Day 2 AM Interrupts

7/30/2019 Day 2 AM Interrupts

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20-Aug-2010 Paranz 1

Introduction to PICMicrocontroller Programming

& Interfacing

August 19-21, 2010Franz Duran


Interrupts

DAY 2 Morning Session

August 20, 2010


OVERVIEW

Interrupt BasicsInterrupt sources

Interrupt service routine (ISR)

Interrupts in PIC16F84A, PIC16F877A

Associated SFRs

RB0 Interrupt

PORTB Interrupt on-change


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BASICS OF INTERRUPTS

Very important microcontroller featureAllows internal & external events to

trigger an interruptnotify the CPU

CPU temporarily halt program

execution and respond to the interruptExecute an interrupt service routine



void main()

{

InitializeSystem();

while(1)

{

Task1();

Task2();

Task3();

Task4();

Task5();

}

}

void interrupt isr(void)

{

//Execute relevant instructions.

//Clear interrupt flag.

}

an interrupt is tri ggered

- CPU saves context (Program Counter, STATUS, W)

CPU exits from interrupt

service routine; previouscontext is restored, continue

program execution.

CPU executes theinterrupt service routine


INTERRUPTS: PIC16F84A

4 Interrupt sourcesRB0 interrupt

PORTB-on-change interruptTMR0 interrupt

Data EEPROM Write Complete Interrupt

SFR: INTCON


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15 interrupt sourcesRB0 interrupt

PORTB-on-change interrupt

TMR0 interrupt

Data EEPROMWrite Complete Interrupt

UART TX, UART RX

ADC, TMR1, TMR2

SSP, CCP, etc..

SFRs: INTCON, PIR1, PIR2, PIE1, PIE2


INTERRUPTS: INTCON

PIC16F84A

PIC16F877A



Interrupt Logic


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Interrupt Logic


RB0/INT INTERRUPT

RB0 pin is an interrupt source

Generate an interrupt on the ff. event:falling-edge signal transition

+5v 0v

rising-edge signal transition

0v +5v


RB0/INT INTERRUPT

1 interrupt on rising edge

0 interrupt on falling edge

Set automatically by hardwareon interrupt; cleared via software

Set to enableRB0/INT interrupt

Set to enable interrupt


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RB0/INT INTERRUPT

1

1

01

ISR is executed


RB0/INT INTERRUPT#include

__CONFIG(HS & WDTDIS & LVPDIS & PWRTDIS & UNPROTECT);

void main()

{

//Button at RB0.

INTEDG = 0; //Interrupt on falling edge.

INTF = 0; //Clear RB0 interrupt flag.

INTE = 1; //Enable RB0 interrupt.

GIE = 1; //Enable interrupt.

TRISC1 = 0; //LED at RC1

RC1 = 0;

while(1); //Do nothing but wait for RB0 interrupt,

// to occur then execute the ISR.

}

Example#1


RB0/INT INTERRUPT

//Interrupt Service Routine

void interrupt isr_RB0(void)

{

RC1 = 1; //Toggle LED.INTF = 0; //Clear RB0 interrupt flag.

}

Example#1


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RB0/INT INTERRUPTEXERCISE:

Change to INTEDG=1 rising edge

Observe behaviour


RB0/INT INTERRUPT

EXERCISE:Modify Example#1

Toggle another LED in program loopLED1 toggled when RB0/INT triggers

LED2 blink in program loop

toggle LED2 every 500 msec

use delay.c and delay.h

Example#2



Other interrupt INFOs:GIE is automatically cleared during ISR

execution; GIE is set on ISR exit

prevent the ISR from being interrupted

Interrupt latency time between interrupt & execution of ISR

CPU complete current instruction, do context save

3-4 instruction cycles for external interrupts

2-3 instruction cycles for internal interrupts


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other INFOs: (cont)ISR should be as short as possible set event flags inside the ISR &

do associated tasks in program loop



__CONFIG(HS & WDTDIS & PWRTDIS & UNPROTECT & LVPDIS);

#define LED RC1

#define TRUE 1

#define FALSE 0

#define TOGGLE 1

volatile bit rb0_int_flag = FALSE; //event flag variable

void interrupt ISR(void)

{

rb0_int_flag = TRUE;

INTF = 0; //clear RB0 interrupt flag

}

Example#3


RB0/INT INTERRUPT

void main()

{

InitSystem();

while(1){

if(rb0_int_flag == TRUE) //Poll flag.

{

rb0_int_flag = FALSE; //Clear flag.

LED = 1; //Do task.

}

}

}

Example#3


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other INFOs: (cont)ISR should be as short as possible set event flags inside the ISR &

do associated task in program loop

Global variables modified inside the ISR AND

program loop should be declared asvolatile



volatile keyword

Variable type qualifier

inform the compiler that the value of a

variable may be modified by the hardware inways that are not explicitly specified duringnormal program operation.

Compiler should not optimize the variable inmain (or in other functions)



void main()

{

INTEDG = 0; //Falling edge


INTE = 0; //Disable RB0 interrupt.

GIE = 0; //Disable all interrupt.

TRISC1 = 0; //LED

RC1 = 0;

while(1)

{

if(INTF==1) //poll INTF if it is set

{

RC1 = 1; // then toggle LED.


}

}

}

Example#4


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PORTB INTERRUPT ON CHANGE

PORTB pins can be configuredas an interrupt source

Generate an interrupt

when the logic signal

level on any pin

changes



Generate an interrupt on both risingedgeand falling edge

Operation:old value of PORTB during last read is

stored

if current value not equal to old value,

mismatch condition

RBIF=1



1

1

01ISR is executed


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To clear PORTB interrupt:read value of PORTB AND

clear RBIF



Set by hardware automaticallyon interrupt; cleared via software

Set to enablePORTB interrupt

Set to enableinterrupt


PORTB INTERRUPT ON CHANGE#include


{

unsigned char portb_temp;

RC1 = 1; //Toggle LED

portb_temp = PORTB & 0xF0; //Read to clear mismatch

RBIF = 0; //Clear interrupt flag

}

void main()

{

TRISB = 0b00010000; //RB4 is input, rest are output & unused.

RBIF = 0; //Clear interrupt flag.

RBIE = 1; //Enable interrupt.

GIE = 1; //Enable all (global) interrupt.

TRISC1 = 0; //LED

RC1 = 0;

while(1); //do nothing, simply wait for ISR

}

The ISR is

executed twice

during a buttonpress

Example#5


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PORTB INTERRUPT ON CHANGE If using multiple PORTB pins, use switch() and masks

Example: RB4 and RB5 are interrupt source


{


portb_temp = PORTB & 0b00110000; //read PORTB

switch(portb_temp)

{

case 0b00100000: //if Pushbutton1 is pressed,

LED1 = TOGGLE; //toggle LED1

break;

case 0b00010000: //if Pushbutton2 is pressed,

LED2 ^= TOGGLE; //toggle LED2

break;

}

RBIF = 0; //clear interrupt flag

}


Multiple Interrupts

PIC16F has several interrupts

But only one ISR

If using multiple interrupts:Poll the interrupt enable bit and interrupt flag

bit

Example: RB0 int & PORTB Int.Poll INTE and INTF

Poll RBIE and RBIF


Multiple Interruptsvoid interrupt isr(void)

{


//Check if PORTB Int. triggered the interrupt

if(RBIE && RBIF)

{

//codes here

RBIF = 0; //clear interrupt flag

}

//Check if RB0 triggered the interrupt

if(INTE && INTF)

{

//codes here

INTF = 0; //clear interrupt flag

}

}


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Multiple Interrupts

EXERCISE: using multiple interruptsToggle LED1 with RB0 interrupt

Toggle LED2 and LED3 with PORTB interrupt

Toggle LED2 with RB4

Toggle LED3 with RB5



other INFOs: (cont)ISR should be as short as possible

Global variables modified inside the ISR AND

program loop should be declared asvolatile

interrupt flags are set even if interrupt isdisabled INTF is set by hardware, even if INTE=0 & GIE=0


INTERRUPTS: Summary

Interrupts expands MCU functionality

Main benefit:speed of response to internal/external events max. 4 TOSC interrupt latency

reduced software overhead

program efficiency greatly increased

facilitates multitasking

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Day 2 AM Interrupts