| 摘要 |
PURPOSE:To perform the level up and adjustment of a sound volume at the time of placing a handset call, by providing a sound volume level up key. CONSTITUTION:The ON and OFF states of a Mic key are decided by the state of an off-hook handset call, and when it is set at the ON state, the loudspeaking of a reception call that is the function of a key telephone set is performed. On the other hand, when it is set at the OFF state, the ON and OFF states of the sound volume level up key is decided, and when it is set at the OFF state, an ordinary handset call is performed, and when it is set at the ON state, a sound volume level change-over switch 13 is turned ON, and a sound volume level up call via a sound volume level up circuit 12 is performed. Also, at this time, it is possible to adjust the sound volume by a sound volume adjusting button 41.
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