| 摘要 |
PURPOSE:To reduce remarkably components by replacing a privacy call function with a line busy display function. CONSTITUTION:When a call signal from an external line comes to an indoor line, the call signal is inputted to external line terminals 1, 2 of all switches A(A1-A3) and telephone sets B1-B3 are called at the same time. When a handset of an optional telephone set, e.g., a set B1, is hooked off, the talking between the external line and the telephone set B1 is started, busy display lamps 8 of the talking switches A1-A3 are lighted respectively to display that other telephone sets are busy. Thus, the privacy call state in the said telephone set is maintained.
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