PIC Microcontroller Introduction

8/10/2019 PIC Microcontroller Introduction

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Bi ging Kthut Vi x l

Microcontroller Architecture

PIC16F Family

i hc Nng

Trngi hc Bch Khoa

Khoain t Vin ThngB mn K thut My tnh

Instructor: Phm Xun Trung


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Reference Material

PIC 16F87X data sheet PICMicro Mid-Range MCU Family Reference

Manual Available on course web page


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The Microchip PIC ucontrollers

http://www.microchip.com Characteristics

types; speeds; I/O pins; Analog to Digital

Converters; Capture/Compare modules

Programming (MPLab)

Instruction set

Implementations and Examples


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MICROCONTROLLER

Programmable Chip Same idea as PC, but

on much smaller

scale


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Why a microcontroller isneeded?

Sensors Microcontrollers Actuators


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Variety of microcontrollers

Atmel AT90S8535Motorola 68HC11

Intel - 8051

Texas Instruments -Microchip PIC16F84, PIC16F877


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Why PIC microcontrollers?

Easy to programBetter online documantation


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Introduction

What is PIC?

- A family of Harvard architecture microcontrollers madeby Microchip Technology

- Derived from the PIC1650 originally developed byGeneral Instrument Microelectronics Division.

- The name PIC was originally an acronym for

"Programmable Intelligent Computer(?)Peripheral Interface Controller (?)


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Introduction

Why PIC is popular? low cost ,wide availability with high clock speed

availability of low cost or free development tools

Only 37 instructions to remember

serial programming and re-programming with flashmemory capability

Its code is extremely efficient, allowing the PIC to runwith typically less program memory than its largercompetitors

PIC is very small and easy to implement for non-

complex problems and usually accompanies to themicroprocessors as an interface


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Introduction


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REVIEW

MCU Architectures

Hardvard vs Von Neumann

RISC vs CISC Pipelining


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Two Different Architectures

Harvard Architectures

Used mostly in RISC CPUs

Separate program bus and databus: can be of different widths

For example, PICs use: Data memory (RAM): a small

number of 8bit registers

Program memory (ROM): 12bit,14bit or 16bit wide (in EPROM,FLASH, or ROM)

Von-Neumann Architecture

Used in: 80X86 (CISC PCs)

Only one bus between CPU andmemory

RAM and program memory sharethe same bus and the samememory, and so must have the

same bit width Bottleneck: Getting instructions

interferes with accessing RAM


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RISC vs. CISC

Reduced Instruction Set

Computer (RISC)

Used in: SPARC, ALPHA,

Atmel AVR, etc.

Few instructions

(usually < 50) Only a few addressing

modes

Executes 1 instruction in 1

internal clock cycle (Tcyc)

Complex Instruction Set

Computer (CISC)

Used in: 80X86, 8051,

68HC11, etc.

Many instructions

(usually > 100) Several addressing modes

Usually takes more than 1

internal clock cycle (Tcyc)

to execute


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Pipelining in PIC

Instruction Pipeline FlowInstruction Pipeline Flow


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V d:

Pipelining for Instruction Execution


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The Microchip PIC family


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Baseline Architecture


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PICMicrocontroller Families

PIC microcontrollers are designed using theHarvard Architecture which includes:

Microprocessor unit (MPU)

Program memory for instructions

Data memory for data

I/O ports

Support devices such as timers


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Microcontroller withthe Harvard Architecture


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Characteristics

RISC CPUs 8-bit

16-bit

Number of I/O pins: 4-70

Memory types and sizes:

Flash; OTP; ROM

0.5k 256k


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Speeds

All PICs require oscillators to executeinstructions:

Internal* (low speeds, up to 8 MHz)

External (high speeds, up to 40 MHz)

Instructions are executed at least at

oscillator speed (4 clocks/instruction)

(*Note: not all PICs have internal oscillators)


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A/D converters and C/C modules

All PICs have between 0 and 16 A/Dconverters with 8/10-bit resolution

8-16 bit Timers/Counters

Comparator Modules (0-2)


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The PIC Family: Speed

Can use crystals, clock oscillators, or even an RC circuit.Can use crystals, clock oscillators, or even an RC circuit. Some PICs have a built in 4MHz RC clock, Not very accurate,Some PICs have a built in 4MHz RC clock, Not very accurate,

but requires no external components!but requires no external components!

Instruction speed = 1/4 clock speed (Instruction speed = 1/4 clock speed (TcycTcyc = 4 *= 4 * TclkTclk))

All PICs can be run from DC to their maximum specified speed:All PICs can be run from DC to their maximum specified speed:

40MHz18Cxxx

33MHz17C4x / 17C7xxx

20MHz16Cxxx

10MHz12C67x

4MHz12C50x


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Clock and Instruction Cycles

Instruction ClockInstruction Clock Clock from the oscillator enters a microcontroller via OSC1 pin where internal circuit of a

microcontroller divides the clock into four even clocks Q1, Q2, Q3, and Q4 which do not overlap. These four clocks make up one instruction cycle (also called machine cycle) during which one

instruction is executed.

Execution of instruction starts by calling an instruction that is next in string.

Instruction is called from program memory on every Q1 and is written in instruction register on Q4.

Decoding and execution of instruction are done between the next Q1 and Q4 cycles. On the

following diagram we can see the relationship between instruction cycle and clock of the oscillator

(OSC1) as well as that of internal clocks Q1-Q4. Program counter (PC) holds information about the address of the next instruction.


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The PIC Family: ProgramMemory

Technology: EPROM, FLASH, or ROM

It varies in size from one chip to another.

-- examples:examples:

16bit

instructions

16384 (16k)17C766

14bitinstructions8192 (8k)16F877

14bit

instructions

1024 (1k)16C711

12bitinstructions

51212C508


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Family Core Architecture Differences

The PIC Family: Cores 12bit cores with 33 instructions: 12C50x, 16C5x

14bit cores with 35 instructions: 12C67x,16Cxxx

16bit cores with 58 instructions: 17C4x,17C7xx

Enhanced 16bit cores with 77 instructions: 18Cxxx


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The PIC Family: Data Memory

PICs use general purposePICs use general purpose File registersFile registers for RAM (eachfor RAM (each

register is 8bits for all PICs)register is 8bits for all PICs)

-- examples:examples:

902B RAM17C766

368B RAM + 256B of

nonvolatile EEPROM

16F877

36B RAM16C71C

25B RAM12C508


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PIC Programming Procedure

For example: in programming an embedded PIC featuring electronicallyerasable programmable read-only memory (EEPROM). The essential

steps are:

Step 1: On a PC, type the program, successfully compile it and then

generate the HEX file.

Step 2: Using a PIC device programmer, upload the HEX file into the PIC.

This step is often called "burning".

Step 3: Insert your PIC into your circuit, power up and verify the program

works as expected. This step is often called "dropping" the chip. If it isn't,you must go to Step 1 and debug your program and repeat burning and

dropping.


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PIC Programming Procedure


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Memory Unit


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Memory Unit

Memory:

Registers:

Address:


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CPU


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CPU


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Input-output unit

Those locations we've just added are called"ports".

There are several types of ports : input, output or

bidiectional ports. When working with ports, first of all it is necessary

to choose which port we need to work with, and

then to send data to, or take it from the port.


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Input-output unit


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Input-output unit

Input register:

Output register:

Connecting with other unit:


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Time unit


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Time unit

Counter:

Excute:


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Watchdog

Trong trng hp chng trnh b kt, b m sreset li vi x l khi trn.


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Watchdog

Why a Watchdog timer is needed?

Excute:


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Analog to Digital Converter


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Analog to Digital Converter

a Analog to Digital Converter why is needed?

Excute:


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PIC16F Microcontroller

Families


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Architecture of the PIC16F

Buses: Communication lines for transferring data within the processor.

Oscillator: Used to drive the microprocessor, clocking data andinstructions in the processor.

Timing: The PIC has an internal divide by 4 whereby 4 oscillator pulses

form one clock pulse. This makes instruction times easy to calculate.

Most instructions (except calls and returns and otherinstructions involving jumps and branches) take one clock

cycle, so with a 4MHz oscillator (divided by 4), instructions

take 1s.

The calculation of execution times is important. We will use

timed delay subroutines in the laboratory to slow down traffic lightLED sequences (otherwise pedestrians will have 1s to cross the

road!) The PIC16F also has a hardware timer, TMR0, which we

shall consider later.


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Architecture - continuedProgram counter: The program counter stores the current programposition. After each instruction the program counter is incrementedautomatically so that it points to the location of the next instruction ordata in memory.

Stack: The stack is used to save program counter contents whensubroutines are called. The PIC16F has an 8-level stack.

Reset vector: On power-up or reset, the PIC16F will go to program

memory and begin executing instructions sequentially.Interrupt vector: In the PIC16F, this points to 0x04, so that if aninterrupt occurs, the first instruction to be executed will be at thislocation. Interrupts are configured in the interrupt control register.

Status register: The status register is a very important registerwhich

contains all the arithmetic status of the ALU and Reset status. Thecontents of the status register are updated after certain instructions

which modify the W (working) register.


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Microcontroller FeaturesMicrocontrollers now come with a wide range of features, forexample, watchdog timers, sleep/wakeup modes, powermanagement, powerful I/O channels, and so on.

Watchdog timer

A watchdog timer provides a means of graceful recovery from asystem problem. This could be a program that goes into an

endless loop, or a hardware problem that prevents the programfrom operating correctly.

If the program fails to reset the watchdog at some predeterminedinterval, a hardware reset will be initiated. The bug may still

exist, but at least the system has a way to recover. This isparticularly useful for unattended systems.

See the CLRWDT instruction.


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The PIC 16F87x SeriesMicrocontrollerSome of the characteristics of the PIC 16F87x series

High performance, low cost, for embedded applications Only 35 instructions

Each instruction is exactly one word long and is

executed in 1 cycle (except branches which take two

cycles )

4K words (14bit) flash program memory

192 bytes data memory (RAM) + 128 bytes EEPROM

data memory

Eight level deep hardware stack

Internal A/D converter, serial port, digital I/O ports,

timers, and more!


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Example: PIC 16F877A

8 kbytes of FLASH Program Memory

368 bytes of Data Memory (RAM)

256 bytes of EEPROM Data Memory

33 input or output pins

20 MHz operating speed(200 ns instruction

cycle)

Max. 25 mA current from an output pin


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Example: PIC16F877A

5/6 Programming pins

8 A/D channels

2 Oscillator Inputs

2 RS-232 inputs

33 I/O ports


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PIC16F877A


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Microprocessor Unit Registers

Program Counter (PC)

Bank Select Register (BSR)

File Select Registers (FSRs)

Control unit


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PIC16F - Address Buses

Address bus

Address bus for program memory addressing

capacity:

Address bus for data memory addressing

capacity:

330_02 58


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Data Bus and Control Signals

Data bus

Control signals


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PIC16F877A Pin Layout

PORTA PORTB

PORTE

PORTC PORTC

PORTD

PORTD

ADCinputs

Counter

0

external

input


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PIC 16F877A pin out


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PIC Program Memory The PIC16F877 8192 (8k) 14bit instructions

If interrupted, programexecution continues from

here

When thecontroller is reset,

program execution

starts from here

Takes a max of 8 addresses, the

ninth address will write over the first.


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PIC Memory

program memory:

Data Memory :


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PIC Data Memory

The data memory is devided into 4 memory banks

The most

important

registershave

addresses

in all the

four

banks


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Special Function RegisterSTATUS Register


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PIC Peripherals

Each peripheral has a set of SFRs to control its operation.

Different PICs have different on-board peripherals


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PIC Peripherals: Ports (Digital I/O)

Ports are basically digital I/O pins which exist in all PICs

The PIC16F877A have the following ports:

PORT A has 6 bit wide, Bidirectional

PORT B,C,D have 8 bit wide, Bidirectional

PORT E has 3 bit wide, Bidirectional

Ports have 2 control registers

TRISx

PORTx

Pin functionality overloaded with other features

Most pins have 25mA source/sink thus it can drive LEDs directly


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PIC Peripherals: Analogue to Digital Converter

The A/D module has four registers. These registers are: A/D Result High Register (ADRESH)

A/D Result Low Register (ADRESL)

A/D Control Register0 (ADCON0) A/D Control Register1 (ADCON1)

Multiplexed 8 channel inputs Must wait Tacq to charge up sampling capacitor

Can take a reference voltage different from that of the controller


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PIC Peripherals: USART: UART

Serial Communications Peripheral:Universal Synch./Asynch. Receiver/Transmitter

Interrupt on TX buffer empty and RX buffer full

Asynchronous communication: UART (RS-232C serial)

Can do 300bps - 115kbps

8 or 9 bits, parity, start and stop bits, etc.

Outputs 5V so you need a RS232 level converter (e.g.,MAX232)


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PIC Peripherals: Timers

Available in all PICs.

generate interrupts on timer overflow.

Some 8bits, some 16bits, some have prescalers and/or

postscalers

Can use external pins as clock in/clock out

(ie, for counting events or using a different Fosc)

PIC16F877A Block Diagram


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PIC16F877A Block Diagram

InstructionBus

Most

important

register in

the PIC

must be

involved in

all

arithmetic

operations

Data Bus

Data

Memory

Instruction

Memory


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PIC16F877A Instruction Set


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Programming PIC 16F877A

Assembler (MPLAB)

Basic (Pic Basic Pro)

C (HITEC PICC)

Parallel port

Serial port


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PIC Applications

LED FlasherLoop:

bsf PORTB, 0

call Delay_500ms

bcf PORTB, 0

call Delay_500msgoto Loop


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PIC Applications

Button ReadMovlw 0

movwf TRISD, f

bsf TRISD, 2

Loop:

btfsc PORTD, 2

goto light

goto No_light

Light:

bsf PORTB,0

goto Loop

No_light:bcf PORTB,0

goto Loop


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LCDDEFINE OSC 4DEFINE LCD_DREG PORTBDEFINE LCD_DBI T 4DEFINE LCD_RSREG PORTBDEFINE LCD_RSBI T 0DEFINE LCD_EREG PORTBDEFINE LCD_EBI T 1DEFINE LCD_BI TS 4DEFINE LCD_LI NES 2

DEFINE LCD_COMMANDUS 2000DEFINE LCD_DATAUS 50

LCDOUT 254, 1, "MERHABA"LCDOUT 254, 192, "2x16 LCD"

END


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Analog to Digital ConversionFormat: ADCIN Channel,Var

Sample Program:

ABCVAR BYTEADCON1 = 2 ' PORTA is

analog

INPUT PORTA. 0

LOOP:ADCIN PORTA. 0, ABC

LCDOUT 254, 1, #ABC

PAUSE 100

GOTO LOOP


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Pulse Width ModulationFormat:

HPWM Channel,Dutycycle,Frequency

Sample Program:

DEFINE CCP1_REG PORTC'Hpwm 1 pin port

DEFINE CCP1_BI T 2 'Hpwm 1 pin bit

HPWM 1, 64, 1000

' Send a 25% duty cycle PWM signal at

1kHz

END

PIC Microcontroller Introduction

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