Datasheet

48
2545T–AVR–05/11
ATmega48/88/168
Figure 11-5. Brown-out reset during operation.
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
page 49 for details on operation of the watchdog timer.
Figure 11-6. Watchdog system reset during operation.
11.7 Internal voltage reference
The Atmel ATmega48/88/168 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 “System and reset characteristics” on page 307. To save power, the ref-
erence 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.
V
CC
RESET
TIME-OUT
INTERNAL
RESET
V
BOT-
V
BOT+
t
TOUT
CK
CC