The frequency of the internal RC oscillator depends on the temperature and operating voltage. An example of this dependency is in the figure below, which shows the frequency of the 8MHz RC oscillator of the ATmega8. The frequency increases with increasing voltage, and decreases with increasing operating temperature. These characteristics will vary from device to device. For details on a specific device, refer to its datasheet.
Figure 1. Calibrated 8MHz RC Oscillator Frequency vs. VCC (ATmega8)
