| 摘要 |
A telephone terminal device, which is activated by a predetermined number of ringing signals even if a telephone call occurred immediately after a previous caller had abandoned a call before engagement of the telephone line. When the telephone terminal device is set to standby mode, the polarity of telephone line (L1, L2) is stored in microprocessor CPU-1 via photocoupler PC-3 (or PC-4) and contact y2-1. If there is a call thereafter, ringing portion of the ringing signal is detected by photocoupler PC-3 (or PC-4) via capacitor C2. During a silent period, the polarity of the telephone line (L1, L2) is checked by the aforementioned PC-3 or PC-4 via contact y2-1 which is closed. When the polarity of the telephone line at the time of abandonment of call by a caller prior to activation of the telephone terminal device coincides with the aforementioned polarity stored, the telephone terminal device is restored to standby mode (with the counter for ranging signals being cleared).
|
