Table Of ContentInterfacing PIC Microcontrollers
Interfacing PIC Microcontrollers
Embedded Design by Interactive Simulation
Martin Bates
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Preface
The PIC is one of the biggest selling small microcontrollers. When it first became
available, it was not only technically innovative, but helped to make the teaching of
microelectronics much more interesting. A small controller with flash memory meant that a
great variety of student projects could be realised quickly and easily. It helped that the
development toolkit was free as well.
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 cannot see electrons or volts directly. As a result, it has always been that bit more
difficult to learn electronics.
Interactive electronic design software is the answer. The Proteus VSM (Virtual System
Modelling) software used in this book has been developed by Labcenter Electronics in the
UK. It brings circuits to life on the computer screen and makes learning electronics more
effective and more fun. It is also a full-scale professional product, and will take the student
electronic engineer seamlessly into commercial design work.
This book is intended to support electronic learning wherever it takes place, at college,
at work or in the home. Please enjoy!
Martin Bates
March 2013
xiii
Introduction
This book is the second edition of the sequel to ‘PIC Microcontrollers, an Introduction
to Microelectronics’, which attempted to provide introduction to the subject via a single
type of microcontroller. It explores the basic techniques for connecting the PIC to
peripheral devices and the outside world. It shows how to connect simple input and output
devices, such as switches, sensors, displays and motors, as well as demonstrating
communication methods that allow the PIC to communicate data with other devices,
including intelligent sensors. The second edition has been extensively revised, updated
and expanded.
A domestic inkjet printer is an example of a product that contains a range of sensors,
drives and displays. It typically has a wireless data link to receive the page data, at least
two motors to feed the paper and position the print head, and a microcontroller to output
the signals to the print cartridge inkjets and generally coordinate the action. Take an old
one apart and have a look! Another good example is the digital camera. In fact, most small
electronic products contain a microcontroller that provides its core functions. A smoke
detector with a PIC microcontroller is shown in Figure I.1.
r
The PIC microcontroller was the first widely available device to use flash memory,
which made it ideal for prototyping and experimental work. Flash memory, as used in
memory cards and sticks, allows the application program to be replaced quickly and easily
with a new version. Cheap flash memory microcontrollers have also transformed the
teaching of microelectronics (cid:1) they are re-usable and the internal architecture is fixed,
making them easier to understand. The small instruction set of the PIC is also a major
advantage (cid:1) there are only 35 instructions to learn in the main microcontroller unit (MCU)
used in this book.
r r
The free development system MPLAB provided by Microchip Inc. is another reason
for using the PIC range. In addition to the program editor and project management features,
it includes a text-based simulator which allows the program to be tested prior to
downloading, potentially saving a lot of time debugging in hardware. However, this only
tests the program itself, not the circuit in which it is connected.
xv
xvi Introduction
Figure I.1
Smoke detector withPIC controller.
r r
Proteus from Labcenter Electronics allows a PIC to be simulated in circuit. It consists
of two main parts, ISIS and ARES. ISIS is the schematic capture and interactive simulation
package used to create the circuit schematic and to test the circuit prior to building
the real hardware. On-screen buttons and virtual signal sources provide inputs to the circuit.
Output (analogue or digital) can be displayed on a signal probe, a virtual instrument
or graph. An MCU can be dropped on the screen, the circuit drawn, a program attached
and tested immediately on screen.
When the application is working correctly in simulation mode, a PCB can be designed
by exporting a netlist (list of components and connections) from ISIS into the ARES layout
package. The resulting PCB files can be output to a production system or sent to a
specialist manufacturer. The final stage is then to assemble the board and test the hardware.
After using Proteus VSM, it should work first time!
This book is built around particular devices and tools, because it allows specific examples
to be used. It is assumed that at a later stage, with more experience, the reader will be
able to evaluate these against competing products and choose the most appropriate for any
given design task. Each topic is illustrated by designs based on the well-established PIC
16F877A, but it will be replaced in the readers’ own designs with a more recent device
such as the 16F887 chip.
All the circuits are available on the support website www.picmicros.org.uk. All schematics
were produced using ISIS (cid:1) and you can produce them to the same standard in your
Introduction xvii
Host
development
software
Programmer
connector
Prototyping
target board
Prototype
Programmer
circuit
module
components
Figure I.2
PICDEMdevelopmentkit. Courtesy of Microchip Inc.
own reports. The microcontroller models can be purchased in packages for institutional or
professional use from www.labcenter.com. Currently, a Proteus starter kit including models
for the PIC 16F84A, 16F877A and 18F452 can be purchased for only d150.
Microchip provides an extensive range of demonstration and development kits to support
their microcontroller product range (cid:1) see www.microchip.com for all product details.
A basic development kit is illustrated in Figure I.2, which consists of a prototyping target
board, a selection of hardware components including some small PIC chips, programmer
module and development system software that is loaded onto a host PC. A circuit is
built on the prototyping area, for example a motor interface, and a suitable PIC chip fitted
into one of the sockets on the board. The motor control program can be written in MPLAB
on the host computer, debugged in MPSIM, the Microchip simulator, downloaded to the
target board and the hardware tested.
However, it is preferable to test the application before constructing the hardware, in case
changes are needed. It is much quicker and easier to change the circuit, or the program,
on screen, rather than in hardware. ISIS allows the program to be entered, assembled and
attached to the on-screen chip for interactive testing within the virtual circuit. A typical
simulation screen is shown in Figure I.3.
The book is structured in three parts. Part 1 reviews PIC microcontroller architecture and
programming, Part 2 introduces PIC interfacing techniques and Part 3 covers PIC system
design and implementation.
xviii Introduction
FigureI.3
Base board simulation screenshot.
In Chapter 1, a standard PIC microcontroller, the 16F877A, is described in detail, based
mainly on its data sheet. Chapter 2 outlines the programming process, using only MPLAB
tools, and Chapter 3 describes the application development process using Proteus VSM.
In Chapter 4, basic input and output devices are introduced, while Chapter 5 describes
the techniques for data representation and conversion, Chapter 6 covers all aspects
of analogue signal conditioning and, in Chapter 7, power output interfacing is introduced,
concentrating on motor drives.
Chapter 8 outlines the operation of the main PIC serial communication ports, and Chapter 9
describes a wide range of sensors for monitoring and measurement applications. Chapter 10
concludes with a consideration of MCU selection and the principles and practice of system
design.
The book was originally designed to support project development by students at all levels.
It may therefore sometimes state what is obvious to more experienced engineers; hopefully
this is not too irritating, and they too will find something of interest within!
Links and Acknowledgements
Support Website
www.picmicros.org.uk
Author’s website with related PIC books and application file downloads
Follow the link to demo applications in INTAPPS2.ZIP containing:
(cid:129) VSM project file app2.pdsprl
(cid:129) PIC source code app2.asm (in MCU folder)
(cid:129) PIC debug file debug.cof (in MCU folder)
Labcenter Electronics
www.labcenter.com
Manufacturer and supplier of Proteus VSM electronic design system
(cid:129) Download demo version of VSM
(cid:129) Purchase MCU package licence
(cid:129) Tutorials and product information
Microchip Technology Inc.
www.microchip.com
Manufacturer of the PIC microcontroller range and MPLAB IDE
(cid:129) Download data sheets
(cid:129) Information on development tools
(cid:129) Download MPLAB development system
Custom Computer Services Inc.
www.ccsinfo.com
Manufacturer and supplier of PIC CCS ‘C’ Compilers
Please search online by name for product datasheets other than Microchip.
Use of all manufacturers’ trademarks and data is gratefully acknowledged.
Thanks in particular to Iain Cliffe at Labcenter Electronics.
xix
CHAPTER 1
PIC Hardware
Summary
(cid:129) The microcontrollercontains aprocessor, memoryand input/output devices
(cid:129) The program is stored in flash ROM memoryin numbered locations
(cid:129) The P16F877A family uses only 35instructions
(cid:129) The P16F877A stores a maximum8k 3 14 instructions inflash ROM
(cid:129) The P16F877A has 368 bytesof RAM and 5 ports(33 I/O pins)
(cid:129) The program is executed insequence, unless there is ajump instruction
(cid:129) The program counter tracks the current instruction address
(cid:129) Aconfiguration word is need toselect the clocktype andotherchip options
(cid:129) The program source code (.ASM) is assembled into machine code (.HEX)
(cid:129) Machine code is downloadedto the chip and the application hardware tested
The microcontroller is a complete computer on a chip. When introduced, it was one of
the most significant developments in electronics since the invention of the microprocessor
itself and is essential in the operation of such devices as mobile phones, DVD players,
video cameras, and most self-contained electronic systems. Working sometimes with other
chips, but often on its own, the microcontroller unit (MCU) provides the key element in
the vast range of small, programmed devices that are now commonplace.
Although small, microcontrollers are complex, and we have to look carefully at the
way the hardware and firmware (control program) work together to understand the
processes at work. This book will then show how to connect the popular PIC range of
microcontrollers to the outside world and put them to work. To keep things simple,
we will concentrate on one device, the PIC 16F877A, which has a good range of features
that allows most of the essential techniques to be explained. It has a set of serial ports
built in that are used to transfer data to and from other devices, as well as analogue
inputs, which allow measurement of inputs such as temperature. All microcontrollers
work in a similar way, so analysis of the PIC MCU will go a long way to understanding
all such devices.
This chip has been around some time and is no longer the best choice for new designs.
The 16F887 is a more recent equivalent and should be used as a pin compatible
InterfacingPICMicrocontrollers.
DOI:http://dx.doi.org/10.1016/B978-0-08-099363-8.00001-7 3
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