Datasheet
33
ATtiny828 [DATASHEET]
8371A–AVR–08/12
6.6.3 OSCTCAL0A – Oscillator Temperature Calibration Register A
z Bits 7:0 – Oscillator Temperature Calibration Value
The temperature calibration value can be used to trim the calibrated 8MHz oscillator and remove temperature variations
from the oscillator frequency.
6.6.4 OSCTCAL0B – Oscillator Temperature Calibration Register B
z Bits 7:0 – Oscillator Temperature Calibration Value
The temperature calibration value can be used to trim the calibrated 8MHz oscillator and remove temperature variations
from the oscillator frequency.
6.6.5 OSCCAL1 – Oscillator Calibration Register
z Bits 7:0 – CAL[11:10]: Oscillator Calibration Value
The oscillator calibration register is used to trim the internal 32kHz oscillator and 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 Table 105 on page 250.
The application software can write this register to change the oscillator frequency. The oscillator can be calibrated to
frequencies as specified in Table 105 on page 250. Calibration outside that range is not guaranteed.
The lowest oscillator frequency is reached by programming these bits to zero. Increasing the register value increases the
oscillator frequency. A typical frequency response curve is shown in “ULP Oscillator Frequency vs. OSCCAL1 Value” on
page 296.
To ensure stable operation of the MCU the calibration value should be changed in small steps. A step change in
frequency of more than 2% from one cycle to the next can lead to unpredictable behavior. Also, the difference between
two consecutive register values should not exceed 0x20. If these limits are exceeded the MCU must be kept in reset
during changes to clock frequency.
Bit 76543210
(0xF0) Oscillator Temperature Calibration Data OSCTCAL0A
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value Device Specific Calibration Value
Bit 76543210
(0xF1) Oscillator Temperature Calibration Data OSCTCAL0B
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value Device Specific Calibration Value
Bit 76543210
(0x67) – – – – – – CAL11 CAL10 OSCCAL1
Read/Write RRRRRRR/WR/W
Initial Value 0 0 0 0 0 0 Calibration Value