ATmega16 datasheet(30/357 Pages) ATMEL

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2466S–AVR–05/09

ATmega16(L)

Oscillator Calibration

• Bits 7..0 – CAL7..0: Oscillator Calibration Value

Writing the calibration byte to this address will trim the Internal Oscillator to remove process vari-

ations 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 regis-

ter will increase the frequency of the Internal Oscillator. Writing $FF 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 fre-

quency. 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.

Bit

765

4321

CAL7

CAL6

CAL5

CAL4

CAL3

CAL2

CAL1

CAL0

OSCCAL

Read/Write

R/W

Initial Value

Device Specific Calibration Value

Table 11. Internal RC Oscillator Frequency Range.

OSCCAL Value

Min Frequency in Percentage of

Nominal Frequency (%)

Max Frequency in Percentage of

Nominal Frequency (%)

$00

100

$7F

150

$FF

100

200

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