ATMEGA8L ATMEL [ATMEL Corporation], ATMEGA8L Datasheet - Page 29

• Manufacturer Part Number: ATMEGA8L
• Description: 8-bit AVR with 8K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Oscillator Calibration Register
– OSCCAL
2486M–AVR–12/03
• Bits 7..0 – CAL7..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. During Reset, the 1 MHz calibration value
which is located in the signature row High byte (address 0x00) is automatically loaded
into the OSCCAL Register. If the internal RC is used at other frequencies, the calibration
values must be loaded manually. This can be done by first reading the signature row by
a programmer, and then store the calibration values in the Flash or EEPROM. Then the
value can be read by software and loaded into the OSCCAL Register. 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 0xFF 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 calibrate 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 1.0, 2.0, 4.0, or 8.0 MHz. Tuning to other values is
not guaranteed, as indicated in Table 11.
Table 11. Internal RC Oscillator Frequency Range
Bit
Read/Write
Initial Value
OSCCAL Value
0x00
0x7F
0xFF
CAL7
R/W
7
Min Frequency in Percentage of
CAL6
R/W
6
Nominal Frequency (%)
CAL5
R/W
5
Device Specific Calibration Value
100
50
75
CAL4
R/W
4
CAL3
R/W
3
Max Frequency in Percentage of
CAL2
R/W
2
Nominal Frequency (%)
CAL1
ATmega8(L)
R/W
1
100
150
200
CAL0
R/W
0
OSCCAL
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