Datasheet
27
8183F–AVR–06/12
ATtiny24A/44A/84A
By changing the OSCCAL register from SW, see “OSCCAL – Oscillator Calibration Register” on
page 31, it is possible to get a higher calibration accuracy than by using the factory calibration.
The accuracy of this calibration is shown as User calibration in Table 20-2 on page 175.
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 161.
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 6-5.
Note: 1. The device is shipped with this option selected.
2. If the RSTDISBL fuse is programmed, this start-up time will be increased to 14CK + 4 ms to
ensure programming mode can be entered.
6.2.3 Internal 128 kHz Oscillator
The 128 kHz internal oscillator is a low power oscillator providing a clock of 128 kHz. The fre-
quency depends on supply voltage, temperature and batch variations. This clock may be
selected as the system clock by programming the CKSEL Fuses to “0100”.
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table 6-6.
Note: 1. If the RSTDISBL fuse is programmed, this start-up time will be increased to 14CK + 4 ms to
ensure programming mode can be entered.
Table 6-4. Internal Calibrated RC Oscillator Operating Modes
CKSEL[3:0] Nominal Frequency
0010
(1)
8.0 MHz
Table 6-5. Start-up Times for the Internal Calibrated RC Oscillator Clock Selection
SUT[1:0]
Start-up Time
from Power-down
Additional Delay from
Reset (V
CC
= 5.0V) Recommended Usage
00 6 CK 14CK
(2)
BOD enabled
01 6 CK 14CK + 4 ms Fast rising power
10
(1)
6 CK 14CK + 64 ms Slowly rising power
11 Reserved
Table 6-6. Start-up Times for the 128 kHz Internal Oscillator
SUT[1:0]
Start-up Time
from Power-down
Additional Delay
from Reset
Recommended
Usage
00 6 CK 14CK
(1)
BOD enabled
01 6 CK 14CK + 4 ms Fast rising power
10 6 CK 14CK + 64 ms Slowly rising power
11 Reserved