ATMEGA649-16AI datasheet(29/375 Pages) ATMEL

29 / 375 page

ATmega329/3290/649/6490

2552H–AVR–11/06

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 10 on page 29.

Note:

1. The device is shipped with this option selected

OSCCAL – Oscillator

Calibration Register

• Bits 7:0 – CAL7:0: Oscillator Calibration Value

The Oscillator Calibration Register is used to trim the Calibrated Internal RC Oscillator

to remove process variations from the oscillator frequency. A pre-programmed calibra-

tion value is automatically written to this register during chip reset, giving the Factory

calibrated frequency as specified in Table 143 on page 319. The application software

can write this register to change the oscillator frequency. The oscillator can be calibrated

to frequencies as specified in Table 143 on page 319. Calibration outside that range is

not guaranteed.

Note that this oscillator is used to time EEPROM and Flash write accesses, and these

write times will be affected accordingly. If the EEPROM or Flash are written, do not cali-

brate to more than 8.8 MHz. Otherwise, the EEPROM or Flash write may fail.

The CAL7 bit determines the range of operation for the oscillator. Setting this bit to 0

gives the lowest frequency range, setting this bit to 1 gives the highest frequency range.

The two frequency ranges are overlapping, in other words a setting of OSCCAL = 0x7F

gives a higher frequency than OSCCAL = 0x80.

The CAL6..0 bits are used to tune the frequency within the selected range. A setting of

0x00 gives the lowest frequency in that range, and a setting of 0x7F gives the highest

frequency in the range.

Table 9. Internal Calibrated RC Oscillator Operating Modes

(1)(3)

Frequency Range(2) (MHz)

CKSEL3..0

7.3 - 8.1

0010

Table 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

Bit

7654

321

(0x66)

CAL7

CAL6

CAL5

CAL4

CAL3

CAL2

CAL1

CAL0

OSCCAL

Read/Write

R/W

Initial Value

Device Specific Calibration Value

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