ATmega16 datasheet(27/315 Pages) ATMEL

27 / 315 page

ATmega16(L)

2466E–AVR–10/02

When this Oscillator is selected, start-up times are determined by the SUT fuses as

shown in Table 8.

Note:

1. This option should not be used when operating close to the maximum frequency of

the device.

Calibrated Internal RC

Oscillator

The Calibrated Internal RC Oscillator provides a fixed 1.0, 2.0, 4.0, or 8.0 MHz clock. All

frequencies are nominal values at 5V and 25

°C. This clock may be selected as the sys-

tem clock by programming the CKSEL fuses as shown in Table 9. If selected, it will

operate with no external components. The CKOPT Fuse should always be unpro-

grammed when using this clock option. During Reset, hardware loads the calibration

byte into the OSCCAL Register and thereby automatically calibrates the RC Oscillator.

At 5V, 25

°C and 1.0 MHz Oscillator frequency selected, this calibration gives a fre-

quency within ± 1% of the nominal frequency. 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, see the

section “Calibration Byte” on page 256.

Note:

1. The device is shipped with this option selected.

Table 7. External RC Oscillator Operating Modes

CKSEL3..0

Frequency Range (MHz)

0101

≤ 0.9

0110

0.9 - 3.0

0111

3.0 - 8.0

1000

8.0 - 12.0

Table 8. Start-up Times for the External RC Oscillator Clock Selection

SUT1..0

Start-up Time from

Power-down and

Power-save

Additional Delay

from Reset

CC = 5.0V)

Recommended Usage

18 CK

–

BOD enabled

18 CK

4.1 ms

Fast rising power

18 CK

65 ms

Slowly rising power

6 CK

(1)

4.1 ms

Fast rising power or BOD enabled

Table 9. Internal Calibrated RC Oscillator Operating Modes

CKSEL3..0

Nominal Frequency (MHz)

0001

(1)

1.0

0010

2.0

0011

4.0

0100

8.0

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