STUFF SYNCHRONIZATION CONTROL METHOD

PURPOSE:To realize an oscillator with low cost and the miniaturization of the accessory circuit by selecting the oscillating frequency of a clock by a standby oscillator used when an input signal is interrupted sufficiently lower than the frequency of the low-order input signal in a stuff synchronizing type multiple converter. CONSTITUTION:If the input signal is interrupted, a signal representing the input interruption being an output of an input interruption detection circuit 30 throws a clock changeover circuit 50' to the position of the standby oscillator 82. The oscillated frequency of the standby oscillator 82 is equal to the frequency of the stuff pulse insertion and sufficiently lower than the frequency of the low- dimension input signal. The output is fed to an inhibit circuit 60 via a leading edge detection circuit 85 to be triggered at a frequency corresponding to the frequency and the clock changeover circuit 50'. On the other hand, the output of a high-order group frequency oscillator 90' is fed to the inhibit circuit 60 via a read clock generating circuit 70, the stuff pulse is inserted at a part required for the insertion by using a signal from the standby oscillator 82 via a leading detection circuit 85 and the output is transferred to a multiplex section via a storage device 20.