SINGLE CHIP MICROCOMPUTER

摘要

PURPOSE:To quicken a rise time of oscillation, and to shorten an oscillation stable time by switching a power source of a low frequency oscillator to an output of a boosting circuit or an internal power source by an output of a counter, and applying a high voltage at the time of rise of an operation. CONSTITUTION:When a crystal oscillator is connected between oscillator connection terminals 11, 12, and the oscillator is connected to a high frequency oscillator side, as well, and electric power is supplied to a power source terminal 16 of this single chip microcomputer, first of all, the high frequency oscillator oscillates, an oscillating signal is outputted to an internal high frequency oscillator output terminal 18, and a boosting circuit 17 operates. Also, by constituting a switching circuit in advance so that an output of the boosting circuit 17 is selected, the output of the boosting circuit 17 is supplied to a power source of a low frequency oscillator 13. As for the oscillator 13, the output of the boosting circuit 17 of a higher voltage than that of the internal power source terminal 16 is supplied, therefore, its oscillation is stabilized in a short time. In such a state, when the count number of a counter 14 becomes a prescribed value, the power source of the low frequency oscillator 13 is switched to the internal power source terminal 16 by the switching circuit 15, and operated by low power.