Rainbow Electronics ATtiny2313 - Manual (Page 26)

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ATtiny2313
2543A–AVR–08/03
When this Oscillator is selected, start-up times are determined by the SUT Fuses as
shown in Table 7.
Note: 1. The device is shipped with this option selected.
Oscillator Calibration Register
– OSCCAL
• 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 unpredicatble behavior. Changes in
OSCCAL should not exceed 0x20 for each calibration.
Table 7. Start-up times for the internal calibrated RC Oscillator clock selection
SUT1..0
Start-up Time from Power-
down and Power-save
Additional Delay from
Reset (V
CC
= 5.0V) Recommended Usage
00 6 CK 14CK BOD enabled
01 6 CK 14CK + 4.1 ms Fast rising power
10 (1) 6 CK 14CK + 65 ms Slowly rising power
11 Reserved
Bit 7 6 5 4 3 2 1 0
– CAL6 CAL5 CAL4 CAL3 CAL2 CAL1 CAL0 OSCCAL
Read/Write R R/W R/W R/W R/W R/W R/W R/W
Initial Value Device Specific Calibration Value
Table 8. Internal RC Oscillator Frequency Range.
OSCCAL
Value
Min Frequency in Percentage of
Nominal Frequency
Max Frequency in Percentage of
Nominal Frequency
0x00 50% 100%
0x3F 75% 150%
0x7F 100% 200%