Rainbow-electronics ATmega64L Instrukcja Użytkownika Pobierz pdf (Strona 27)

ATmega16(L)

2466B–09/01

Note: 1. This option should not be used when operating close to the maximum frequency of

the device.

Calibrated Internal RC

Oscillator

The calibrated internal RC oscillator provides a fixed 1.0, 2.0, 4.0, or 8.0 MHz clock. All

frequencies are nominal values at 5V and 25

°C. This clock may be selected as the sys-

tem clock by programming the CKSEL fuses as shown in Table 9. If selected, it will

operate with no external components. The CKOPT fuse should always be unpro-

grammed when using this clock option. During reset, hardware loads the calibration byte

into the OSCCAL register and thereby automatically calibrates the RC oscillator. At 5V,

°C and 1.0 MHz oscillator frequency selected, this calibration gives a frequency within

± 1% of the nominal frequency. When this oscillator is used as the chip clock, the

Watchdog Oscillator will still be used for the Watchdog Timer and for the reset time-out.

For more information on the pre-programmed calibration value, see the section “Calibra-

tion Byte” on page 255.

Note: 1. The device is shipped with this option selected.

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

shown in Table 10. XTAL1 and XTAL2 should be left unconnected (NC).

Note: 1. The device is shipped with this option selected.

Table 8. Start-up Times for the External RC Oscillator Clock Selection

SUT1..0

Start-up Time from

Power-down and

Power-save

Additional Delay

from Reset

= 5.0V) Recommended Usage

00 18 CK – BOD enabled

01 18 CK 4 ms Fast rising power

10 18 CK 64 ms Slowly rising power

11 6 CK

(1)

4 ms Fast rising power or BOD enabled

Table 9. Internal Calibrated RC Oscillator Operating Modes

CKSEL3..0 Nominal Frequency (MHz)

0001

(1)

1.0

0010 2.0

0011 4.0

0100 8.0

Table 10. Start-up Times for the Internal Calibrated RC Oscillator Clock Selection

SUT1..0

Start-up Time from

Power-down and

Power-save

Additional Delay

from Reset

= 5.0V) Recommended Usage

00 6 CK – BOD enabled

01 6 CK 4 ms Fast rising power

(1)

6 CK 64 ms Slowly rising power

11 Reserved

1 2 ... 22 23 24 25 26 27 28 29 30 31 32 ... 297 298

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