Datasheet

46
7766E–AVR–04/10
ATmega16U4/ATmega32U4
7.7.1 Power Reduction Register 0 - PRR0
• Bit 7 - PRTWI: Power Reduction TWI
Writing a logic one to this bit shuts down the TWI by stopping the clock to the module. When
waking up the TWI again, the TWI should be re initialized to ensure proper operation.
• Bit 6 - Res: Reserved bit
This bits is reserved and will always read as zero.
• Bit 5 - PRTIM0: Power Reduction Timer/Counter0
Writing a logic one to this bit shuts down the Timer/Counter0 module. When the Timer/Counter0
is enabled, operation will continue like before the shutdown.
• Bit 4 - Res: Reserved bit
This bit is reserved and will always read as zero.
• Bit 3 - PRTIM1: Power Reduction Timer/Counter1
Writing a logic one to this bit shuts down the Timer/Counter1 module. When the Timer/Counter1
is enabled, operation will continue like before the shutdown.
• Bit 2 - PRSPI: Power Reduction Serial Peripheral Interface
Writing a logic one to this bit shuts down the Serial Peripheral Interface by stopping the clock to
the module. When waking up the SPI again, the SPI should be re initialized to ensure proper
operation.
• Bit 1 - Res: Reserved bit
These bits are reserved and will always read as zero.
• Bit 0 - PRADC: Power Reduction ADC
Writing a logic one to this bit shuts down the ADC. The ADC must be disabled before shut down.
The analog comparator cannot use the ADC input MUX when the ADC is shut down.
7.7.2 Power Reduction Register 1 - PRR1
• Bit 7 - PRUSB: Power Reduction USB
Writing a logic one to this bit shuts down the USB by stopping the clock to the module. When
waking up the USB again, the USB should be re initialized to ensure proper operation.
• Bit 6..5 - Res: Reserved bits
These bits are reserved and will always read as zero.
Bit 7654321 0
PRTWI PRTIM2 PRTIM0 – PRTIM1 PRSPI - PRADC PRR0
Read/Write R/W R/W R/W R R/W R/W R R/W
Initial Value0000000 0
Bit 7 654 3 210
PRUSB – – PRTIM4 PRTIM3 – – PRUSART1 PRR1
Read/Write R/W R R R R/W R R R/W
Initial Value 0 0 0 0 0 0 0 0