12.3.3.2 Wake-Up Time

The ordinary wake-up time for the device is six main clock cycles (CLK_PER), plus the time it takes to start the main clock source and the regulator if it has been switched off:
  • In Idle sleep mode, the main clock source is kept running to eliminate additional wake-up time
  • In Standby sleep mode, the main clock might be running depending on the peripheral configuration
  • In Power-Down sleep mode, only the OSC32K oscillator and the Real-Time Clock (RTC) may be running if the clock is used by the Brown-out Detector (BOD), Watchdog Timer (WDT), or Periodic Interrupt Timer (PIT). All the other clock sources will be OFF.
Table 12-5. Sleep Modes and Start-Up Time
Sleep ModeStart-Up Time
IdleSix clock cycles
StandbySix clock cycles + oscillator start-up time + regulator start-up time
Power-DownSix clock cycles + oscillator start-up time + regulator start-up time

The start-up time for the different clock sources is listed in the CLKCTRL - Clock Controller section. The start-up time for the regulator is included in the start-up time for the different clock sources.

In addition to the ordinary wake-up time, it is possible to make the device wait until the BOD is ready before executing the code. This is controlled by the BOD Operation in the Active and Idle Mode (ACTIVE) bit field in the BOD Configuration (FUSE.BODCFG) fuse. If the BOD is ready before the ordinary wake-up time, the total wake-up time will be the same. If the BOD takes longer than the ordinary wake-up time, the wake-up time will be extended until the BOD is ready, ensuring correct supply voltage whenever code is executed.