atmega323l ATMEL Corporation, atmega323l Datasheet - Page 28

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

Power-on Reset
28
ATmega323(L)
Table 6 shows the start-up times from Reset. When the CPU wakes up from Power-
down or Power-save, only the clock counting part of the start-up time is used. The
Watchdog Oscillator is used for timing the Real Time part of the start-up time. The num-
ber WDT Oscillator cycles used for each time-out is shown in Table 7.
The frequency of the Watchdog Oscillator is voltage dependent as shown in the Electri-
cal Characteristics section. The device is shipped with CKSEL = “0010” (Internal RC
Oscillator, slowly rising power).
Table 7. Number of Watchdog Oscillator Cycles
Note:
A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. The detec-
tion level is defined in Table 5. The POR is activated whenever V
detection level. The POR circuit can be used to trigger the Start-up Reset, as well as to
detect a failure in supply voltage.
A Power-on Reset (POR) circuit ensures that the device is reset from Power-on. Reach-
ing the Power-on Reset threshold voltage invokes a delay counter, which determines
the delay, for which the device is kept in RESET after V
the delay counter can be defined by the user through the CKSEL Fuses. The different
selections for the delay period are presented in Table 6. The RESET signal is activated
again, without any delay, when the V
Figure 25. MCU Start-up, RESET Tied to V
INTERNAL
BODLEVEL
Unprogrammed
Unprogrammed
Unprogrammed
Unprogrammed
Programmed
Programmed
Programmed
Programmed
TIME-OUT
RESET
RESET
VCC
1. The BODLEVEL Fuse can be used to select start-up times even if the Brown-out
Detection is disabled (BODEN Fuse unprogrammed).
(1)
V
V
POT
RST
V
CC
t
TOUT
Condition
2.7V
2.7V
2.7V
2.7V
4.0V
4.0V
4.0V
4.0V
CC
decreases below detection level.
CC
Time-out
130 µs
4.2 ms
5.8 ms
67 ms
92 ms
30 µs
10 µs
35 µs
CC
rise. The time-out period of
Number of Cycles
CC
16K
64K
32
1K
32
4K
8
8
1457G–AVR–09/03
is below the