| 摘要 |
PURPOSE:To obtain necessary make and break outputs without being influenced by the length of a subscriber's line, by varying the digital threshold level for detecting whether a DC loop of a subscriber's line exists or not, by means of the relation which has been decided in advance, only when a dial pulse has been received. CONSTITUTION:When a subscriber 1 has made an off-hook, voltage Ei is generated from the output resistor 13 of the transistor (TR) 11, and this voltage is input to the analog multiplexer (AMUL) 18 through the TR16. The analog input which has been made time division multiple by the AMUL18 is varied to a digital amount by the A/D converter 19, and it is input to the microprocessor (muPC) 20. The muPC20 compares the digital threshold level A for detecting a call, which has been set in advance with the digital input value X, detects the call by X>A, and after that, stores the input value X, and calculates a new detection threshold level A' based on said input value. Accordingly, the threshold level A' is varied by a current flowing in the subscriber's line 2, and the make output and the break output which do not depend on this current value can be obtained. After the dial pulse has been received, the service in a stationary state is supervised by returning the threshold level A' to the threshold level A. |
