Electronic exchange apparatus synchronized with digital network

Abstract From the Canadian patent

A private branch exchange includes an oscillator for generating a reference clock defining the transmission frequency of a digital network, a clock generating circuit for generating a clock, whose frequency is slightly higher than that of the reference clock in, synchronization with the clock extracted from the digital network, and a selector which monitors whether or not the clock generating circuit is in a state in which it can operate properly, selects the output of the clock generating circuit when it is normal or the output of the oscillator when it is abnormal, and applies the selected output as a drive clock to a time-division switch for performing time-division multiplex …