Datasheet

41
ATtiny25/45/85 [DATASHEET]
2586Q–AVR–08/2013
Figure 8-4. External Reset During Operation
8.2.3 Brown-out Detection
ATtiny25/45/85 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 8-5), the Brown-
out Reset is immediately activated. When V
CC
increases above the trigger level (V
BOT+
in Figure 8-5), 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 longer than t
BOD
given
in “System and Reset Characteristics” on page 165.
Figure 8-5. Brown-out Reset During Operation
8.2.4 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 “Watchdog Timer” on page 42 for
details on operation of the Watchdog Timer.
CC
V
CC
RESET
TIME-OUT
INTERNAL
RESET
V
BOT-
V
BOT+
t
TOUT