Datasheet
32
8021G–AVR–03/11
ATmega329P/3290P
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 299.
Notes: 1. The device is shipped with this option selected.
2. The frequency ranges are preliminary values.
3. 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.
When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in
Table 8-10 on page 32.
Note: 1. The device is shipped with this option selected.
8.7 External Clock
To drive the device from an external clock source, XTAL1 should be driven as shown in Figure
8-3 on page 32. To run the device on an external clock, the CKSEL Fuses must be programmed
to “0000”.
Figure 8-3. External Clock Drive Configuration
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table 8-12 on page 33.
Table 8-9. Internal Calibrated RC Oscillator Operating Modes
(1)(3)
Frequency Range
(2)
(MHz) CKSEL3...0
7.3 - 8.1 0010
Table 8-10. 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 8-11. Crystal Oscillator Clock Frequency
CKSEL3...0 Frequency Range
ATmega329P/3290P 0000 0 - 20MHz
NC
EXTERNAL
CLOCK
SIGNAL
XTAL2
XTAL1
GND