| 摘要 |
PURPOSE:To build up function having only to connect the unit of each function by providing a talking changeover between an external telephone set and an extension, trunk line holding, its release as telephone exchange functions as units by each function. CONSTITUTION:In the telephone exchange 1, a trunk line 2 from a central office, a talking line 4 connecting to a doorphone 3, are connected as external lines and plural sets of internal lines 5 comprising extensions and control lines are connected. Plural slave sets 6 each provided with a telephone receptacle 7 are connected to each internal line 5. A trunk line interface unit provided with an incoming detection section and a holding circuit is provided in the inside of the exchange 1 and a trunk line changeover relay or the like provided to 4-wire slave set 6 connected to the internal line 5 is provided. Each unit is connected to each individual printed board in a form of a card and the required functions are added freely in response to the scale of the system by inserting the units to the connector provided to the mother board.
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