Datasheet

ii
2545T–AVR–05/11
ATmega48/88/168
9.5Low frequency crystal oscillator ..............................................................................33
9.6Calibrated internal RC oscillator ..............................................................................33
9.7128kHz internal oscillator ........................................................................................34
9.8External clock ..........................................................................................................35
9.9Clock output buffer ..................................................................................................35
9.10Timer/counter oscillator .........................................................................................36
9.11System clock prescaler .........................................................................................36
9.12Register description ...............................................................................................37
10 Power management and sleep modes ................................................. 39
10.1Sleep modes .........................................................................................................39
10.2Idle mode ...............................................................................................................39
10.3ADC noise reduction mode ...................................................................................40
10.4Power-down mode ................................................................................................40
10.5Power-save mode .................................................................................................40
10.6Standby mode .......................................................................................................41
10.7Power reduction register .......................................................................................41
10.8Minimizing power consumption .............................................................................41
10.9Register description ...............................................................................................43
11 System control and reset ...................................................................... 45
11.1Resetting the AVR .................................................................................................45
11.2Reset sources .......................................................................................................45
11.3Power-on reset ......................................................................................................46
11.4External reset ........................................................................................................47
11.5Brown-out detection ..............................................................................................47
11.6Watchdog system reset .........................................................................................48
11.7Internal voltage reference ......................................................................................48
11.8Watchdog timer .....................................................................................................49
11.9Register description ...............................................................................................53
12 Interrupts ................................................................................................ 56
12.1Overview ...............................................................................................................56
12.2Interrupt vectors in ATmega48 ..............................................................................56
12.3Interrupt vectors in Atmel ATmega88 ....................................................................58
12.4Interrupt vectors in Atmel ATmega168 ..................................................................61
12.5Register description ...............................................................................................64
13 External interrupts ................................................................................. 66