ATMEGA8L ATMEL [ATMEL Corporation], ATMEGA8L Datasheet - Page 38

• Manufacturer Part Number: ATMEGA8L
• Description: 8-bit AVR with 8K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

External Reset
Brown-out Detection
38
ATmega8(L)
An External Reset is generated by a low level on the RESET pin. Reset pulses longer
than the minimum pulse width (see Table 15) will generate a reset, even if the clock is
not running. Shorter pulses are not guaranteed to generate a reset. When the applied
signal reaches the Reset Threshold Voltage – V
counter starts the MCU after the time-out period t
Figure 17. External Reset During Operation
ATmega8 has an On-chip Brown-out Detection (BOD) circuit for monitoring the V
level during operation by comparing it to a fixed trigger level. The trigger level for the
BOD can be selected by the fuse BODLEVEL to be 2.7V (BODLEVEL unprogrammed),
or 4.0V (BODLEVEL programmed). The trigger level has a hysteresis to ensure spike
free Brown-out Detection. The hysteresis on the detection level should be interpreted as
V
The BOD circuit can be enabled/disabled by the fuse BODEN. When the BOD is
enabled (BODEN programmed), and V
(V
above the trigger level (V
time-out period t
The BOD circuit will only detect a drop in V
for longer than t
Figure 18. Brown-out Reset During Operation
BOT+
BOT-
= V
in Figure 18), the Brown-out Reset is immediately activated. When V
CC
BOT
INTERNAL
TIME-OUT
+ V
RESET
RESET
BOD
V
TOUT
HYST
CC
given in Table 15.
has expired.
/2 and V
BOT+
BOT-
in Figure 18), the delay counter starts the MCU after the
V
= V
BOT-
BOT
CC
- V
decreases to a value below the trigger level
CC
HYST
if the voltage stays below the trigger level
/2.
TOUT
RST
has expired.
on its positive edge, the delay
V
t
TOUT
BOT+
2486M–AVR–12/03
CC
increases
CC