Abstract: An oscillation circuit stops the oscillation of an external oscillator to reduce the current consumed when a frequency lower than the inherent frequency of the external oscillator is supplied to a microcomputer. A PLL circuit 37 generates a second clock 45 from a first clock 23 output by an oscillation circuit 1. A PLL lock signal 47 is changed from a first level to a second level when the second clock 45 is generated. A selector 39 outputs the second clock 45 as an internal clock 13 when the PLL lock signal 47 is at the second level. The operation of an oscillator 9 is stopped when the PLL lock signal 47 is at the second level.

Abstract: A data output buffer circuit for a semiconductor integrated circuit has a plurality of output buffer circuits. Each output buffer circuit has an input terminal for receiving input data and an output buffer having first and second switching circuits serially connected between two high and low power source terminals. Each of the first and second switching circuits has a control terminal for turning on and off each of the first and second switching circuits upon receipt of a control signal at the control terminals. A timing signal input terminal receives a timing signal with which the output buffer circuit operates in synchronism. A timing switch connects the next stage of the input terminal and is turned on by the timing signal. A delay signal is connected between the timing switch means and the control terminals of the first and second switching circuits and delays the input data from the input terminal and transmits the delayed input data to the control terminals of the first and second switching circuits.