XMega External Interrupt
External interrupts are a must have feature in any microcontroller. Interrupts solve a lot of problem that would have otherwise been dependent on polling methods. For instance when we press the volume up key of a TV tuner’s remote controller, the remote controller quickly responds by transmitting the volume up command to the TV set and in turn the TV’s volume increases. This fast response is due to external interrupt issued by the remote’s button to the microcontroller it is connected to. If, however, all the keys of the remote were regularly and frequently scanned and then responded up on a press, the process would have been both slow and energy consuming because its microcontroller would then have never went to sleep or low power states and continuously kept scanning. In other words, the micro would have always ran despite no mandatory necessity and during standby conditions. This would have quickly drained the batteries. Since interrupt is typically used in such cases the remote controller will respond to a button press fast, wake up from sleep/idle/low power mode, transmit command data and then go back to sleep/idle/low power state. Thus the overall energy consumption is reduced while achieving fastest possible reaction. This is how real world applications work applying external interrupts.
