Clock generator with selectable frequency and glich-free reset function

摘要

A selector 11 selects one of a plurality of reference clock signals based upon a selection signal. A hardware reset signal 103 is delayed by a predetermined time. The selection signal is sent to the selector responsive to a set signal. The sending of the selection signal is stopped responsive to the delayed hardware reset signal. The set signal is delayed by a predetermined time. A first flip-flop 13 is set in response to the hardware reset signal or a software reset signal, is supplied with the delayed set signal as a count input, and is supplied with low level as a data input. A second flip-flop 16 receives a logic AND signal of an output signal from the selector 11 and the hardware reset signal as a count input and receives a logic OR signal of the output of the first flip-flop 13 and an inverted output of the second flip-flop 16 as a count signal, and generates a clock output which is free of glitches when being stopped or started.