Datasheet

29
2503P–AVR–07/10
ATmega32(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 unprogrammed when using
this clock option. During Reset, hardware loads the calibration byte for the 1 MHz into the OSC-
CAL 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 fre-
quency. 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 258.
Note: 1. The device is shipped with this option selected.
Table 7. External RC Oscillator Operating Modes
CKSEL3..0 Frequency Range (MHz)
0101 0.1 - 0.9
0110 0.9 - 3.0
0111 3.0 - 8.0
1000 8.0 - 12.0
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