To Assemble A Program 34
MPLAB OVERVIEW - GETTING STARTED 37
Using MPLAB - Getting Started 37
Toolbars 37
Select Development Mode And Device Type 38
Project 38
Text Editor 39
Edit Project 39
Assembler 40
More MPLAB Operations 40
PROGRAMMING A DEVICE 41
WRITING PROGRAMS 43
Programming Concepts 43
Instruction Set 46
Weird Move Instruction 48
Instruction Format For The Assembl~r 49
Byte-Oriented Instructions 49
Bit-Oriented Instructions 50
Literal Instructions 50
Control Instructions (CALL and GOTO) 50
Destination Designator (d) 51
Hexadecimal Numbers vs . MPASM Assembler 52
Binary And Decimal Numbers vs. MPASM Assembler 53
ASCII Characters vs . MPASM Assembl er 53
Addressing Modes 54
Immediate addressing 54
Direct Addressing 54
Indirect Addressi ng 54
Rel at ive Addressing 55
Use Of The RETLW Instruction For Accessing 56
Tables of Data Via Rel at i ve Addressing
using The Ports 58
Data Direction 58
Port Read/Write 58
Flags 59
Simple Data Transfers 59
Loop - Endless 61
Loop With a Counter 62
Loop Until 65
Comparisons 66
Bit Manipulation Using Bit Manipulation 69
Instructions
Bit Manipulation Using Logic Instructions 71
Using Bit Manipulation 73
Sequencing 77
Subroutines 80
Time Delay Loop 82
Lookup Tables 91
INTERRUPTS 94
Interrupt Control Register 95
Interrupt Sources 96
External 96
Timer/Counter 96
Port B Interrupt On Change - Bits 7,6,5,4 97
Global Interrupt Enable Flag 97
Saving Status During An Interrupt (Context Saving) 97
Where To Put The Interrupt Service Routine 98
Interrupt Latency 99
Multiple Interrupt Sources 100
Example - External Interrupt 101
TIMINGANDCOUNTING 107
Digital Output Waveforms 107
Timing And Counting Using The PIC16F84's TMRO 108
On-Board Timer/Counter
Prescaler 110
Changing Prescaler Assignment 111
Using The Timer/Counter 112
Timer/Counter Experiments 113
Digital Output Using TMRO - Internal Clock 113
Single Time Interval - Internal Clock 115
Single Time Interval - External Clock 118
Free Running Mode - Internal Clock 121
Free Running Mode - External Clock 125
Counting Events (Pulses) 126
PIC16C54 131
Pins And Functions 132
Packages 132
Clock Oscillator 133
Configuration bits 133
Ports 133
Architecture 134
Program Memory 134
File Registers 134
Stack 135
Reset Vector 135
Program Counter 136
Option Register 136
Status Register 137
No Timer/Counter Overflow Interrupt/Flag Out put 137
Fewer Instructions 137
PIC16C54 Programming Example 138
Timing And Counting 139
Timer/Counter Description 141
Using The Timer/Counter 142
Timer/Counter Experiment 142
MENDING OUR WAYS 143
Sink vs. Source 143
File Register Bank Switching 144
Bank Switching Demo 145
Interrupts And Bank Switching 148
Program Memory Paging 148
Include Files 148
I/O CONVERSION 151
Input Conversion 151
Output Conversion 154
MORE PIC'n BOOKS 157
APPENDICES
Appendix A - Sources 159
Appendix B - Hexadecimal Numbers 161
Appendix C - Program Listings vs. Page Number 162
INTRODUCTION
The PIC was originally designed as a Peripheral Interface Controller (PIC) for a lri-bit micro
processor. It was essentially an I/O controllerand was designed to be very fast. It had a small
microcoded instruction set. This design became the basis for Microchip Technology's
PICI6C5X family ofmicrocontrollers.
The PICI6F84 (or PICI6F84A) microcontrolleris unique because its programmemory is made
usingFlash technology. It can be programmed, tested in-circuit and reprogrammed ifnecessary
in amatterofafew minutes and without the need for aUV EPROM eraser. It is asmall device
(18-pin), readily available to all including hobbyists and students at a cost of $6.00 (at this writ
ing) in single quantity.
The PICI6F84replaces the PICI6C84 which will soon be obsolete.
Think ofthe PICI6F84 as a custom I/O handler. It looks at its inputs and, based onwhat it sees,
it sends signals out its outputs. Youcan customize it to do what you wantviaprogramming. It
is not a heavy duty numbercruncheror data manipulator.
The MPASM (tm) assemblerfrom Microchip Technology (manufacturer ofPIC family) is the
PIC assemblerofchoice for use in this book because:
• It is free from Microchip.
• Most people who are into PICs speak "MPASM".
• Most examples in magazines and on the Internet are written
in the MPASM dialect.
• It is included in MPLAB (tm), a populardevelopment software package (available
free from Microchip).
A variety ofprogrammers are available for the PICI6F84 from independent programmermanu
facturers (see sources in Appendix A). Some range incost from $40 to $80. Some come with
their own assemblers but will accept hex files created by MPASM (detailslater).
Microchip makes the PICSTART Plus (tm) programmer which will program all PIC microcon
trollers. The cost is currently about $200.
The PICI6F84, MPASM assembler (either stand alone or aspart ofMPLAB) and a low cost
PICI6F84 programmermake avery inexpensive development system and a great way to get
started creating microcontroller based projects.
What you learn using the PICI6F84 is directly applicable to the whole line of PIC microcon
trollers. The approach taken with the PICI6F84 in the first part ofbook is backwards compati
ble with the PICI6C54 (explained toward the end of the book). The hasslesof file register bank
switching and program memory paging are avoided as theyare confusing to a beginner but man
ageable after some experience is gained.
1
Learning how PICs work and how to apply them involves study in three areas:
• IBM compatiblecomputer use (as needed).
• Assembler.
• PIC itself.
PICs are not easy to write code for by hand because they are not intuitive. Many instructions
require settingor clearing a bit to specify the destination for the result ofexecuting the instruc
tion. This is OK as an initial learning experience, but would become tedious very soon. So use
of "power tools" is essential. This means learning to use an IBM compatiblecomputerifyou
haven'talreadydone so. It also means learning to use an assemblerwhich converts English-like
readable instructions into machine language understood by the PIC itself.
Finally,learning about the PIC's inner workings ispossible once use ofthe power tools is under
stood.
The objectis to make this process as easy and enjoyable as possible. Once you get through this
and you have programmed a PIC16F84 for the first time, a whole new world awaits. You will be
able to create more interesting projects and have more fun!
The usual approach to teaching the use of the PIC has been to get into all ofthe assemblercom
mands and then show advanced examples. There has been no simple example showing how to
get started. As usual,only 5 percent of this information is needed to get started, but which 5 per
cent. The approach taken here will be to give you the 5 percentyou need to get going.
The assumptionis made that you know how to do the following on an IBM compatible comput
er:
• Create a new directory called \PIC.
• Copy the contents of a floppy disk to the directory\PIC.
• Use a simple text editor to create a text file, save it,make a copy ofit, printit, and
copy it to the directory\PIC.
2
PIC16/17 PRODUCT OVERVIEW
This book uses the PIC16F84 and later the PIC16C54 as examples to get you started. The
emphasis is on the base-line (12-bit core) and mid-range (14-bit core) products. The 12-bitcore
designates the instruction word length. Youreally won'tcare how many bits there are in an
instruction word, but it is the basis on which Microchip divides up their product line. Thefol
lowing brieftables are for reference:
Base-Line Mid-Range
12-bit Core 14-bit Core
Stack Levels 2 8
Interrupts No Yes
Instructions 33 35*
Serial Programming No Yes
File Registers 128 max ** 256 max **
Example PIC16C54 PIC16F84
* We will use 37 - details later
** Varies with part number
PARTS IS PARTS
As the Microchip rnicrocontrollerproduct line grows,and I am glad thatit is,the part numbering
convention/system seems to be getting a bit involved. Also, the microcontroller product line
designation has been changedfrom PIC16/17 (tm) toPICmicro (tm), Microchip is going to do
what itwill. Youand I, however, need a way tokeep things straight between us. The real key to
sanity here is to recognize that there are three fundamental product groups in terms ofhow they
function and, to some extent, how program code must be writtenfor them. The three product
groups have 12-bit, 14-bit and 16-bitcores. Wedon't reallycare how many bits arein an
instruction word. Wejust need to know which set of rulesand features apply when writingcode
for a selected chip. Here are some popularexamples:
Device Core Size Pins
PIC12C508 12 8
12C671 14 8
16C54 12 18
16C554 14 18
16C63 14 28
16C71 14 18
16C74 14 40
16F84 14 18
3