ProjectBandya

AVR C Programming of External Interrupt

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This AVR tutorial looks at how to use the external interrupt of an ATMega8515 microcontroller by completing the task that is describe below. Before continuing with this tutorial it is highly recommended that you go through the tutorial on the AVR 8-bits Microcontroller External Interrupts.


The figure below shows a circuit diagram in which eight (8) LEDs are connected to port C of an ATMega8515 AVR microcontroller. Also there is a push button switch connected between ground and the External Interrupt 0 (INT0)pin (pin 31) of the ATMega8515.


The Task
The task is to write a C program, utilizing the external interrupt of the ATMega8515, that when download to the ATMega8515 in the figure below perform one (1) of two (2) operations. On start-up OPERATION 1 is is executed and continue indefinitely. If the push-button switch is pressed OPERATION 1 is paused and OPERATION 2 is carried out after which OPERATION 1 is resumed.


OPERATION 1 - A roll action is perform using the LEDs. The first LED is lit and roll down to the last LED then back to the first LED. This operation is done continuous.


OPERATION 2 - ALL the LEDs blink five (5) times.


Important: The internal oscillator for the microcontroller must be enabled for the circuit to operate as described. Otherwise the circuit must be modified to include an external oscillator/crystal to clock the microcontroller.

/*
 *  Written in AVR Studio 5 / AVR Studio 6
 *  Compiler: AVR GNU C Compiler (GCC)
 *
 *  Author: AVR 
 *  Website: www.projectbandya.com

*/
 
#include <avr/io.h>
#include <avr/interrupt.h>
 
#define F_CPU 4000000UL
#include <util/delay.h>
 
#define DataPort PORTC // Using PortC as our Dataport
#define DataDDR  DDRC
 
//Interrupt Service Routine for INT0
ISR(INT0_vect)
{
 unsigned char i, temp;
 
 _delay_ms(500); // Software debouncing control
 
 temp = DataPort; // Save current value on DataPort
 
 /* This for loop blink LEDs on Dataport 5 times*/
 for(i = 0; i<5; i++)
 {
  DataPort = 0x00;
  _delay_ms(500); // Wait 5 seconds
  DataPort = 0xFF;
  _delay_ms(500); // Wait 5 seconds
 }
 
 DataPort = temp; //Restore old value to DataPort 
} 
 
int main(void)
{
 DDRD = 1<<PD2;  // Set PD2 as input (Using for interupt INT0)
 PORTD = 1<<PD2;  // Enable PD2 pull-up resistor
 
 DataDDR = 0xFF;  // Configure Dataport as output
 DataPort = 0x01; // Initialise Dataport to 1
 
 GICR = 1<<INT0;     // Enable INT0
 MCUCR = 1<<ISC01 | 1<<ISC00; // Trigger INT0 on rising edge
 
 sei();    //Enable Global Interrupt
 
    while(1)
    {
  if(DataPort >= 0x80)
   DataPort = 1;
  else
   DataPort = DataPort << 1; // Shift to the left
 
  _delay_ms(500); // Wait 5 seconds
    }
}