
52
7674F–AVR–09/09
ATmega164P/324P/644P
Figure 9-2.
External Reset During Operation
9.0.5
Brown-out Detection
ATmega164P/324P/644P has an On-chip Brown-out Detection (BOD) circuit for monitoring the
V
CC level during operation by comparing it to a fixed trigger level. The trigger level for the BOD
can be selected by the BODLEVEL Fuses. The trigger level has a hysteresis to ensure spike
free Brown-out Detection. The hysteresis on the detection level should be interpreted as V
BOT+ =
V
BOT + VHYST/2 and VBOT- = VBOT - VHYST/2.
When the BOD is enabled, and V
CC decreases to a value below the trigger level (VBOT- in Figure CC increases above the
trigger level (V
Time-out period t
TOUT has expired.
The BOD circuit will only detect a drop in V
CC if the voltage stays below the trigger level for lon-
ger than t
Figure 9-3.
Brown-out Reset During Operation
9.0.6
Watchdog 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 60 for details on operation of the Watchdog Timer.
CC
VCC
RESET
TIME-OUT
INTERNAL
RESET
VBOT-
VBOT+
tTOUT