ATtiny2313/V
When this Oscillator is selected, start-up times are determined by the SUT Fuses as
shown in Table 7.
Table 7. Start-up times for the internal calibrated RC Oscillator clock selection
Start-up Time from Power-
down and Power-save
Additional Delay from
Reset (VCC = 5.0V)
SUT1..0
00
Recommended Usage
BOD enabled
6 CK
6 CK
6 CK
14CK
01
14CK + 4.1 ms
14CK + 65 ms
Reserved
Fast rising power
Slowly rising power
10(1)
11
Note:
1. The device is shipped with this option selected.
Oscillator Calibration Register
– OSCCAL
Bit
7
–
6
5
4
3
2
1
0
CAL6
R/W
CAL5
R/W
CAL4
R/W
CAL3
R/W
CAL2
R/W
CAL1
R/W
CAL0
R/W
OSCCAL
Read/Write
Initial Value
R
Device Specific Calibration Value
• Bits 6..0 – CAL6..0: Oscillator Calibration Value
Writing the calibration byte to this address will trim the internal Oscillator to remove pro-
cess variations from the Oscillator frequency. This is done automatically during Chip
Reset. When OSCCAL is zero, the lowest available frequency is chosen. Writing non-
zero values to this register will increase the frequency of the internal Oscillator. Writing
0x7F to the register gives the highest available frequency. The calibrated Oscillator is
used to time EEPROM and Flash access. If EEPROM or Flash is written, do not cali-
brate to more than 10% above the nominal frequency. Otherwise, the EEPROM or Flash
write may fail. Note that the Oscillator is intended for calibration to 8.0/4.0 MHz. Tuning
to other values is not guaranteed, as indicated in Table 8.
Avoid changing the calibration value in large steps when calibrating the Calibrated Inter-
nal RC Oscillator to ensure stable operation of the MCU. A variation in frequency of
more than 2% from one cycle to the next can lead to unpredictable behavior. Changes in
OSCCAL should not exceed 0x20 for each calibration.
Table 8. Internal RC Oscillator Frequency Range.
Min Frequency in Percentage of
Nominal Frequency
Max Frequency in Percentage of
Nominal Frequency
OSCCAL Value
0x00
50%
75%
100%
150%
200%
0x3F
0x7F
100%
25
2543F–AVR–08/04
ATMEL [ ATMEL ]
