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. BOD Disable...............................................................................................................................69
14.4. Idle Mode....................................................................................................................................69
14.5. ADC Noise Reduction Mode...................................................................................................... 69
14.6. Power-Down Mode.....................................................................................................................70
14.7. Power-Save Mode......................................................................................................................70
14.8. Standby Mode............................................................................................................................ 71
14.9. Extended Standby Mode............................................................................................................71
14.10. Power Reduction Register......................................................................................................... 71
14.11. Minimizing Power Consumption................................................................................................. 71
14.12. Register Description...................................................................................................................73
15. System Control and Reset.......................................................................................78
15.1. Resetting the AVR...................................................................................................................... 78
15.2. Reset Sources............................................................................................................................78
15.3. Power-on Reset..........................................................................................................................79
15.4. External Reset............................................................................................................................80
15.5. Brown-out Detection...................................................................................................................80
15.6. Watchdog System Reset............................................................................................................81
15.7. Internal Voltage Reference.........................................................................................................81
15.8. Watchdog Timer......................................................................................................................... 82
15.9. Register Description................................................................................................................... 84
16. Interrupts................................................................................................................. 88
16.1. Interrupt Vectors in ATmega48PA.............................................................................................. 88
16.2. Interrupt Vectors in ATmega88PA.............................................................................................. 89
16.3. Interrupt Vectors in ATmega168PA............................................................................................ 92
16.4. Register Description................................................................................................................... 95
17. EXTINT - External Interrupts................................................................................... 98
17.1. Pin Change Interrupt Timing.......................................................................................................98
ATmega48PA/88PA/168PA
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Datasheet Complete
DS40002011A-page 4