AVR External Interrupts Revision as of 17:20, 19 March 2016 by Sandeep (Talk | contribs) (diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)

We have looked at the basics of AVR Interrupts, now let us go ahead and use the External Interrupts feature on the AVR MCUs.

Steps to configure the Interrupts:

1. Set Global Interrupt(I-bit) Enable bit in the AVR Status Register(SREG)
2. Set INT1 and INT0 bits in the General Interrupt Control Register (GICR)
3. Configure MCU Control Register (MCUCR) to select interrupt type.
4. Handle the interrupt in the Interrupt Service Routine code.

The Registers

General Interrupt Control Register (GICR)

7	6	5	4	3	2	1	0
INT1	INT0	INT2	-	-	-	IVSEL	IVCE

MCU Control Register (MCUCR)

7	6	5	4	3	2	1	0
SE	SM2	SM1	SM0	ISC11	ISC10	ISC01	ISC00

ISC01	ISC00	Description
0	0	The low level of INT0 generates an interrupt request.
0	1	Any logical change on INT0 generates an interrupt request.
1	0	The falling edge of INT0 generates an interrupt request.
1	1	The rising edge of INT0 generates an interrupt request.

General Interrupt Flag Register(GIFR)

7	6	5	4	3	2	1	0
INTF1	INTF0	INTF2	-	-	-	-	-

We will connect two switches to the two interrupt pins and show the status on a LCD. The connections are shown in the image below.

The Code

#include<avr/io.h>
#include<avr/interrupt.h>
#include<util/delay.h>
#include "lcd.h"
 
volatile int cnt_zero,cnt_one;
 
ISR (INT0_vect)          //External interrupt_zero ISR
{
	cnt_zero++;
}
 
ISR (INT1_vect)        //External interrupt_one ISR
{
	cnt_one++;
 
}
 
int main()
{
	DDRC=0xff;   //Configure PORTC(Lcd databus) as output
	DDRD=0xe0;   //Configure INT0,INT1 as input and PORTD5-PORTD7(rs,rw,en) as output
 
	LCD_SetUp(PB_0,PB_1,PB_2,P_NC,P_NC,P_NC,P_NC,PB_4,PB_5,PB_6,PB_7);
	LCD_Init(2,16);
 
	GICR=0xc0;   //Enable External Interrupts INT0 and INT1
	MCUCR=0x08;  //Configure INT0 active low level triggered and INT1 as falling edge
 
	sei();     // Enable global interrupts by setting global interrupt enable bit in SREG
 
	while(1)
	{
		LCD_Printf("EINT0:%4u\n",cnt_zero);
		LCD_Printf("EINT1:%4u\n",cnt_one);
	}
}