ATMEGA88 datasheet(49/374 Pages) ATMEL

49 / 374 page

2545J–AVR–12/06

ATmega48/88/168

Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC, the user

must always allow the reference to start up before the output from the Analog Comparator or

ADC is used. To reduce power consumption in Power-down mode, the user can avoid the three

conditions above to ensure that the reference is turned off before entering Power-down mode.

9.8

Watchdog Timer

9.8.1

Features

• Clocked from separate On-chip Oscillator

• 3 Operating modes

–Interrupt

– System Reset

– Interrupt and System Reset

• Selectable Time-out period from 16ms to 8s

• Possible Hardware fuse Watchdog always on (WDTON) for fail-safe mode

Figure 9-7.

Watchdog Timer

ATmega48/88/168 has an Enhanced Watchdog Timer (WDT). The WDT is a timer counting

cycles of a separate on-chip 128 kHz oscillator. The WDT gives an interrupt or a system reset

when the counter reaches a given time-out value. In normal operation mode, it is required that

the system uses the WDR - Watchdog Timer Reset - instruction to restart the counter before the

time-out value is reached. If the system doesn't restart the counter, an interrupt or system reset

will be issued.

In Interrupt mode, the WDT gives an interrupt when the timer expires. This interrupt can be used

to wake the device from sleep-modes, and also as a general system timer. One example is to

limit the maximum time allowed for certain operations, giving an interrupt when the operation

has run longer than expected. In System Reset mode, the WDT gives a reset when the timer

expires. This is typically used to prevent system hang-up in case of runaway code. The third

mode, Interrupt and System Reset mode, combines the other two modes by first giving an inter-

rupt and then switch to System Reset mode. This mode will for instance allow a safe shutdown

by saving critical parameters before a system reset.

128kHz

OSCILLATOR

WDP0

WDP1

WDP2

WDP3

WATCHDOG

RESET

WDE

WDIF

WDIE

MCU RESET

INTERRUPT

ATMEGA88 Datasheet(PDF) 49 Page - ATMEL Corporation

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