26
ATmega161(L)
1228B–09/01
Note:
1. The Power-on Reset will not work unless the supply voltage has been below V
POT
(falling).
‘
Notes:
1. The CKSEL fuses control only the start-up time. The oscillator is the same for all
selections. On Power-up, the real-time part of the start-up time is increased with typ.
0.6 ms.
2. Or external Power-on Reset.
3. When BOD is enabled, there will be a real-time part = 50 µs (typ)
4. Table 4 shows the start-up times from reset. From sleep, 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 number WDT oscillator cycles used for each time-out is
shown in Table 5.
Table 3.
Reset Characteristics (V
CC
= 5.0V)
Symbol
Parameter
Condition
Min
Typ
Max
Units
V
POT
Power-on Reset Threshold
Voltage (rising)
BOD disabled
1.0
1.4
1.8
V
BOD enabled
1.7
2.2
2.7
V
Power-on Reset Threshold
Voltage (falling)
BOD disabled
0.4
0.6
0.8
V
BOD enabled
1.7
2.2
2.7
V
V
RST
RESET Pin Threshold
Voltage
0.85 V
CC
V
V
BOT
Brown-out Reset Threshold
Voltage
(BODLEVEL = 1)
2.6
2.7
2.8
V
(BODLEVEL = 0)
3.8
4.0
4.2
Table 4.
Reset Delay Selections
CKSEL
[2:0]
Start-up Time, V
CC
= 2.7V,
BODLEVEL Unprogrammed
Start-up Time, V
CC
= 4.0V,
BODLEVEL Programmed
Recommended
Usage
000
4.2 ms + 6 CK
5.8 ms + 6 CK
External Clock, Fast
Rising Power
001
30 µs + 6 CK
10 µs + 6 CK
External Clock,
BOD Enabled
010
67 ms + 16K CK
92 ms + 16K CK
Crystal Oscillator,
Slowly Rising
Power
011
4.2 ms + 16K CK
5.8 ms + 16K CK
Crystal Oscillator,
Fast Rising Power
100
30 µs + 16K CK
10 µs + 16K CK
Crystal Oscillator,
BOD Enabled
101
67 ms + 1K CK
92 ms + 1K CK
Ceramic
Resonator/External
Clock, Slowly Rising
Power
110
4.2 ms + 1K CK
5.8 ms + 1K CK
Ceramic Resonator,
Fast Rising Power
111
30 µs + 1K CK
10 µs + 1K CK
Ceramic Resonator,
BOD Enabled