ATmega165 datasheet(26/336 Pages) ATMEL

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ATmega165/V

2573G–AVR–07/09

Notes:

1. These options should only be used when not operating close to the maximum fre-

quency 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 fre-

quency stability at start-up. They can also be used with crystals when not operating

close to the maximum frequency of the device, and if frequency stability at start-up is

not important for the application.

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 the CKSEL Fuses to “0110” or “0111”. The

crystal should be connected as shown in Figure 12. When this Oscillator is selected,

start-up times are determined by the SUT Fuses as shown in Table 6 and CKSEL1..0 as

shown in Table 7.

Table 5. 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

(VCC = 5.0V)

Recommended Usage

258 CK(1)

14CK + 4.1 ms

Ceramic resonator, fast

rising power

258 CK(1)

14CK + 65 ms

Ceramic resonator,

slowly rising power

010

1K CK(2)

14CK

Ceramic resonator,

BOD enabled

011

1K CK(2)

14CK + 4.1 ms

Ceramic resonator, fast

rising power

100

1K CK(2)

14CK + 65 ms

Ceramic resonator,

slowly rising power

16K CK

14CK

Crystal Oscillator, BOD

enabled

16K CK

14CK + 4.1 ms

Crystal Oscillator, fast

rising power

16K CK

14CK + 65 ms

Crystal Oscillator,

slowly rising power

Table 6. Start-up Times for the Low-frequency Crystal Oscillator Clock Selection

SUT1..0

Additional Delay from Reset (VCC = 5.0V)

Recommended Usage

14CK

Fast rising power or BOD enabled

14CK + 4.1 ms

Slowly rising power

14CK + 65 ms

Stable frequency at start-up

Reserved

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