10.2
10.3
10.4
10.5
10.6
10.7
10.8
10.9
Clock Systems and their Distribution ...............................................................39
Clock Sources .................................................................................................40
Low Power Crystal Oscillator ...........................................................................41
Full Swing Crystal Oscillator ............................................................................43
Low Frequency Crystal Oscillator ....................................................................45
Calibrated Internal RC Oscillator .....................................................................46
128 kHz Internal Oscillator ..............................................................................47
External Clock .................................................................................................47
10.10 Clock Output Buffer .........................................................................................48
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
11.2
11.3
11.4
11.5
11.6
11.7
11.8
11.9
Sleep Modes ....................................................................................................52
Idle Mode .........................................................................................................52
ADC Noise Reduction Mode ............................................................................53
Power-down Mode ...........................................................................................53
Power-save Mode ............................................................................................53
Standby Mode .................................................................................................54
Extended Standby Mode .................................................................................54
Minimizing Power Consumption ......................................................................54
Register Description ........................................................................................56
12 System Control and Reset .................................................................... 59
12.1
12.2
12.3
12.4
12.5
Resetting the AVR ...........................................................................................59
Reset Sources .................................................................................................59
Internal Voltage Reference ..............................................................................62
Watchdog Timer ..............................................................................................63
Register Description ........................................................................................67
13 I/O-Ports .................................................................................................. 70
13.1
13.2
13.3
13.4
Introduction ......................................................................................................70
Ports as General Digital I/O .............................................................................71
Alternate Port Functions ..................................................................................75
Register Description for I/O-Ports ..................................................................100
14 Interrupts .............................................................................................. 105
14.1
Interrupt Vectors in ATmega640/1280/1281/2560/2561 ................................105
ii
ATmega640/1280/1281/2560/2561
2549L–AVR–08/07
ATMEL [ ATMEL ]
