Datasheet

ATmega48PA/88PA/168PA [DATASHEET]

9223F–AVR–04/14

11.6 Watchdog System Reset

When the watchdog times out, it will generate a short reset pulse of one CK cycle duration. On the falling edge of this pulse,

the delay timer starts counting the time-out period t

TOUT

. Refer to Section 11.8 “Watchdog Timer” on page 45 for details on

operation of the watchdog timer.

Figure 11-6. Watchdog System Reset During Operation

11.7 Internal Voltage Reference

The Atmel

ATmega48PA/88PA/168PA features an internal bandgap reference. This reference is used for brown-out

detection, and it can be used as an input to the analog comparator or the ADC.

11.7.1 Voltage Reference Enable Signals and Start-up Time

The voltage reference has a start-up time that may influence the way it should be used. The start-up time is given in

Section 29.5 “System and Reset Characteristics” on page 272. To save power, the reference is not always turned on. The

reference is on during the following situations:

1. When the BOD is enabled (by programming the BODLEVEL [2:0] fuses).

2. When the bandgap reference is connected to the analog comparator (by setting the ACBG bit in ACSR).

3. When the ADC is enabled.

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.

1 CK Cycle

RESET

INTERNAL

RESET

Time-OUT

WDT

TIME-OUT

TOUT