
50
8018P–AVR–08/10
ATmega169P
10.2.3
Brown-out Detection
ATmega169P 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 VCC decreases to a
value below the trigger level (V
vated. When V
CC increases above the trigger level (VBOT+ in Figure 10-5), 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
Figure 10-5. Brown-out Reset During Operation
10.2.4
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
Figure 10-6. Watchdog Reset During Operation
VCC
RESET
TIME-OUT
INTERNAL
RESET
VBOT-
VBOT+
tTOUT
CK
CC