ATMega32 External Interrupt Example

External interrupt is an external notification to the micro-controller. Usually, an external event (sense) such as logic changing, or edge triggering.

In ATMega32, there are three external interrupt source, INT0, INT1 and INT2. Each source locate at different pins.

1. INT0 at PD2
2. INT1 at PD3
3. INT2 at PB2

For events could trigger the interrupt:

1. Low logic level
2. Logic changing
3. Falling edge
4. Rising Edge

To program the interrupt, set up the code in the following step:

1. Set the interrupt input pin as digital input
2. Enable the interrupt for the corresponding input
3. Enable the global interrupt control
4. Keep your main program loop working
5. Write the interrupt service routine to handle the corresponding interrupt

In ATMega32 the external interrupt is controlled by the GICR (General Interrupt Control Register).

General Interrupt Control Register

We enable any external interrupt by giving "1" to the source. For example, external interrupt 1 is enabled by setting INT1=1.

Interrupt flag contain the information about the state of any presenting interrupt. GIFR (General Interrupt Flage Register) store the status of external interrupts.

GIFR (General Interrupt Flag Register)

We can test any each external interrupt flag of this register to find the interrupt source. For example, we find INTF1=1, that mean that external interrupt INT1 is occur.

There are four modes of event (sense) the trigger the interrupt, as mention about. Those senses are controlled in the MCU Control Register (MCUCR).

MCUCR (MCU Control Register)

The ISC11 and ISC10, are the interrupt sense control of INT1.

The ISC01 and ISC00, are the interrupt sense control of INT0

There four mode of sense as refers to the datasheet. By default, they sense Low to trigger interrupt.

The Interrupt Service Routine (ISR) is a block of source code uses for handling the interrupt. They are short because the interrupt must not take to long to complete.

The ISR locates at the interrupt vector. Each interrupt source has their own interrupt vector. For example INT0_vect is an interrupt vector for external interrupt 0.

In this example, I use all three external interrupt sources. The interrupt sense is logic low. So when I make any external interrupt pin low, it will generate the interrupt. The ISR is to toggle LED output each corresponding to the source.

Schematic and Simulation Diagram.
We have external interrupt, INT0, INT1 and INT2
connect to its individual active low push button.
Each interrupt toggles the corresponding output LEDs. 

Source code:

#include <avr/io.h> 
#include "avr/interrupt.h" 
 
 int main(void) 
 { 
 //PA7.5 ARE OUTPUT 
 DDRA=(1<<5)|(1<<6)|(1<<7); 
 //PB2 USED FOR INT2 
 PORTB=(1<<2); 
 //INT0 AND INT1 
 PORTD=(1<<2)|(1<<3); 
 //SET EXTERNAL INTERRUPT FOR INT0, INT1 AND INT1 
 GICR=(1<<7)|(1<<6)|(1<<5); 
 //SET GLOBLE INTERRUPT 
 sei(); 
     while (1)  
     { 
     } 
 } 
 
 /* 
 Interrupt Service Routine for 
 Interrupt0 
 */ 
 ISR(INT0_vect){ 
 //Toggle PA5 
 PORTA^=(1<<5); 
 } 
 
 /* 
 Interrupt Service Routine for 
 Interrupt1 
 */ 
 ISR(INT1_vect){ 
 //Toggle PA6 
 PORTA^=(1<<6); 
 } 
 
 /* 
 Interrupt Service Routine for 
 Interrupt2 
 */ 
 ISR(INT2_vect){ 
 //Toggle PA7 
 PORTA^=(1<<7); 
 }

Back to main tutorial page ATMega32 tutorials in C with Atmel Studio 7.

Click here to download this example.

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