Datasheet

12.10.1. OSCCAL – The Oscillator Calibration Register
When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used. When
addressing I/O Registers as data space using LD and ST instructions, 0x20 must be added to these offset
addresses.
Name: OSCCAL
Offset: 0x31
Reset: 0x00
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]
Writing the calibration byte to this address will trim the Internal Oscillator to remove process variations
from the Oscillator frequency. During Reset, the 1MHz 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 8.0MHz. Tuning
to other values is not guaranteed, as indicated in the following table.
Table 12-11. Internal RC Oscillator Frequency Range
OSCCAL Value Min Frequency in Percentage of
Nominal Frequency (%)
Max Frequency in Percentage of
Nominal Frequency (%)
0x00 50 100
0x7F 75 150
0xFF 100 200
Atmel ATmega32A [DATASHEET]
Atmel-8155I-ATmega32A_Datasheet_Complete-08/2016
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