| 摘要 |
1,243,070. Telegraphy. C.I.T. COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS. 14 Oct., 1968 [15 Nov., 1967], No. 48649/68. Heading H4P. An arrangement in a telegraph exchange for initiating call-charging includes means for distinguishing between the "international call connected" signal and the "clearing" signal and subsequently for detecting a signal from the subscriber (the first character in the "answer back" sequence) indicating whether the call is chargeable. The embodiment described comprises a receiver R for polar 5-bit characters. Each character received on L is passed to store M1- M5. A bi-stable circuit B1 is enabled during an interval 130-140 m.sec. after the start of the received Start bit, i.e. an interval starting after the end of a character and ending before the end of a "call connected signal" (of 150 m.sec. duration). The bi-stable changes state if, when enabled, the signal on L is negative and all bits in the store are negative. This change of state indicates the presence of a "call connected" or "clearing" signal. A second bi-stable circuit B2 is enabled during an interval 180-200 m.sec., and changes state if B1 has changed state and, in this interval, the signal on L is positive, indicating that a "call connected" signal has been received. Transistor T1 gives an output initiating charging if B2 has changed state and the duration of three characters has elapsed and the last character stored has all of its bits positive, this character being the first of the "answer back" sequence and indicating that the call is chargeable. |
