Datasheet

9.11.1. Oscillator Calibration Register

Name: OSCCAL

Offset: 0x66

Reset: Device Specific Calibration Value

Property:

Bit 7 6 5 4 3 2 1 0

CAL7 CAL6 CAL5 CAL4 CAL3 CAL2 CAL1 CAL0

Access

R/W R/W R/W R/W R/W R/W R/W R/W

Reset x x x x x x x x

Bits 7:0 – CALn: Oscillator Calibration Value [n = 7:0]

The Oscillator Calibration Register is used to trim the Calibrated Internal RC Oscillator to remove process

variations from the oscillator frequency. A pre-programmed calibration value is automatically written to

this register during chip reset, giving the Factory calibrated frequency as specified in the Clock

Characteristics section of Electrical Characteristics chapter.. The application software can write this

the Clock Characteristics section of Electrical Characteristics chapter.. Calibration outside that range is

not guaranteed.

Note that this oscillator is used to time EEPROM and Flash write accesses, and these write times will be

affected accordingly. If the EEPROM or Flash are written, do not calibrate to more than 8.8MHz.

Otherwise, the EEPROM or Flash write may fail.

The CAL7 bit determines the range of operation for the oscillator. Setting this bit to 0 gives the lowest

frequency range, setting this bit to 1 gives the highest frequency range. The two frequency ranges are

overlapping, in other words a setting of OSCCAL=0x7F gives a higher frequency than OSCCAL=0x80.

The CAL[6:0] bits are used to tune the frequency within the selected range. A setting of 0x00 gives the

lowest frequency in that range, and a setting of 0x7F gives the highest frequency in the range.

Atmel ATmega16M1/32M1/64M1 [DATASHEET]

Atmel-8209F-ATmega16M1/32M1/64M1_Datasheet_Complete-10/2016