Rainbow-electronics ATtiny28L Bedienungsanleitung PDF herunterladen (Seite 22)

ATtiny28L/V

1062E–10/01

Power-down Mode When the SM bit is set (one), the SLEEP instruction forces the MCU into the Power-

down mode. In this mode, the external oscillator is stopped, while the external interrupts

and the Watchdog (if enabled) continue operating. Only an external reset, a Watchdog

reset (if enabled), or an external level interrupt can wake up the MCU.

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. This makes the MCU

less sensitive to noise. The wake-up period is equal to the clock-counting part of the

reset period (see Table 5). The MCU will wake up from power-down if the input has the

required level for two Watchdog oscillator cycles. If the wake-up period is shorter than

two Watchdog oscillator cycles, the MCU will wake up if the input has the required level

for the duration of the wake-up period. If the wake-up condition disappears before the

wake-up period has expired, the MCU will wake up from power-down without executing

the corresponding interrupt. The period of the Watchdog oscillator is 2.7 µs (nominal) at

3.0V and 25

°C. The frequency of the watchdog oscillator is voltage-dependent as

shown in the section “Typical Characteristics” on page 55.

When waking up from the Power-down mode, there is a delay from the wake-up condi-

tion until the wake-up becomes effective. This allows the clock to restart and become

stable after having been stopped.

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