Datasheet

29
2503Q–AVR–02/11
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, 2.0, 4.0, or 8.0MHz 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 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 1MHz into the OSCCAL Register and
thereby automatically calibrates the RC Oscillator. At 5V, 25°C and 1.0MHz Oscillator frequency
selected, this calibration gives a frequency within ±3% of the nominal frequency. Using calibra-
tion 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 calibration value, see the section “Cali-
bration 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 4.1ms Fast rising power
10 18 CK 65ms Slowly rising power
11 6 CK
(1)
4.1ms 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