Abstract: An improved clocking system for micro controllers is provided. The micro controller has two mechanisms by which the clocking is provided. One clock is provided by an external clock signal which is generally crystal controlled. A second mechanism for providing the clock is also present. This second clock can be useful as the "primary" or first clock which is generally a crystal oscillator may take several milliseconds to stabilize following a restart from a stop mode. The second clock mechanism can for example be an internal ring oscillator or other type of clock which although not as accurate as a crystal clock does not require the several milliseconds to recover.