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