ATmega48/88/168
Figure 10-5. Brown-out Reset During Operation
VBOT+
VCC
VBOT-
RESET
t
TOUT
TIME-OUT
INTERNAL
RESET
10.6 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 tTOUT. Refer to
page 50 for details on operation of the Watchdog Timer.
Figure 10-6. Watchdog System Reset During Operation
CC
CK
10.7 Internal Voltage Reference
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.
10.7.1
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 308. 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.
49
2545M–AVR–09/07
ATMEL [ ATMEL ]
