Datasheet

53
8272E–AVR–04/2013
ATmega164A/PA/324A/PA/644A/PA/1284/P
11.1.4 Brown-out Detection
ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P has an On-chip Brown-out Detec-
tion (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
+ V
HYST
/2 and V
BOT-
= V
BOT
- V
HYST
/2.
When the BOD is enabled, and V
CC
decreases to a value below the trigger level (V
BOT-
in Figure
11-5 on page 53), the Brown-out Reset is immediately activated. When V
CC
increases above the
trigger level (V
BOT+
in Figure 11-5 on page 53), the delay counter starts the MCU after the 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
BOD
given in ”” on page 337.
Figure 11-5. Brown-out Reset during operation.
11.1.5 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
”Watchdog Timer” on page 55 for details on operation of the Watchdog Timer.
Figure 11-6. Watchdog Reset during operation.
V
CC
RESET
TIME-OUT
INTERNAL
RESET
V
BOT-
V
BOT+
t
TOUT
CK
CC