ATMEga64L ATMEL Corporation, ATMEga64L Datasheet - Page 52

• Manufacturer Part Number: ATMEga64L
• Description: 8-bit AVR Microcontroller with 64K Bytes In-System Programmable Flash
• Manufacturer: ATMEL Corporation

External Reset
Brown-out Detection
52
ATmega64(L)
An External Reset is generated by a low level on the RESET pin. Reset pulses longer
than the minimum pulse width (see Table 19) 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 25. External Reset during Operation
ATmega64 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 26. Borwn-out Reset During Operation
BOT+
BOT-
INTERNAL
TIME-OUT
RESET
RESET
= V
in Figure 26), the Brown-out Reset is immediately activated. When V
CC
V
BOT
CC
+ V
BOD
HYST
TOUT
given in Table 19.
/2 and V
has expired.
BOT+
BOT-
in Figure 26), the delay counter starts the MCU after the
V
BOT-
= V
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+
2490G–AVR–03/04
CC
increases
CC