Datasheet

29
2466T–AVR–07/10
ATmega16(L)
When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in
Table 8.
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-
bration value, see the section “Calibration Byte” on page 261.
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
(V
CC
= 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 6 CK
(1)
4.1 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
(V
CC
= 5.0V) Recommended Usage
00 6 CK – BOD enabled
01 6 CK 4.1 ms Fast rising power
10
(1)
6 CK 65 ms Slowly rising power
11 Reserved