| 摘要 |
PURPOSE:To facilitate an easy continuity test of the called subscriber circuit, by forming a digital loop in the called subscriber circuit by means of the ringing tone control signal. CONSTITUTION:The pad switch memory PSM can read and send the test pattern via the switch PSW and by the command of the central control unit CC after storing the form signal of the test pattern at its own part. The test pattern signal is sent to the called subscriber circuit LC through the time switch TSW and then returned at the digital loop circuit to reach the calling subscriber via the multiplex MPX and the switch TSW. Thus the time slot is sampled at the dropper D to be sent to the check circuit. Accordingly, no test pattern signal generating circuit is required in that case. Thus a continuity test is given simultaneously with transmission of the ringing tone, thus simplifying the timing process. |
