
25
2543L–AVR–08/10
ATtiny2313
Notes: 1. These options should only be used when not operating close to the maximum frequency of the
device, and only if frequency stability at start-up is not important for the application. These
options are not suitable for crystals.
2. These options are intended for use with ceramic resonators and will ensure frequency stability
at start-up. They can also be used with crystals when not operating close to the maximum fre-
quency of the device, and if frequency stability at start-up is not important for the application.
Calibrated Internal
RC Oscillator
The calibrated internal RC Oscillator provides a fixed 8.0 MHz clock. The frequency is nominal
value at 3V and 25
°C. If 8 MHz frequency exceeds the specification of the device (depends on
VCC), the CKDIV8 Fuse must be programmed in order to divide the internal frequency by 8 dur-
ing start-up. The device is shipped with the CKDIV8 Fuse programmed. This clock may be
selected as the system clock by programming the CKSEL Fuses as shown in
Table 6. If
selected, it will operate with no external components. During reset, hardware loads the calibra-
tion byte into the OSCCAL Register and thereby automatically calibrates the RC Oscillator. At
3V and 25
°C, this calibration gives a frequency within ± 10% of the nominal frequency. Using
calibration methods as described in application notes available at www.atmel.com/avr it is possi-
ble to achieve ± 2% accuracy at any given VCC 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
Note:
1. The device is shipped with this option selected.
Table 5. Start-up Times for the Crystal Oscillator Clock Selection
CKSEL0
SUT1..0
Start-up Time from
Power-down and
Power-save
Additional Delay
from Reset
(VCC = 5.0V)
Recommended Usage
0
00
14CK + 4.1 ms
Ceramic resonator, fast
rising power
0
01
14CK + 65 ms
Ceramic resonator,
slowly rising power
010
14CK
Ceramic resonator,
BOD enabled
011
14CK + 4.1 ms
Ceramic resonator, fast
rising power
100
14CK + 65 ms
Ceramic resonator,
slowly rising power
1
01
16K CK
14CK
Crystal Oscillator, BOD
enabled
1
10
16K CK
14CK + 4.1 ms
Crystal Oscillator, fast
rising power
1
11
16K CK
14CK + 65 ms
Crystal Oscillator,
slowly rising power
Table 6. Internal Calibrated RC Oscillator Operating Modes
CKSEL3..0
Nominal Frequency
0010 - 0011
4.0 MHz
0100 - 0101