Datasheet

13. System Clock and Clock Options............................................................................ 53
13.1. Clock Systems and Their Distribution........................................................................................ 53
13.2. Clock Sources............................................................................................................................ 54
13.3. Low-Power Crystal Oscillator..................................................................................................... 56
13.4. Full Swing Crystal Oscillator.......................................................................................................58
13.5. Low-Frequency Crystal Oscillator.............................................................................................. 59
13.6. Calibrated Internal RC Oscillator................................................................................................60
13.7. 128 kHz Internal Oscillator......................................................................................................... 61
13.8. External Clock............................................................................................................................ 62
13.9. Timer/Counter Oscillator.............................................................................................................63
13.10. Clock Output Buffer....................................................................................................................63
13.11. System Clock Prescaler............................................................................................................. 63
13.12. Register Description...................................................................................................................64
14. Power Management and Sleep Modes................................................................... 68
14.1. Overview.................................................................................................................................... 68
14.2. Sleep Modes.............................................................................................................................. 68
14.3. Idle Mode....................................................................................................................................69
14.4. ADC Noise Reduction Mode...................................................................................................... 69
14.5. Power-Down Mode.....................................................................................................................69
14.6. Power-Save Mode......................................................................................................................70
14.7. Standby Mode............................................................................................................................ 70
14.8. Extended Standby Mode............................................................................................................70
14.9. Power Reduction Register..........................................................................................................71
14.10. Minimizing Power Consumption.................................................................................................71
14.11. Register Description................................................................................................................... 72
15. System Control and Reset.......................................................................................77
15.1. Resetting the AVR...................................................................................................................... 77
15.2. Reset Sources............................................................................................................................77
15.3. Power-on Reset..........................................................................................................................78
15.4. External Reset............................................................................................................................79
15.5. Brown-out Detection...................................................................................................................79
15.6. Watchdog System Reset............................................................................................................80
15.7. Internal Voltage Reference.........................................................................................................80
15.8. Watchdog Timer......................................................................................................................... 81
15.9. Register Description................................................................................................................... 83
16. Interrupts................................................................................................................. 87
16.1. Interrupt Vectors in ATmega48A................................................................................................ 87
16.2. Interrupt Vectors in ATmega88A................................................................................................ 88
16.3. Interrupt Vectors in ATmega168A.............................................................................................. 91
16.4. Register Description................................................................................................................... 94
17. EXTINT - External Interrupts................................................................................... 97
17.1. Pin Change Interrupt Timing.......................................................................................................97
17.2. Register Description................................................................................................................... 98
ATmega48A/88A/168A
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Datasheet Complete
DS40002007A-page 4