ATMEGA3290P datasheet(33/360 Pages) ATMEL

33 / 360 page

8021A–AVR–12/06

ATmega329P/3290P

automatically calibrates the RC Oscillator. The accuracy of this calibration is shown as Factory

calibration in Table 26-1 on page 331.

By changing the OSCCAL register from SW, see ”OSCCAL – Oscillator Calibration Register” on

page 35, 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 26-1 on page 331.

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 298.

Notes:

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 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 7-10 on page 33.

Note:

1. The device is shipped with this option selected

7.7

External Clock

To drive the device from an external clock source, XTAL1 should be driven as shown in Figure

7-4 on page 33. To run the device on an external clock, the CKSEL Fuses must be programmed

to “0000”.

Figure 7-4.

External Clock Drive Configuration

Table 7-9.

Internal Calibrated RC Oscillator Operating Modes

(1)(3)

Frequency Range(2) (MHz)

CKSEL3..0

7.3 - 8.1

0010

Table 7-10.

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 (VCC = 5.0V)

SUT1..0

BOD enabled

6 CK

14CK

Fast rising power

6 CK

14CK + 4.1 ms

Slowly rising power

6 CK

14CK + 65 ms(1)

Reserved

EXTERNAL

CLOCK

SIGNAL

XTAL2

XTAL1

GND

ATMEGA3290P Datasheet(PDF) 33 Page - ATMEL Corporation

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