Rainbow Electronics ATmega32L - Manual (Page 27)

27
ATmega32(L)
2503C–AVR–10/02
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 8.0 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 fre-
quency within ± 1% of the nominal frequency. 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 “Calibration Byte” on page 256.
Note: 1. The device is shipped with this option selected.
Table 7. External RC Oscillator Operating Modes
CKSEL3..0 Frequency Range (MHz)
0101 ≤ 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