| 摘要 |
This invention is focused on the the microcomputer in the main system is connected with each microprocessor in the terminals by four lines. Two lines are used to supply the power and the others to communicate the data. Hence, the system may be simple and no dials are used in each terminal. There is no DC feeding current in the channels of the system. This method provides good transmission without the relays because of the adoption of PCM time-sharing method. The microprocessors detect the states of the keyboards and the hook switches so that those states are transmitted to the microcomputer. The microcomputer makes the microprocessors ring the tone-ringers.
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