ATMEGA8L ATMEL [ATMEL Corporation], ATMEGA8L Datasheet - Page 28

• Manufacturer Part Number: ATMEGA8L
• Description: 8-bit AVR with 8K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Calibrated Internal RC
Oscillator
28
ATmega8(L)
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,
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 possible to achieve ± 1% accu-
racy at any given V
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 sec-
tion “Calibration Byte” on page 221.
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 10. PB6 (XTAL1/TOSC1) and PB7(XTAL2/TOSC2) can be used as
either general I/O pins or Timer Oscillator pins..
Table 10. Start-up Times for the Internal Calibrated RC Oscillator Clock Selection
Note:
SUT1..0
10
00
01
11
(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
CC
6 CK
6 CK
6 CK
and Temperature. When this Oscillator is used as the chip clock,
Additional Delay
(V
from Reset
CC
4.1 ms
Reserved
65 ms
= 5.0V)
–
Nominal Frequency (MHz)
1.0
2.0
4.0
8.0
Recommended Usage
BOD enabled
Fast rising power
Slowly rising power
2486M–AVR–12/03