11.3.2.2 Wake-Up Time

The normal wake-up time for the device is six main clock cycles (CLK_PER), plus the time it takes to start up the main clock source:
  • In Idle Sleep mode, the main clock source is kept running so it will not be any extra wake-up time.
  • In Standby Sleep mode, the main clock might be running so it depends on the peripheral configuration.
  • In Power-Down Sleep mode, only the ULP 32 KHz oscillator and RTC clock may be running if it is used by the BOD or WDT. All other clock sources will be OFF.
Table 11-3. Sleep Modes and Start-Up Time
Sleep Mode Start-Up Time
IDLE 6 CLK
Standby 6 CLK + OSC start-up
Power-Down 6 CLK + OSC start-up
The start-up time for the different clock sources is described in the Clock Controller (CLKCTRL) section.

In addition to the normal wake-up time, it is possible to make the device wait until the BOD is ready before executing code. This is done by writing 0x3 to the BOD Operation mode in Active and Idle bits (ACTIVE) in the BOD Configuration fuse (FUSE.BODCFG). If the BOD is ready before the normal wake-up time, the total wake-up time will be the same. If the BOD takes longer than the normal wake-up time, the wake-up time will be extended until the BOD is ready. This ensures correct supply voltage whenever code is executed.