Table 5. Start-up Times for the Crystal Oscillator Clock Selection
Start-up Time from
Power-down and
Power-save
Additional Delay
from Reset
CKSEL0 SUT1..0
(VCC = 5.0V)
Recommended Usage
0
0
0
0
1
00
01
10
11
00
01
10
11
258 CK(1)
258 CK(1)
1K CK(2)
1K CK(2)
1K CK(2)
16K CK
16K CK
16K CK
14CK + 4.1 ms
14CK + 65 ms
14CK
Ceramic resonator, fast
rising power
Ceramic resonator,
slowly rising power
Ceramic resonator,
BOD enabled
14CK + 4.1 ms
14CK + 65 ms
14CK
Ceramic resonator, fast
rising power
Ceramic resonator,
slowly rising power
Crystal Oscillator, BOD
enabled
1
1
1
14CK + 4.1 ms
14CK + 65 ms
Crystal Oscillator, fast
rising power
Crystal Oscillator,
slowly rising power
Notes: 1. These options should only be used when not operating close to the maximum fre-
quency 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 fre-
quency stability at start-up. They can also be used with crystals when not operating
close to the maximum frequency 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 during 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 compo-
nents. During reset, hardware loads the calibration 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 possible 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 “Calibration Byte” on page 159.
Table 6. Internal Calibrated RC Oscillator Operating Modes
CKSEL3..0
0010 - 0011
0100 - 0101
Nominal Frequency
4.0 MHz(1)
8.0 MHz
Note:
1. The device is shipped with this option selected.
24
ATtiny2313/V
2543F–AVR–08/04
ATMEL [ ATMEL ]
