ATMEGA164P_1 Datasheet, PDF (52/377 Pages) ATMEL Corporation – 8-bit Microcontroller with 16/32/64K Bytes In-System Programmable Flash

Figure 9-2. External Reset During Operation
CC
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 + 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
9-3 on page 52), the Brown-out Reset is immediately activated. When V_CC increases above the
trigger level (V_BOT+ in Figure 9-3 on page 52), 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 “System and Reset Characteristics” on page 332.
Figure 9-3. Brown-out Reset During Operation
V_CC
V_BOT-
V_BOT+
RESET
TIME-OUT
t_TOUT
9.0.6
Watchdog Reset
INTERNAL
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.
52 ATmega164P/324P/644P
7674F–AVR–09/09