ATTINY24 Datasheet, PDF (27/238 Pages) ATMEL Corporation – 8-bit AVR Microcontroller with 2/4/8K Bytes In-System Programmable Flash

ATtiny24/44/84
ibrates the RC Oscillator. The accuracy of this calibration is shown as Factory calibration in
Table 20-2 on page 176.
By changing the OSCCAL register from SW, see “OSCCAL – Oscillator Calibration Register” on
page 30, 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 176.
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 162.
Table 6-4.
Internal Calibrated RC Oscillator Operating Modes
CKSEL3:0
0010 ⁽¹⁾
Nominal Frequency
8.0 MHz
Note: 1. The device is shipped with this option selected.
6.2.3
When this oscillator is selected, start-up times are determined by the SUT Fuses as shown in
Table 6-5.
Table 6-5.
SUT1:0
00
01
10⁽¹⁾
11
Start-up Times for the Internal Calibrated RC Oscillator Clock Selection
Start-up Time
from Power-down
6 CK
Additional Delay from
Reset (V_CC = 5.0V)
14CK⁽²⁾
Recommended Usage
BOD enabled
6 CK
14CK + 4 ms
Fast rising power
6 CK
14CK + 64 ms
Slowly rising power
Reserved
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.
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.
Table 6-6.
SUT1:0
00
01
10
11
Start-up Times for the 128 kHz Internal Oscillator
Start-up Time
from Power-down
6 CK
Additional Delay
from Reset
14CK⁽¹⁾
6 CK
14CK + 4 ms
6 CK
14CK + 64 ms
Reserved
Recommended
Usage
BOD enabled
Fast rising power
Slowly rising power
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.
27
8006J–AVR–08/10