Datasheet

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2549O–AVR–05/12
ATmega640/1280/1281/2560/2561
10.2 Clock Systems and their Distribution ...............................................................40
10.3 Clock Sources .................................................................................................41
10.4 Low Power Crystal Oscillator ...........................................................................42
10.5 Full Swing Crystal Oscillator ............................................................................44
10.6 Low Frequency Crystal Oscillator ....................................................................45
10.7 Calibrated Internal RC Oscillator .....................................................................47
10.8 128 kHz Internal Oscillator ..............................................................................47
10.9 External Clock .................................................................................................48
10.10 Clock Output Buffer .........................................................................................49
10.11 Timer/Counter Oscillator ..................................................................................49
10.12 System Clock Prescaler ..................................................................................49
10.13 Register Description ........................................................................................50
11 Power Management and Sleep Modes ................................................. 52
11.1 Sleep Modes ....................................................................................................52
11.2 Idle Mode .........................................................................................................52
11.3 ADC Noise Reduction Mode ............................................................................53
11.4 Power-down Mode ...........................................................................................53
11.5 Power-save Mode ............................................................................................53
11.6 Standby Mode .................................................................................................54
11.7 Extended Standby Mode .................................................................................54
11.8 Power Reduction Register ...............................................................................54
11.9 Minimizing Power Consumption ......................................................................54
11.10 Register Description ........................................................................................56
12 System Control and Reset .................................................................... 59
12.1 Resetting the AVR ...........................................................................................59
12.2 Reset Sources .................................................................................................59
12.3 Internal Voltage Reference ..............................................................................62
12.4 Watchdog Timer ..............................................................................................63
12.5 Register Description ........................................................................................67
13 I/O-Ports .................................................................................................. 70
13.1 Introduction ......................................................................................................70
13.2 Ports as General Digital I/O .............................................................................71
13.3 Alternate Port Functions ..................................................................................75
13.4 Register Description for I/O-Ports ..................................................................100
14 Interrupts .............................................................................................. 105