| 摘要 |
PURPOSE:To attain the nonpolar state of a transmission line by adding a code bit for deciding the polarity to the head of a transmission signal from a master set to a digital telephone set and deciding the polarity of transmission from the code bit at the receiving side so as to make the logic of the digital signal at the transmission side coincident with the received signal. CONSTITUTION:The master equipment 3 adds a polarity bit S to the head of a voice or data signal to a digital telephone set and gives an output while applying Manchester coding to the data. The digital telephone set 1 monitors an outgoing signal, decides the polarity from the polarity bit of a first input signal and switches the logic of the Manchester code in the voice or data sent afterward. Moreover, a clock component included in the Manchester code is extracted and used as a master synchronizing signal by establishing the synchronization. An incoming signal 5 from the digital telephone set 1 to the master set 3 does not include the polarity bit different from the outgoing signal and only the voice or data is subjected to Manchester coding according to the logic decided from the outgoing signal and the result is transmitted.
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