Interfacing PIC Microcontrollers 2 pptx

The small LCD screen is a good clue to the presence of an MCU Microcontroller Unit – it needs a programmed device to control it.. Although small, microcontrollers are complex, and we hav

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

Microchip Technology Inc., RS Components, Fairchild, Intel, Freescale (Motorola), National Semiconductor, Sensor Technics, Densitron, Honeywell, SGS Thomson, Maxim, ST Microelectronics, HBM, ARM, AVR Atmel, Texas, Vishay

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

Links, References and Acknowledgements

‘C’ Programming 47

Conversion 106

Arithmetic 112

Calculator 121

Current Loop 163 Comparators 165

SPI 205

Sensors 223

11 System Design 249

Contents

Part 1 Microcontroller

PIC Hardware

The microcontroller is simply a computer on a chip It is one of the most important developments in electronics since the invention of the microprocessor itself It is essential for the operation of devices such as mobile phones, DVD players, video cameras, and most self-contained electronic systems The small LCD screen is a good clue to the presence of an MCU (Microcontroller Unit) –

it needs a programmed device to control it Working sometimes with other chips, but often on its own, the MCU provides the key element in the vast range of small, programmed devices which are now commonplace

Although small, microcontrollers are complex, and we have to look carefully

at the way the hardware and software (control program) work together to understand the processes at work This book will show how to connect the pop-ular PIC range of microcontrollers to the outside world, and put them to work

To keep things simple, we will concentrate on just one device, the PIC 16F877, which has a good range of features and allows most of the essential techniques

to be explained It has a set of serial ports built in, which are used to transfer data

to and from other devices, as well as analogue inputs, which allow measurement

of inputs such as temperature All standard types of microcontrollers work in a similar way, so analysis of one will make it possible to understand all the others The PIC 16F877 is also a good choice for learning about micro-controllers, because the programming language is relatively simple, as compared with a microprocessor such as the Intel Pentium™, which is used in the PC This has

a powerful, but complex, instruction set to support advanced multimedia applications The supporting documentation for the PIC MCU is well designed,

and a development system, for writing and testing programs, can be down-loaded free from the Microchip website (www.microchip.com)

Processor System

The microcontroller contains the same main elements as any computer system:

• Processor

• Memory

• Input/Output

In a PC, these are provided as separate chips, linked together via bus connec-tions on a printed circuit board, but under the control of the microprocessor (CPU) A bus is a set of lines which carry data in parallel form which are shared by the peripheral devices The system can be designed to suit a partic-ular application, with the type of CPU, size of memory and selection of input/output (I/O) devices tailored to the system requirements

In the microcontroller, all these elements are on one chip This means that the MCU for a particular application must be chosen from the available range

to suit the requirements In any given circuit, the microcontroller also tends to have a single dedicated function (in contrast to the PC); this type of system is described as an embedded application (Figure 1.1)

Processor

In a microprocessor system or a microcontroller, a single processor block is in charge of all input, output, calculations and control This cannot operate without a program, which is a list of instructions that is held in memory The

Interfacing PIC Microcontrollers

CPU

Memory

Output Input

Figure 1.1 Block diagram of a basic microprocessor system

program consists of a sequence of binary codes that are fetched from memory

by the CPU in sequence, and executed (Figure 1.2)

The instructions are stored in numbered memory locations, and copied to

an instruction register in the CPU via the data bus Here, the instruction controls the selection of the required operation within the control unit of the processor The program codes are located in memory by outputting the address of the instruction on an address bus The address is generated in the program counter, a register that starts at zero and is incremented or modified during each instruction cycle The busses are parallel connections which transfer the address or data word in one operation A set of control lines from the CPU are also needed to assist with this process; these control lines are set up according to the requirements of the current in-struction

Decoding the instruction is a hardware process, using a block of logic gates

to set up the control lines of the processor unit, and fetching the instruction operands The operands are data to be operated on (or information about where

to find it) which follows most instructions Typically, a calculation or logical operation is carried out on the operands, and a result stored back in memory,

or an I/O action set up Each complete instruction may be 1, 2 or more bytes long, which includes the operation (instruction) code (op-code) itself and the operand/s (1 byte ⫽ 8 bits)

Address Instruction

0000 10010011

0001 01010001

0002 10000100

0003 00011001

0004 01011100

0005 xxxxxxxx

0006 xxxxxxxx etc etc

Instruction Register

Decoder Logic

Execution Logic

Control lines to system

Data bus Address bus ProgramCounter

Figure 1.2 Processor program execution