ATMEGA649V-8MI【PDF 43/146 页】IC AVR MCU FLASH 64K 1.8V 64QFN

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2552K–AVR–04/11

ATmega329/3290/649/6490

Note:

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.

8.4

Low-frequency Crystal Oscillator

To use a 32.768kHz 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 8-2. When this Oscillator is selected, start-up times are deter-

mined by the SUT Fuses as shown in Table 8-5 and CKSEL1..0 as shown in Table 8-6.

Note:

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

application

8.5

Calibrated Internal RC Oscillator

The calibrated Internal RC Oscillator by default provides a 8.0MHz 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.

011

1K CK(2)

14CK + 4.1ms

Ceramic resonator,

fast rising power

100

1K CK(2)

14CK + 65ms

Ceramic resonator,

slowly rising power

16K CK

14CK

Crystal Oscillator,

BOD enabled

16K CK

14CK + 4.1ms

Crystal Oscillator, fast

rising power

16K CK

14CK + 65ms

Crystal Oscillator,

slowly rising power

Table 8-4.

Start-up Times for the Crystal Oscillator Clock Selection (Continued)

CKSEL0

SUT1..0

Start-up Time from

Power-down and

Power-save

Additional Delay

from Reset

CC = 5.0V)

Recommended

Usage

Table 8-5.

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

SUT1..0

Additional Delay from Reset (V

CC = 5.0V)

Recommended Usage

14CK

Fast rising power or BOD enabled

14CK + 4.1ms

Slowly rising power

14CK + 65ms

Stable frequency at start-up

Reserved

Table 8-6.

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

CKSEL3..0

Start-up Time from

Power-down and Power-save

Recommended Usage

0110(1)

1K CK

0111

32K CK

Stable frequency at start-up

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