Rainbow Electronics Atmega169L - Manual (Page 28)

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ATmega169V/L
2514A–AVR–08/02
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 MHz. Tuning to
other values is not guaranteed, as indicated in Table 10.
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 10. 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%