Datasheet

31
7766F–AVR–11/10
ATmega16/32U4
Notes: 1. These options should only be used when not operating close to the maximum frequency 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 frequency stability
at start-up. They can also be used with crystals when not operating close to the maximum fre-
quency of the device, and if frequency stability at start-up is not important for the application.
Note: 1.
The device is shipped with this option selected.
6.4 Low Frequency Crystal Oscillator
The device can utilize a 32.768 kHz watch crystal as clock source by a dedicated Low Fre-
quency Crystal Oscillator. The crystal should be connected as shown in Figure 6-2. When this
Oscillator is selected, start-up times are determined by the SUT Fuses and CKSEL0 as shown in
Table 6-6.
Ceramic resonator,
slowly rising power
1K CK 14CK + 65 ms
(2)
100
Crystal Oscillator, BOD
enabled
16K CK 14CK 1 01
Crystal Oscillator, fast
rising power
16K CK 14CK + 4.1 ms 1 10
Crystal Oscillator,
slowly rising power
16K CK 14CK + 65 ms 1 11
Table 6-5. Start-up times for the internal calibrated RC Oscillator clock selection
Power Conditions
Start-up Time from Power-
down and Power-save
Additional Delay from
Reset (V
CC
= 5.0V) SUT1..0
BOD enabled 6 CK 14CK 00
Fast rising power 6 CK 14CK + 4.1 ms 01
Slowly rising power 6 CK 14CK + 65 ms
(1)
10
Reserved 11
Table 6-4. Start-up Times for the Low Power Crystal Oscillator Clock Selection (Continued)
Oscillator Source /
Power Conditions
Start-up Time from
Power-down and
Power-save
Additional Delay
from Reset
(V
CC
= 5.0V) CKSEL0 SUT1..0
Table 6-6. Start-up Times for the Low Frequency Crystal Oscillator Clock Selection
Power Conditions
Start-up Time from
Power-down and
Power-save
Additional Delay
from Reset
(V
CC
= 5.0V) CKSEL0 SUT1..0
BOD enabled 1K CK 14CK
(1)
000
Fast rising power 1K CK 14CK + 4.1 ms
(1)
001
Slowly rising power 1K CK 14CK + 65 ms
(1)
010
Reserved 0 11
BOD enabled 32K CK 14CK 1 00
Fast rising power 32K CK 14CK + 4.1 ms 1 01
Slowly rising power 32K CK 14CK + 65 ms 1 10
Reserved 1 11