Experiment No. 4: External Interrupt

PIC12F683 has got one external interrupt pin (GP2, pin 5) which is edge-triggered:

• rising edge if INTEDG bit in OPTION register is SET,or 
• falling edge if INTEDG bit in OPTION register is CLEAR

In this experiment we are going to simulate an external interrupt event by a tact switch which when pressed gives a falling edge (5->0V) to external interrupt pin. When a valid edge appears on GP2/INT pin, the INTF bit (INTCON<1>) is set. This interrupt can be disabled by clearing INTE control bit (INTCON<4>). While exiting from the Interrupt Service Routine, INTF flag must be cleared to re-enable the interrupt again. ANSEL and CMCON0 must be initialized to configure GPIO as digital I/Os.

On the arrival of an interrupt, the new value of counter will increase by 1 and is displayed as no. of interrupts serviced. 

Experimental Setup:
External interrupt will be simulated by a tact switch on the board. So connect SW1 to GP2 with a jumper wire. For display purpose we will again use a hyperterminal window on a PC.

Software:

   /*

  PIC12F683 Experiment Board

  Experimen No. 4 : External Interrupt

  Date: 06/26/2010

*/

char Message1[] = "Interrupt Demonstration!";

char Message2[] = "Interrupt No.= ";

char *temp = "00", error;

unsigned int i, old_count=0, new_count=0;

// Interrupt Service Routine

void interrupt(void){

    if (INTCON.INTF == 1)          // Check if INTF flag is set

       {

     new_count++;       // If yes, increase counter

     temp[0] = new_count/10 + 48;  // Convert count digits into characters

     temp[1] = new_count%10 + 48;

     INTCON.INTF = 0;       // Clear interrupt flag before exiting ISR

    }

   }

// Main program

void main() {

CMCON0 = 7;

TRISIO = 15;  // GPIO 0, 1, 2, 3 Inputs; Rest are O/Ps

ANSEL = 0;

OPTION_REG = 0x00;       // Clear INTEDG, External Interrupt on falling edge

// Interrupt Setup

    INTCON.INTF = 0;     // Clear interrupt flag prior to enable

    INTCON.INTE = 1;     // enable on change interrupts

    INTCON.GIE  = 1;     // enable Global interrupts

// Define GPIO.3 as UART Rx, and 5 as Tx

error = Soft_UART_Init(&GPIO,3, 5, 9600, 0 );

Delay_ms(100);

do {

 for (i=0; i<= 23; i++) {

      Soft_UART_Write(Message1[i]);

      Delay_ms(50);

     }

  Soft_UART_Write(10); // Line Feed

  Soft_UART_Write(13); // Carriage Return

  delay_ms(500);

 if (new_count > old_count)

       {

     for (i=0; i<= 13; i++) {

      Soft_UART_Write(Message2[i]);

      Delay_ms(50);

     }

     for (i=0; i<= 1; i++) {

      Soft_UART_Write(temp[i]);

      Delay_ms(50);

     }

  Soft_UART_Write(10); // Line Feed

  Soft_UART_Write(13); // Carriage Return

  old_count=new_count;

     }

 } while(1);

}

Experimental Output:
On hyperterminal window, you will continuously see a message "Interrupt Demonstration!". When you press the tact switch, that will give an interrupt (falling edge), and the counter value goes up by 1. The updated counter value will be displayed.