ATMEGA329 データシートの表示（PDF） - Atmel Corporation

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ATMEGA329

8-bit Microcontroller with In-System Programmable Flash

Atmel Corporation 

ATmega329/3290/649/6490

Table 9-4. Start-up Times for the Crystal Oscillator Clock Selection (Continued)

CKSEL0 SUT1..0

0

11

Start-up Time from

Power-down and

Power-save

1K CK(2)

1

00

1K CK(2)

Additional Delay

from Reset

(VCC = 5.0V)

14CK + 4.1 ms

14CK + 65 ms

Recommended

Usage

Ceramic resonator,

fast rising power

Ceramic resonator,

slowly rising power

1

01

16K CK

14CK

Crystal Oscillator,

BOD enabled

1

10

16K CK

14CK + 4.1 ms

Crystal Oscillator, fast

rising power

1

Note:

11

16K CK

14CK + 65 ms

Crystal Oscillator,

slowly rising power

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.

9.4 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 9-2. When this Oscillator is selected, start-up times are deter-

mined by the SUT Fuses as shown in Table 9-5 and CKSEL1..0 as shown in Table 9-6.

Table 9-5. Start-up Times for the Low-frequency Crystal Oscillator Clock Selection

SUT1..0

00

Additional Delay from Reset (VCC = 5.0V) Recommended Usage

14CK

Fast rising power or BOD enabled

01

14CK + 4.1 ms

Slowly rising power

10

14CK + 65 ms

Stable frequency at start-up

11

Reserved

Table 9-6. Start-up Times for the Low-frequency Crystal Oscillator Clock Selection

CKSEL3..0

0110(1)

Start-up Time from

Power-down and Power-save

1K CK

Recommended Usage

0111

32K CK

Stable frequency at start-up

Note: 1. This option should only be used if frequency stability at start-up is not important for the

application

9.5 Calibrated Internal RC Oscillator

The calibrated Internal RC Oscillator by default provides a 8.0 MHz clock. The frequency is nom-

inal value at 3V and 25°C. The device is shipped with the CKDIV8 Fuse programmed. See

“System Clock Prescaler” on page 32 for more details.

29

2552J–AVR–08/07

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