ATtiny44 datasheet(27/236 Pages) ATMEL

27 / 236 page

8006H–AVR–10/09

ATtiny24/44/84

ibrates the RC Oscillator. The accuracy of this calibration is shown as Factory calibration in

Table 20-2 on page 176.

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

page 30, 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 20-2 on page 176.

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 162.

Note:

1. The device is shipped with this option selected.

When this oscillator is selected, start-up times are determined by the SUT Fuses as shown in

Table 6-5..

Note:

1. The device is shipped with this option selected.

2. If the RSTDISBL fuse is programmed, this start-up time will be increased to 14CK + 4 ms to

ensure programming mode can be entered.

6.2.3

Internal 128 kHz Oscillator

The 128 kHz internal oscillator is a low power oscillator providing a clock of 128 kHz. The fre-

quency depends on supply voltage, temperature and batch variations. This clock may be

selected as the system clock by programming the CKSEL Fuses to “0100”.

When this clock source is selected, start-up times are determined by the SUT Fuses as shown in

Table 6-6.

Note:

1. If the RSTDISBL fuse is programmed, this start-up time will be increased to 14CK + 4 ms to

ensure programming mode can be entered.

Table 6-4.

Internal Calibrated RC Oscillator Operating Modes

CKSEL3..0

Nominal Frequency

0010

(1)

8.0 MHz

Table 6-5.

Start-up Times for the Internal Calibrated RC Oscillator Clock Selection

SUT1..0

Start-up Time

from Power-down

Additional Delay from

Reset (VCC = 5.0V)

Recommended Usage

6 CK

14CK(2)

BOD enabled

6 CK

14CK + 4 ms

Fast rising power

10(1)

6 CK

14CK + 64 ms

Slowly rising power

Reserved

Table 6-6.

Start-up Times for the 128 kHz Internal Oscillator

SUT1..0

Start-up Time

from Power-down

Additional Delay

from Reset

Recommended

Usage

6 CK

14CK(1)

BOD enabled

6 CK

14CK + 4 ms

Fast rising power

6 CK

14CK + 64 ms

Slowly rising power

Reserved

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