| 摘要 |
PURPOSE:To promote miniaturizing and economical effects of a digital exchange by providing a means that generates a different DC voltage when a called telephone made a reply in plural subscribers' circuits and making ring trip operation for plural subscriber's circuits in common by discriminating the DC voltage. CONSTITUTION:A constant voltage diode 20 is provided in a call signal supply route as a device to generate a different DC voltage when a called telephone made a reply, and comparators 171, 172 and a gate 26 are provided in a ring trip circuit provided in common in subscribers' circuits 01, 02 as a means for discriminating DC voltage generated in each subscriber's circuit. The comparator 171 outputs a reset signal when a telephone set 11 changed from on-hook state to off-hook state, and the comparator 172 outputs a reset signal when either of telephone sets 11, 12 changed from on-hook state to off-hook state. By the ring trip circuit provided in common, it becomes possible to send out or stop a call signal when either of telephone sets 11 or 12 changed from on-hook state to off-hook state.
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