PIC Interupts

8/10/2019 PIC Interupts

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InterruptsInterrupts

IntroductionIntroduction

Interrupts in the PIC16F877AInterrupts in the PIC16F877A

Setting up the InterruptsSetting up the Interrupts Using the InterruptsUsing the Interrupts

SummarySummary


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IntroductionIntroduction

An interrupt is a specific event that causes the normal programexecution to be suspended wherever it is and an interrupt function isexecuted.

Interrupts increases the program efficiency by allowing externaldevices or internal events to force a change in the executionsequence.

When an interrupt signal is received, the current instruction iscompleted and the address of the next instruction (the returnaddress) is pushed into the first available stack location.

Then the program jumps to program address 004, and continuesfrom there until it sees a Return From Interrupt (RETFIE) instruction.

When the interrupt function ends, the return address is pulled fromthe stack. Program execution then restarts at the original location.

Normal program execution continues when the interrupt functionreturns.

The PIC16F877A has a number of interrupt sources such as a timeroverflow, an incomingRS-232 character or a change on a pin.


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The primary interrupt sources for PIC16F877AThe primary interrupt sources for PIC16F877Aare Timers and Port Bare Timers and Port B

The overflow of the Timers triggers the interruptThe overflow of the Timers triggers the interrupt

RB0/INT is an external interrupt input pin and isconfigured using the INTEDG bit(OPTION_REG)

Pins B4-B7 can be set up so that any change onPins B4-B7 can be set up so that any change onthese inputs initiates the interrupt (these inputs initiates the interrupt (interrupt on-

change feature) This could be used to detect when a button on a

keypad connected to Port B has been pressed


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Setting up the InterruptsSetting up the Interrupts


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The Interrupt Control register (INTCON) records

individual interrupt requests in flag bits.

It also has individual and global interrupt enable bits.

INTCON contains various enable and flag bits for

the TMR0 register overflow, RB port change and

external RB0/INT pin interrupts.

INTEDG

is Interrupt Edge Select bit If set to 1 : Interrupt on rising edge of RB0/INT pin

If set to 0 : Interrupt on falling edge of RB0/INT pin


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Interrupt flag bits are set when an interrupt condition

occurs regardless of the state of its corresponding

enable bit or the global enable bit, GIE (INTCON).

User software should ensure the appropriate interruptflag bits are clear prior to enabling an interrupt.

When bit GIEis enabled and an interrupts flag

bit and mask bit are set, the interrupt will vector

immediately.

The GIEbit is cleared on Reset.


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The PIE1 register contains the individual

enable bits for the peripheral interrupts.

The peripheral interrupt sources are fromADC, Timer and Serial I/O

Bit PEIE (INTCON) must be set to

enable any peripheral interrupt.


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The PIR1 register contains the individual

flag bits for the peripheral interrupts.

Interrupt flag bits are set when an interruptcondition occurs regardless of the state of

its corresponding enable bit or the global

enable bit, GIE (INTCON). User software should ensure the

appropriate interrupt bits are clear prior to

enabling an interrupt.


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The bits in the PIR1 register

ADIF: A/D Converter Interrupt Flag bit

1 = An A/D conversion completed

0 = The A/D conversion is not complete TMR2IF: TMR2 to PR2 Match Interrupt Flag bit

1 = TMR2 to PR2 match occurred (must be cleared in

software)

0 = No TMR2 to PR2 match occurred TMR1IF: TMR1 Overflow Interrupt Flag bit

1 = TMR1 register overflowed (must be cleared in software)

0 = TMR1 register did not overflow


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The PIE2 register contains the individual

enable bits for the CCP2 peripheral

interrupt, the SSP bus collision interrupt,EEPROM write operation interrupt and the

comparator interrupt.


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The PIR2 register contains the flag bits for the

CCP2 interrupt, the SSP bus collision interrupt,

EEPROM write operation interrupt and the

comparator interrupt The peripheral interrupt flags are contained in the

Special Function Registers, PIR1 and PIR2.

The corresponding interrupt enable bits are

contained in Special Function Registers, PIE1 and

PIE2, and the peripheral interrupt enable bit is

contained in Special Function Register, INTCON


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When an interrupt is responded to, the GIE bit is cleared to

disable any further interrupt, the return address is pushed

onto the stack and the Program Counter (PC) is loaded with

0004h.

Once in the Interrupt Service Routine, the source(s) of the

interrupt can be determined by polling the interrupt flag bits.

The interrupt flag bit(s) must be cleared in software before re-

enabling interrupts to avoid recursive interrupts.

For external interrupt events, such as the INT pin or PORTBchange interrupt, the interrupt latency will be three or four

instruction cycles.


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By default, all the interrupts in the PIC16F877ABy default, all the interrupts in the PIC16F877A

are disabledare disabled

The interrupts can be enabled byThe interrupts can be enabled by

GIE=1; // Global interrupt enable

The interrupts can be disabled byThe interrupts can be disabled by

GIE=0; // Global interrupt disable

Individual interrupts can be enabled separately asIndividual interrupts can be enabled separately aswellwell

For example,For example, INTE=1; enables the externalenables the external

interrupt input from Pin RB0interrupt input from Pin RB0


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Using the InterruptsUsing the Interrupts

INT INTERRUPT

External interrupt on the RB0/INT pin is edge triggered, eitherrising if bit INTEDG (OPTION_REG) is set or falling if theINTEDG bit is clear.

When a valid edge appears on the RB0/INT pin, flag bit, INTF

(INTCON), is set. This interrupt can be disabled by clearing enable bit, INTE

(INTCON).

Flag bit INTF must be cleared in software in the InterruptService Routine before re-enabling this interrupt.

The INT interrupt can wake-up the processor from Sleep if bitINTE was set prior to going into Sleep.

The status of global interrupt enable bit, GIE, decides whetheror not the processor branches to the interrupt vector followingwake-up.


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TMR0 INTERRUPT

An overflow (FFh 00h) in the TMR0

register will set flag bit, TMR0IF

(INTCON).

The interrupt can be enabled/disabled by

setting/clearing enable bit, TMR0IE

(INTCON).


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The interrupt function is designated by preceding it withinterrupt.

In the interrupt service routine functions can be specified bypreceding each with the proper name like RBIFfor the Port Bchange interrupt (RB4-B7)

An interrupt must be specifically enabled (For exampleRBIE=1for enabling Port B change interrupt) and interruptsmust be globally enabled (GIE=1). The GLOBALenable/disable controls whether any interrupts are serviced.

If interrupts are disabled and an interrupt event happens, thenthe interrupt function will be called when interrupts areenabled. If multiple interrupt events of the same type happenwhile interrupts are disabled, then the interrupt function iscalled only once when interrupts are enabled.


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In the case of Timer Interrupts,In the case of Timer Interrupts, interrupts aredisabled before the timer is read and combinedwith the overflow count.

This is done to prevent the following situation:

The timer value is read and it is 65535 The overflow interrupt happens and the counter

is incremented to 1

The program continues and reads the counter

as 1 The time is an assumed to be 65536+65535

when in fact the correct time is 65535


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An example (Using RB interrupts, continues on next slide):An example (Using RB interrupts, continues on next slide):#include

#include

#define _XTAL_FREQ 20000000 // Set the oscillator frequency to 20MHz

int i=0;

int j=0;

//---Function Definition-----//--Interrupt Service function--

interrupt ISR (void) // Interrupt function definition

{ if (RBIF) // If the RB change flag is 1, do .....

{ RBIE=0; //Disable RB change interrupt

{ while (!RB7); //Detect Pin B7 to be logic low (Falling Edge)

__delay_ms(100);

PORTC=j;

j++;

}RBIF=0; // Reset the external interrupt flag

RBIE=1; // RE-Enable RB change interrupt

}

GIE=1; //Enable Global Interrupt

}


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An example (Using RB interrupts, continued from previous slide):An example (Using RB interrupts, continued from previous slide):

//--Main Funtion --

void main(void)

{ ADCON1 = 0b00000111; //Set Port A as digital I/O

TRISA=0xFF; // Ser PORT A as an OUTPUT

TRISB=0xF0; // Set PORT B as an IN/OUTPUT

nRBPU=0; //Enable Port B Internal Pull Up ResistorsTRISC=0; // Set PORT C as an OUTPUT

PORTC=0; // Set the value of PORT C to 0

INTE=1; // Enable external interrupts from RB0

RBIE=1; //Enable the RB port change interrupt


RBIF=0; //Clear RB port change interrupt flag

while(1) //Keeps running{ PORTB++;// Increase the PORT B value by 1.

for(i=0;i


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In this example, the RB interrupt is used

The input of pins B4 to B7 are monitoredusing this interrupt

Falling edge will trigger the interrupt

A falling edge at pin B7 will increase thecounter which output to Port C (Can be 8

LEDs or BCD 7 segment) And now construct the circuit for this

program


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Another example (Using Timer1 interrupts, continues on next slide):Another example (Using Timer1 interrupts, continues on next slide):#include #include


char count1=0, count2=0;

//--Interrupt Service function--interrupt ISR(void) // Interrupt function definition

{ if (TMR1IF) // If the TMR1 Overflow flag is 1, do .....

{ TMR1IE=0; // TMR1 Overflow Interrupt Disable

TMR1ON=0; //Turn off Timer 1

RB0=!RB0; //Blinking the LED RB0

TMR1L=count1; //Change the counter values for Timer1

TMR1H=count2; //Change the counter values for Timer1

TMR1IF=0; // Reset the TMR1 Overflow interrupt flag

TMR1IE=1; // TMR1 Overflow Interrupt Enable

TMR1ON=1; //Turn on Timer 1

}

GIE=1; //Enable back the global interrupt inputs, if not interrupt only happens for once! HahA!

}


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Another example (Using Timer1 interrupt to generate pulse,Another example (Using Timer1 interrupt to generate pulse,continued from previous slide and continues on next slide):continued from previous slide and continues on next slide):

void main (void) //--Main Funtion --

{ unsigned int reading=0;

TRISA=0xFF; // Ser PORT A as an INPUT

TRISB=0xF0; // Set PORT B as an IN/OUTPUTnRBPU=0;

ADCON1=0b01001110; //Set ADFM (bit 7 of ADCON1) to 0 for left justified

//Only RA0 is selected as analog input

ADCON0=0b11000001;

T1CKPS1 = 0; /* Prescaler of 1 */


TMR1CS = 0; /* Select internal Clock source */

TMR1ON = 1; /* Enable timer1 */


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Another example (Using Timer1 interrupts, continued from previous slide):Another example (Using Timer1 interrupts, continued from previous slide):

TMR1IE = 1; /* Enable timer1 interrupts */

TMR1L = 0x00; /* Low byte */

TMR1H = 0x00; /* High byte */


TMR1IF=0; //Clear TMR1 interrupt flagPEIE=1; //Peripheral Interrupt Enable

while (1)

{ __delay_ms(100);

ADCON0=ADCON0|1;

GO = 1; //Start A/D Conversion

while(GO==1); //Wait end of conversion (conversion complete)

reading = (65535-ADRESH*255); //Start A/D conversion and read the datacount1 = reading%256 ;

count2 = reading/256.0;

}

}


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In this example, the Timer1 interrupt is used

The interrupt will be triggered when Timer1 overflows

Each time the Timer1 interrupt is triggered, the LED atPin RB0 will change the lighting pattern

The counter values for Timer1 is changed according tothe reading from ADC

So the input from ADC will affect the speed of the LEDblinking

And now construct the circuit for this program Dont forget, enable the Peripheral Interrupt Enable bit

(PEIE, bit 7 of INTCON register) if you want to useinterrupt from Timers (1&2)


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Another example (Using Timer0 interrupt to generate pulse, continues onAnother example (Using Timer0 interrupt to generate pulse, continues onnext slide):next slide):

#include

#include


char count1=0, count2=0;

//--Interrupt Service function--

interrupt ISR(void) // Interrupt function definition




if (count2++%2)

TMR0=count1; //Change the counter values for Timer0else

TMR0=255-count1; //Change the counter values for Timer0



}

GIE=1;

}


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Another example (Using Timer0 interrupt to generate pulse,Another example (Using Timer0 interrupt to generate pulse,continued from previous slide and continues on next slide):continued from previous slide and continues on next slide):

//--Main Funtion --

void main(void)

{ TRISA=0xFF; // Ser PORT A as an INPUT

TRISB=0xF0; // Set PORT B as an IN/OUTPUT

ADCON1=0b01001110; //Set ADFM (bit 7 of ADCON1) to 0 for left justified

//Only RA0 is selected as analog input

ADCON0=0b11000001;

T0CS = 0; /* Select internal Clock source */

PSA = 0; /* Prescaler is assigned to the Timer0 module */PS2 = 1;

PS1 = 1;

PS0 = 0; /* Set prescaler rate to 1:128 */


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Another example (Using Timer0 interrupt toAnother example (Using Timer0 interrupt togenerate pulse, continued from previous slide):generate pulse, continued from previous slide):


TMR0 = 0x00; /* Timer0 Counter */

GIE=1; // Global interrupt enableTMR0IF=0; //Clear TMR1 interrupt flag

PEIE=1; //Peripheral Interrupt Enable

while (1)

{ __delay_ms(100);

ADCON0=ADCON0|1;

GO = 1; //Start A/D Conversion

while(GO==1); //Wait end of conversion (conversion complete)count1 = 255-ADRESH; //Start A/D conversion and read the data

}

}

//End of program


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In this example, the Timer0 interrupt is used forgenerating a pulse with varying pulse width


Each time the Timer0 interrupt is triggered, the LED at

Pin RB0 will turn on and off alternately The pulse width is changed according to the reading

from ADC

So the input from ADC will affect the ON time of the LED

Tap the pin of RB0 to an oscilloscope to check thewaveform

And now construct the circuit for this program


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Another example (Using Timer2 interrupt to generate pulse, continues onAnother example (Using Timer2 interrupt to generate pulse, continues onnext slide):next slide):

#include

#include


//--Interrupt Service function--

interrupt ISR(void) // Interrupt function definition




TMR2IF=0; // Reset the TMR2 Overflow interrupt flagTMR2IE=1; // TMR2 Overflow Interrupt Enable

}

GIE=1;

}


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Another example (Using Timer2 interrupt to generate pulse, continued from previousAnother example (Using Timer2 interrupt to generate pulse, continued from previousslide):slide):

//--Main Funtion --

void main(void)

{ TRISC=0x00; //Port C as outputs

TRISB=0x00; //Port B as outputs

T2CON = 0b00001001; // Timer 2 control register

//TOUTPS3:TOUTPS0: Timer2 Output Postscale Select to 1:2//T2CKPS1:T2CKPS0: Timer2 Clock Prescale Select to 4


PR2 = 0xA0; /* Timer0 Counter */


TMR2IF=0; //Clear TMR1 interrupt flag

TMR2ON=1; //Turn on Timer 2


while (1); //Run Run Run!

}

//End of Program


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The previous example is modified to use the Timer2 interrupt forgenerating a pulse


Each time the Timer2 interrupt is triggered, the LED at Pin RB2 willturn on and off alternately (Toggling)

The Timer2 Control Register, T2CONsets Timer 2 with pre-scaler of4, counting from 0 to A0h, post-scaler is 2, so every 2 times Timer 2overflows, an interrupt is generated

If the clock frequency is 20MHz, the instruction clock frequency is5MHz (divide by 4)

Instruction clock period is 0.2 s, the time taken for Timer 2 tooverflow = 160 x 4 x 2 x 0.2 = 256 s

Tap the pin RB2 to an oscilloscope to check the waveform


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Using the Interrupts (Output toUsing the Interrupts (Output to

Virtual Terminal)Virtual Terminal) Do this example (Continues on next slide):Do this example (Continues on next slide):#include #include

#include

#include

#define _XTAL_FREQ 20000000

#define PUSH_BUTTON RB6

long int overflow_count;

void init_rs232()

{ BRGH = 1;

SPBRG = 129; // set baud rate: Fosc=20Mhz, BR=9600

TX9 = 0; // ninebits?1:0,,,8- or 9-bit transmission

SYNC = 0; // asynchronous

SPEN = 1; // enable serial port pins

TXEN = 1; // enable the transmitter & (automatically)TXIF=1

CREN = 1; // enable receptionSREN = 0; // no effect

TXIE = 0; // disable tx interrupts

RCIE = 0; // disable rx interrupts

}


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Virtual Terminal)Virtual Terminal) Do this example (Continues from previous slide):Do this example (Continues from previous slide):interrupt ISR(void) // Interrupt function definition{ if (TMR1IF) // If the TMR1 Overflow flag is 1, do .....


overflow_count++;



}

GIE=1;

}

void main( )

{ unsigned long int time ; //32 bit integer data

init_rs232();

TRISB=0xF0; // Set PORT B as an IN/OUTPUTnRBPU=0;



TMR1CS = 0; /* Select internal Clock source */

TMR1ON = 1; /* Enable timer1 */


TMR1L = 0x00; /* Low byte */

TMR1H = 0x00; /* High byte */


TMR1IF=0; //Clear TMR1 interrupt flag


while(1){ while(PUSH_BUTTON);// Wait for press

TMR1H=0;

TMR1L=0;

overflow_count=0;

while(!PUSH_BUTTON);//Wait for release

GIE=0; //Disable all interrupts

time = TMR1H*256+TMR1L;

time = time + (overflow_count


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Virtual Terminal)Virtual Terminal)

In this example, the timer 1 overflow interrupt will

be used to extend the timer 1 timer from 16 bits

to 32 bits by counting the number of times the

timer overflows. When running the program, press the button and

release, the time it was held down is shown to 6

decimal places in the Monitor panel.

The %06lu format specifier is the same as %6lu

except leading zeros are printed.


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Virtual Terminal)Virtual Terminal)

The formula time/5000000in this printf("Time is %lu.%06lu seconds.\r\n",time/5000000, (time/5)%1000000);

Clock frequency is 20MHz, so instructionclock frequency is 5MHz = 5000000 Hz

The timer value will increase by one, eachand everytime the instruction clock

complete a cycle so the time to take for the timer value toproduce N cycles will become N/5000000


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SummarySummary

An interrupt causes the normal programexecution to be suspended and an interruptfunction is executed.Normal program executioncontinues when the interrupt function returns.

The PIC16F877A has a number of interruptsources such as a timer overflow, an incomingRS-232 character or a change on a pin (Port B4-B7).

Interrupts are disabled by default.Interrupts are disabled by default.

They must be enabled before being usedThey must be enabled before being used


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