ATmega328P datasheet(29/448 Pages) ATMEL

29 / 448 page

8161D–AVR–10/09

ATmega48PA/88PA/168PA/328P

Figure 8-2.

Crystal Oscillator Connections

The Low Power Oscillator can operate in three different modes, each optimized for a specific fre-

quency range. The operating mode is selected by the fuses CKSEL3..1 as shown in Table 8-3

on page 29.

Notes:

1. This is the recommanded CKSEL settings for the difference frenquency ranges.

2. This option should not be used with crystals, only with ceramic resonators.

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. It must be ensured

that the resulting divided clock meets the frequency specification of the device.

The CKSEL0 Fuse together with the SUT1..0 Fuses select the start-up times as shown in Table

8-4.

Table 8-3.

Low Power Crystal Oscillator Operating Modes

(3)

Frequency Range

(MHz)

Recommended Range for

Capacitors C1 and C2 (pF)

CKSEL3..1(1)

0.4 - 0.9

–

100(2)

0.9 - 3.0

12 - 22

101

3.0 - 8.0

12 - 22

110

8.0 - 16.0

12 - 22

111

Table 8-4.

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

Oscillator Source /

Power Conditions

Start-up Time from

Power-down and

Power-save

Additional Delay

from Reset

(VCC = 5.0V)

CKSEL0

SUT1..0

Ceramic resonator, fast

rising power

258 CK

14CK + 4.1 ms(1)

000

Ceramic resonator, slowly

rising power

258 CK

14CK + 65 ms(1)

001

Ceramic resonator, BOD

enabled

1K CK

14CK(2)

010

Ceramic resonator, fast

rising power

1K CK

14CK + 4.1 ms(2)

011

Ceramic resonator, slowly

rising power

1K CK

14CK + 65 ms(2)

100

XTAL2 (TOSC2)

XTAL1 (TOSC1)

GND

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