pic microcontrollers pic16f877a -...

PIC Microcontrollers PIC16F877a

A.Suyampulingam

Assistant Professor(Sr.Gr)

Introduction

What is PIC?

• A family of Harvard architecture microcontrollers made by Microchip Technology.

• Micro Controller : Micro Processor + Peripherals

• Derived from the PIC1650 originally developed by General Instrument Microelectronics Division.

• The name PIC was originally an acronym for "Programmable Intelligent Computer".

• The name PIC is referred to Peripheral Interface Controller.

• It shares some common features with RISC designs.

Introduction

Why PIC is popular? low cost ,wide availability with high clock speed of low cost or free development tools Only 35 instructions to remember serial programming and re-programming with flash memory capability Its code is extremely efficient, allowing the PIC to run with typically less program memory than its larger competitors PIC is very small and easy to implement for non-complex

problems and usually accompanies to the microprocessors as an interface

Two Different Architectures

Harvard Architectures

(newer arch.)

Von-Neumann Architecture

Two Different Architectures

Harvard Architectures

• Used mostly in RISC CPUs • Separate program bus and

data bus: 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

and memory • RAM and program memory

share the same bus and the same memory, and so must have the same bit width

• Bottleneck: Getting instructions interferes with accessing RAM

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

Classification of PIC Microcontrollers

• Based on instruction word length Base-Line or low end Architectures: 12-bit Instruction Word

length (PIC10FXX,PIC12C5XX,PIC16C5X)

Mid-Range Architectures : 14-bit Instruction Word length

(PIC16C6X,PIC16C7XX,PIC16F877X)

High-End Architectures : 16-bit Instruction Word length

(PIC17C4x,PIC17C7xx,PIC18Cxxx, PIC18F452)

Classification of PIC Microcontrollers

• Based on data length

8 bit microcontroller (PIC1612F,PIC17F,PIC16F877)

16 bit microcontroller(dsPIC30F,dsPIC33F, PIC24FX,PIC24H)

32 bit microcontroller(PIC32FXX,PIC32MX)

The PIC Family: Speed

12C50X 4MHz

12C67X 10MHz

16F877 20MHz

17C4X/17C7XXX 33MHz

18CXXX 40MHz

• Can use crystals, clock oscillators, or even an RC circuit.

• Some PICs have a built in 4MHz RC clock, Not very accurate, but requires no external components!

• Instruction speed = 1/4 clock speed (Tcyc = 4 * Tclk)

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

Clock and Instruction Cycles

Instruction 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.

The PIC Family: Program Memory

• Technology: EPROM, FLASH, or ROM

• It varies in size from one chip to another.

12C508 512 12bit instructions

16C711 1024 (1k) 14bit instructions

16F877 8192 (8k) 14bit instructions

17C766 16384 (16k) 16bit instructions

PIC16F877A Features

• High Performance RISC CPU:

Only 35 single word instructions to learn

Operating speed: DC - 20 MHz clock input DC - 200 ns instruction cycle

All single cycle instructions except for program branches, which are two-cycle

PIC Memory

• The PIC16F877A has an 8192 (8k) 14bit instruction program memory

• 368 Bytes Registers as Data Memory :

– Special Function Registers: used to control peripherals and PIC behaviors

– General Purpose Registers: used to a normal temporary storage space (RAM)

• 256 Bytes of nonvolatile EEPROM

Peripheral Features

• Timer0: 8-bit timer/counter with 8-bit prescaler

• Timer1: 16-bit timer/counter with prescaler,can be incremented during Sleep via external crystal/clock

• Timer2: 8-bit timer/counter with 8-bit period register, prescaler and postscaler

• Two Capture, Compare, PWM modules

• Capture is 16-bit, max. resolution is 12.5 ns

• Compare is 16-bit, max. resolution is 200 ns

• PWM max. resolution is 10-bit

• 10-bit, up to 8-channel Analog-to-Digital Converter (A/D)

• Synchronous Serial Port (SSP) with SPI™(Master mode) and I2C™ (Master/Slave)

• Universal Synchronous Asynchronous Receiver,Transmitter (USART/SCI) with 9-bit address detection

• Parallel Slave Port (PSP) – 8 bits wide with external RD, WR and CS controls

• Brown-out detection circuitry for Brown-out Reset (BOR)

Peripheral Features

– 5 Digital I/O Ports

– Three timer/counter modules

• Timer0: 8-bit timer/counter with 8-bit pre-scaler

• Timer1: 16-bit timer/counter with pre-scaler, can be incremented during SLEEP via external crystal/clock

• Timer2: 8-bit timer/counter with 8-bit period register, pre-scaler and post-scaler

– A 10-bit ADC with 8 inputs

– Two Capture, Compare, PWM modules

• Capture is 16-bit, max. resolution is 12.5 ns

• Compare is 16-bit, max. resolution is 200 ns

• PWM max. resolution is 10-bit

– Synchronous Serial Port (SSP) with SPI™ (Master mode) and I2C™ (Master/Slave)

– Universal Synchronous Asynchronous Receiver Transmitter (USART/SCI) with 9-bit address detection

– Parallel Slave Port (PSP) 8-bits wide, with external RD, WR and CS controls

PIC16F877 pin-out

The microcontroller pins have multiple functions

PIC microcontroller Family

MCU

Pins

Data

word

(bits)

Program

memory

(bytes)

Typical

Instruction

Set

Speed

MIPS

Comment

10FXXX

= 6

8

<= 512

33 x 12

bits

<= 2

Low pin count, small form factor,

cheap

No EEPROM, none low power,

assembler program

12FXXX

= 8

8

<= 2 KB

12 / 14 bits

<= 5

Low pin count, small form factor,

cheap

EEPROM, 10-bit ADC, some low

power, assembler

16FXXX

<= 64

8

<= 14 KB

35 x 14

bits

<= 5

Mid-range, UART, I2C, SPI

many low power, C or assembler

program

18FXXXX

<=

100

8

<= 128 KB

75 x 16

bits

<= 16

High range, CAN, USB

J series 3V supply, C program

24FXXXX

<=

100

16

<= 128 KB

76 x 24

bits

= 16

Power range, 3V supply, no

EEPROM,

data RAM < 8 KB, C program

PIC16F877a Architecture

PIC Program Memory

PIC16F877a Data Memory

Direct/Indirect Addressing

PIC Family Control Registers

Uses a series of “Special Function Registers” for controlling peripherals and PIC behaviors. STATUS Bank select bits, ALU bits (zero, borrow, carry)

INTCON Interrupt control: interrupt enables, flags, etc.

OPTION_REG contains various control bits to configure the TMR0 prescaler/WDT postscaler ,the External INT Interrupt, TMR0 and the weak pull-ups on PORTB

Special Function Register STATUS Register

SFR-INTCON Register

PIC Peripherals

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

• Different PICs have different on-board peripherals

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 sets whether each pin is an input (1) or output (0) – PORTx sets their output bit levels or contain their input bit levels

• Pin functionality “overloaded” with other features • Most pins have 25mA source/sink thus it can drive LEDs directly

PIC16F877A Pin Layout

PORTA PORTB

PORTC PORTC

PORTD

PORTD

Interrupts sources in the PIC 16F877 Interrupt Source

Interrupt trigger event

CCS C Interrupt label

TIMERS

Timer 0

Timer 0 register overflow

INT_TIMER0

Timer 1


INT_TIMER1

CCP 1

Timer 1 capture or compare detected

INT_CCP1

Timer 2


INT_TIMER2

CCP2

Timer 2 capture or compare detected

INT_CCP2

PORTS

RB0/INT pin

Change on single pin RB0

INT_EXT

Port B pins

Change on any of four pins RB4 – RB7

INT_RB

Parallel Slave Port

Data received at PSP (write input active)

INT_PSP

Analog Converter

A/D conversion completed

INT_AD

Analog Comparator

Voltage compare true

INT_COMP

SERIAL

UART Serial Port

Received data available

INT_RDA

UART Serial Port

Transmit data buffer empty

INT_TBE

SPI Serial Port

Data transfer completed (read or write)

INT_SSP

I2C Serial Port

Interface activity detected

INT_SSP

I2C Serial Port

Bus collision detected

INT_BUSCOL

MEMORY

EEPROM

Non-volatile data memory write complete

INT_EEPROM

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)

Timer Interrupt Process

Program Execution

Program Execution

1

Start counter

statement

2

Run

Counter

until

overflow

5

Time-out

Process

(Interrupt

Service

Routine)

7

Continue

3

Timeout

Interrupt

6

Return

from

Interrupt

Time-out forces the program to be suspended and the ISR executed

Timer0 features

• 8-bit timer/counter

• Readable and writable

• 8-bit software programmable prescaler

• Internal or external clock select

• Interrupt on overflow from FFh to 00h

• Edge select for external clock

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