SN8F2270B Series
USB 2.0 Low-Speed 8-Bit Micro-Controller
5.3 WAKEUP
5.3.1 OVERVIEW
Under power down mode (sleep mode) or green mode, program doesn’t execute. The wakeup trigger can wake the
system up to normal mode or slow mode. The wakeup trigger sources are external trigger (P0, P1 level change),
internal trigger (T0 timer overflow) and USB bus toggle.
z
z
Power down mode is waked up to normal mode. The wakeup trigger is only external trigger (P0, P1 level change
and USB bus toggle)
Green mode is waked up to last mode (normal mode or slow mode). The wakeup triggers are external trigger (P0,
P1 level change), internal trigger (T0 timer overflow) and USB bus toggle.
5.3.2 WAKEUP TIME
When the system is in power down mode (sleep mode), the high clock oscillator stops. When waked up from power
down mode, MCU waits for 4 internal 6MHz clock or 2048 external 6MHz clocks as the wakeup time to stable the
oscillator circuit. After the wakeup time, the system goes into the normal mode.
Note: Wakeup from green mode is no wakeup time because the clock doesn’t stop in green mode.
The value of the wakeup time is as the following.
“6MHz IHRC” mode:
The Wakeup time = 1/Fosc * 2048 (sec) + high clock start-up time
Note: The high clock start-up time is depended on the VDD and oscillator type of high clock.
Example: In 6MHz IHRC mode and power down mode (sleep mode), the system is waked up. After the wakeup
time, the system goes into normal mode. The wakeup time is as the following.
The wakeup time = 1/Fosc * 2048 = 0.341 ms (Fosc = 6MHz)
The total wakeup time = 0.1705 ms + internal high RC oscillator start-up time
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