ATtiny25 datasheet(25/196 Pages) ATMEL

25 / 196 page

7598H–AVR–07/09

ATtiny25/45/85

Notes:

1. These options should only be used when not operating close to the maximum frequency of the

device, and only if frequency stability at start-up is not important for the application. These

options are not suitable for crystals.

2. These options are intended for use with ceramic resonators and will ensure frequency stability

at start-up. They can also be used with crystals when not operating close to the maximum fre-

quency of the device, and if frequency stability at start-up is not important for the application.

6.5

Low-frequency Crystal Oscillator

To use a 32.768 kHz watch crystal as the clock source for the device, the low-frequency crystal

oscillator must be selected by setting CKSEL fuses to ‘0110’. The crystal should be connected

as shown in Figure 6-3. Refer to the 32 kHz Crystal Oscillator Application Note for details on

oscillator operation and how to choose appropriate values for C1 and C2.

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

Table 6-5.

Notes:

1. These options should only be used if frequency stability at start-up is not important for the

application.

Table 6-4.

Start-up Times for the Crystal Oscillator Clock Selection

CKSEL0

SUT1..0

Start-up Time from

Power-down and

Power-save

Additional Delay

from Reset

CC = 5.0V)

Recommended Usage

258 CK(1)

14CK + 4 ms

Ceramic resonator, fast

rising power

258 CK(1)

14CK + 64 ms

Ceramic resonator, slowly

rising power

010

1K CK(2)

14CK

Ceramic resonator, BOD

enabled

011

1K CK(2)

14CK + 4 ms

Ceramic resonator, fast

rising power

100

1K CK(2)

14CK + 64 ms

Ceramic resonator, slowly

rising power

16K CK

14CK

Crystal Oscillator, BOD

enabled

16K CK

14CK + 4 ms

Crystal Oscillator, fast

rising power

16K CK

14CK + 64 ms

Crystal Oscillator, slowly

rising power

Table 6-5.

Start-up Times for the Low Frequency Crystal Oscillator Clock Selection

SUT1..0

Start-up Time from

Power Down and Power

Save

Additional Delay from

Power On Reset

CC = 5.0V)

Recommended usage

1K CK(1)

4 ms

Fast rising power or BOD

enabled

1K CK(1)

64 ms

Slowly rising power

32K CK

64 ms

Stable frequency at start-up

Reserved

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