atmega323l ATMEL Corporation, atmega323l Datasheet - Page 29

• Manufacturer Part Number: atmega323l
• Description: Atmega323 8-bit Avr Microcontroller With 32k Bytes Of In-system Programmable Flash
• Manufacturer: ATMEL Corporation

External Reset
Brown-out Detection
1457G–AVR–09/03
Figure 26. MCU Start-up, RESET Extended Externally
An External Reset is generated by a low level on the RESET pin. Reset pulses longer
than 500 ns 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
Period t
Figure 27. External Reset During Operation
ATmega323 has an On-chip Brown-out Detection (BOD) circuit for monitoring the V
level during the operation. The BOD circuit can be enabled/disabled by the fuse
BODEN. When the BOD is enabled (BODEN programmed), and V
value below the trigger level, the Brown-out Reset is immediately activated. When V
increases above the trigger level, the Brown-out Reset is deactivated after a delay. The
delay is defined by the user in the same way as the delay of POR signal, in Table 6. 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 of 50 mV to ensure spike free Brown-out Detection.
The BOD circuit will only detect a drop in V
for longer than 9 µs for trigger level 4.0V, 21 µs for trigger level 2.7V (typical values).
INTERNAL
TIME-OUT
RESET
RESET
VCC
TOUT
RST
has expired.
on its positive edge, the delay timer starts the MCU after the Time-out
V
POT
V
CC
RST
if the voltage stays below the trigger level
t
TOUT
ATmega323(L)
CC
decreases to a
29
CC
CC