Datasheet

44
ATmega16U4/32U4 [DATASHEET]
Atmel-7766J-USB-ATmega16U4/32U4-Datasheet_04/2016
Note that if a level triggered interrupt is used for wake-up from Power-down mode, the changed level must be
held for some time to wake up the MCU. Refer to “External Interrupts” on page 88 for details.
When waking up from Power-down mode, there is a delay from the wake-up condition occurs until the wake-up
becomes effective. This allows the clock to restart and become stable after having been stopped. The wake-up
period is defined by the same CKSEL Fuses that define the Reset Time-out period, as described in “Clock
Sources” on page 28.
7.4 Power-save Mode
When the SM2..0 bits are written to 011, the SLEEP instruction makes the MCU enter Power-save mode. For
compatibility reasons with AT90USB64/128 this mode is still present but since Timer 2 Asynchronous operation
is not present here, this mode is identical to Power-down.
7.5 Standby Mode
When the SM2..0 bits are 110 and an external crystal/resonator clock option is selected, the SLEEP instruction
makes the MCU enter Standby mode. This mode is identical to Power-down with the exception that the
Oscillator is kept running. From Standby mode, the device wakes up in six clock cycles.
7.6 Extended Standby Mode
When the SM2..0 bits are 111 and an external crystal/resonator clock option is selected, the SLEEP instruction
makes the MCU enter Extended Standby mode. For compatibility reasons with AT90USB64/128 this mode is
still present but since Timer 2 Asynchronous operation is not present here, this mode is identical to Standby-
mode.
Notes: 1. Only recommended with external crystal or resonator selected as clock source.
2. For INT6, only level interrupt.
3. Asynchronous USB interrupts are VBUSTI and WAKEUPI.
Table 7-1. Active Clock Domains and Wake-up Sources in the Different Sleep Modes
Active Clock
Domains
Oscillators Wake-up Sources
Sleep Mode
clk
CPU
clk
FLASH
clk
IO
clk
ADC
Main Clock Source Enabled INT6, INT3:0 and Pin Change TWI Address Match SPM/ EEPROM Ready ADC WDT Interrupt Other I/O USB Synchronous Interrupts USB Asynchronous Interrupts
(3)
Idle X X X X X X X X X X X
ADCNRM X X X
(2)
X X X X X X
Power-down X
(2)
X X X
Power-save X
(2)
X X X
Standby
(1)
X X
(2)
X X X
Extended
Standby
X X
(2)
X X X