ATMEGA329 データシートの表示（PDF） - Atmel Corporation
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ATMEGA329 Datasheet PDF : 392 Pages
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This clock may be selected as the system clock by programming the CKSEL Fuses as shown in
Table 9-7 on page 30. 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. The accuracy of this calibration is shown as Factory
calibration in Table 29-2 on page 329.
By changing the OSCCAL register from SW, see “OSCCAL – Oscillator Calibration Register” on
page 32, it is possible to get a higher calibration accuracy than by using the factory calibration.
The accuracy of this calibration is shown as User calibration in Table 29-2 on page 329.
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 cali-
bration value, see the section “Calibration Byte” on page 296.
Table 9-7.
Internal Calibrated RC Oscillator Operating Modes(1)(3)
Frequency Range(2) (MHz)
CKSEL3..0
7.3 - 8.1
0010
Note: 1. The device is shipped with this option selected.
2. The frequency ranges are preliminary values. Actual values are TBD.
3. If 8 MHz frequency exceeds the specification of the device (depends on VCC), the CKDIV8
Fuse can be programmed in order to divide the internal frequency by 8.
When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in
Table 9-8 on page 30.
Table 9-8. Start-up times for the internal calibrated RC Oscillator clock selection
Power Conditions
BOD enabled
Fast rising power
Slowly rising power
Start-up Time from Power-
down and Power-save
6 CK
6 CK
6 CK
Reserved
Additional Delay from
Reset (VCC = 5.0V)
14CK
14CK + 4.1 ms
14CK + 65 ms(1)
SUT1..0
00
01
10
11
Note: 1. The device is shipped with this option selected.
30 ATmega329/3290/649/6490
2552J–AVR–08/07
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