| 摘要 |
A time slot is provided for each terminal unit or cable drop of a signal distribution system in a repeated sequence to communicate detected conditions "upstream". The time slots are defined in accordance with a time base responsive to broadcast time signals. An identification of each terminal unit is transmitted from a directional coupler corresponding to the terminal unit or cable drop after latching an output of a condition detector responsive to detection of a condition by a sequence of tones or tone pairs, preferably using circuits ubiquitous in the telecommunications industry. A printer is provided for each channel at a central facility and the transmitting terminal unit is identified in response to another time base operating synchronously with the time base defining the time slots and assigning the time slots to respective terminal units. Provision is made for synchronization of counters, error checking and control of polling frequency.
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