ATMEGA8-16AI SL383 Atmel, ATMEGA8-16AI SL383 Datasheet - Page 30

• Manufacturer Part Number: ATMEGA8-16AI SL383
• Description: Semiconductors and Actives, Microprocessors, Microcontrollers
• Manufacturer: Atmel

Calibrated Internal
RC Oscillator
30
ATmega8(L)
The calibrated internal RC Oscillator provides a fixed 1.0, 2.0, 4.0, or 8.0 MHz clock. All frequen-
cies are nominal values at 5V and 25°C. This clock may be selected as the system clock by
programming the CKSEL Fuses as shown in
components. The CKOPT Fuse should always be unprogrammed when using this clock option.
During reset, hardware loads the 1 MHz calibration byte into the OSCCAL Register and thereby
automatically calibrates the RC Oscillator. At 5V, 25°C and 1.0 MHz Oscillator frequency
selected, this calibration gives a frequency within ± 3% of the nominal frequency. Using run-time
calibration methods as described in application notes available at www.atmel.com/avr it is possi-
ble to achieve ± 1% accuracy at any given V
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
“Calibration Byte” on page
Table 9. Internal Calibrated RC Oscillator Operating Modes
Note:
When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in
Table
or Timer Oscillator pins..
Table 10. Start-up Times for the Internal Calibrated RC Oscillator Clock Selection
Note:
SUT1..0
10
00
01
11
10. PB6 (XTAL1/TOSC1) and PB7(XTAL2/TOSC2) can be used as either general I/O pins
(1)
1. The device is shipped with this option selected.
1. The device is shipped with this option selected.
CKSEL3..0
0001
0010
0011
0100
Start-up Time from
Power-down and
(1)
Power-save
6 CK
6 CK
6 CK
225.
Additional Delay
(V
from Reset
CC
Table
4.1 ms
Reserved
CC
65 ms
= 5.0V)
–
Nominal Frequency (MHz)
and Temperature. When this Oscillator is used
9. If selected, it will operate with no external
1.0
2.0
4.0
8.0
Recommended Usage
BOD enabled
Fast rising power
Slowly rising power
2486W–AVR–02/10