Datasheet

ATmega164A/PA/324A/PA/644A/PA/1284/P
 2018 Microchip Technology Inc. Data Sheet Complete DS40002070A-page 61
11.1.4 Brown-out Detection
ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P 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
+ 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
61), the Brown-out Reset is immediately activated. When V
CC
increases above the trigger level (V
BOT+
in Figure
11-5 on page 61), 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 longer than t
BOD
given in ”” on page 333.
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 63
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