AVR External Interrupts Revision as of 17:52, 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.

Basics

Steps to configure the Interrupts:

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

General Interrupt Control Register (GICR)

The GICR Register shown below is used to enable INT0 and INT1 interrupts. These interrupts correspond to the two physical pins PD3 and PD4 respectively. The INT0 is configured to produce low level triggered and INT1 as falling edge triggered interrupt respectively. A counter is increment and displayed when the interrupt occurs.

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

MCU Control Register (MCUCR) The MCUCR register allows us to configure the type of interrupt we need as shown by the table below:

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.