Datasheet

CKSEL0 SUT1..0 Start-up time from
power-down and
power-save
Additional delay
from reset (VCC =
5.0V)
Recommended
usage
1 10 16K CK 14CK + 4.1ms Ceramic resonator,
fast rising power
1 11 16K CK 14CK + 65ms Ceramic resonator,
slowly rising power
1. Note: 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. Note: 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
frequency of the device, and if frequency stability at start-up is not important for the application.
Related Links
PSC clock sources on page 197
9.5. Calibrated Internal RC Oscillator
By default, the Internal RC Oscillator provides an 8.0MHz clock. Though voltage and temperature
dependent, this clock can be very accurately calibrated by the user. The device is shipped with the
CKDIV8 Fuse programmed.
This clock may be selected as the system clock by programming the CKSEL Fuses as shown in the
following Table. If selected, it will operate with no external components. During reset, hardware loads the
pre-programmed calibration value into the OSCCAL Register and thereby automatically calibrates the RC
Oscillator.
By changing the OSCCAL register from SW, it is possible to get a higher calibration accuracy than by
using the factory calibration.
When this Oscillator is used as the chip clock, the Watchdog Oscillator will still be used for the Watchdog
Timer and for the Reset Time-Out. For more information on the pre-programmed calibration value.
Table 9-5. Internal Calibrated RC Oscillator Operating Modes
Frequency Range
(1)
[MHz] CKSEL[3:0]
7.3 - 8.1 0010
(2)
Note:
1. If 8MHz frequency exceeds the specification of the device (depends on V
CC
), the CKDIV8 Fuse can
be programmed in order to divide the internal frequency by 8.
2. The device is shipped with this option selected.
When this Oscillator is selected, start-up times are determined by the SUT Fuses:
Atmel ATmega16M1/32M1/64M1 [DATASHEET]
Atmel-8209F-ATmega16M1/32M1/64M1_Datasheet_Complete-10/2016
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