ATmega48/88/168
Table 9. Start-up Times for the Full Swing Crystal Oscillator Clock Selection
Start-up Time from
Power-down and
Power-save
Additional Delay
Oscillator Source /
Power Conditions
from Reset
(VCC = 5.0V)
CKSEL0 SUT1..0
Ceramic resonator, fast
rising power
258 CK
258 CK
1K CK
14CK + 4.1 ms(1)
14CK + 65 ms(1)
14CK(2)
0
0
0
0
1
00
01
10
11
00
01
10
11
Ceramic resonator,
slowly rising power
Ceramic resonator,
BOD enabled
Ceramic resonator, fast
rising power
1K CK
14CK + 4.1 ms(2)
14CK + 65 ms(2)
14CK
Ceramic resonator,
slowly rising power
1K CK
Crystal Oscillator, BOD
enabled
16K CK
16K CK
16K CK
1
1
1
Crystal Oscillator, fast
rising power
14CK + 4.1 ms
14CK + 65 ms
Crystal Oscillator,
slowly rising power
Notes: 1. These options should only be used when not operating close to the maximum fre-
quency of the device, and only if frequency stability at start-up is not important for the
application. These options are not suitable for crystals.
2. These options are intended for use with ceramic resonators and will ensure fre-
quency stability at start-up. They can also be used with crystals when not operating
close to the maximum frequency of the device, and if frequency stability at start-up is
not important for the application.
Low Frequency Crystal
Oscillator
The device can utilize a 32.768 kHz watch crystal as clock source by a dedicated Low
Frequency Crystal Oscillator. The crystal should be connected as shown in Figure 13.
When this Oscillator is selected, start-up times are determined by the SUT Fuses and
CKSEL0 as shown in Table 10.
Table 10. Start-up Times for the Low Frequency Crystal Oscillator Clock Selection
Start-up Time from
Power-down and
Power-save
Additional Delay
from Reset
Power Conditions
BOD enabled
(VCC = 5.0V)
CKSEL0 SUT1..0
1K CK
1K CK
14CK(1)
0
0
0
0
1
1
1
1
00
01
10
11
00
01
10
11
Fast rising power
Slowly rising power
14CK + 4.1 ms(1)
14CK + 65 ms(1)
1K CK
Reserved
32K CK
32K CK
32K CK
Reserved
BOD enabled
14CK
Fast rising power
Slowly rising power
14CK + 4.1 ms
14CK + 65 ms
Note:
1. These options should only be used if frequency stability at start-up is not important
for the application.
29
2545D–AVR–07/04
ATMEL [ ATMEL ]
