| 摘要 |
<p>An electronic telephone apparatus comprising a trunk circuit, a sync signal generating circuit, an oscillator circuit, a selector, and a time-division switch. The trunk circuit is connected between a digital line and a highway, for transmitting signals therebetween and extracting sync clock pulses from the digital line. The sync signal generating circuit is connected to the trunk circuit, for generating a first reference clock signal of a predetermined frequency from the clock pulses extracted by the trunk circuit. The oscillator circuit generate a second reference clock signal similar to the first reference sync signal. The selector monitors the first reference clock signal, it selects the first reference clock signal when no abnormality is found in the first reference clock signal, and selects the second reference clock signal when abnormality is found in the first reference clock signal. The time-division switch is driven by the reference clock signal output from the selector means, for performing time-division multiplexing on the data being transmitted through the highway. The electronic telephone apparatus can continuously perform its function even if the sync clock signal extracted from the digital line is not input to it due to the malfunction of the trunk circuit.</p> |
