
29
2466T–AVR–07/10
ATmega16(L)
When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in
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 MHz, 2.0 MHz, 4.0 MHz, or 8.0 MHz
clock. All frequencies 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
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, 2.0 MHz, 4.0
MHz or 8.0 MHz Oscillator frequency selected, this calibration gives a frequency within ±3% of
the nominal frequency. Using calibration methods as described in application notes available at
www.atmel.com/avr it is possible to achieve ±1% accuracy at any given V
CC and Temperature.
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 cali-
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
(VCC = 5.0V)
Recommended Usage
00
18 CK
–
BOD enabled
01
18 CK
4.1 ms
Fast rising power
10
18 CK
65 ms
Slowly rising power
11
4.1 ms
Fast rising power or BOD enabled
Table 9. Internal Calibrated RC Oscillator Operating Modes
CKSEL3..0
Nominal Frequency (MHz)
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
(VCC = 5.0V)
Recommended Usage
00
6 CK
–
BOD enabled
01
6 CK
4.1 ms
Fast rising power
6 CK
65 ms
Slowly rising power
11
Reserved