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Apparatus for signalling system

  • US 4,308,430 A
  • Filed: 11/14/1979
  • Issued: 12/29/1981
  • Est. Priority Date: 11/14/1979
  • Status: Expired due to Term
First Claim
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1. In a signalling system, apparatus comprising:

  • first and second apparatus at first and second locations, respectively, and interconnected by a transmission medium for allowing communication between the first and second apparatus;

    said first apparatus at the first location comprising;

    first means arranged at or following a specified time of day to initiate a self-check call and to apply self-check message data to the transmission medium for transmission to the second apparatus at the second location;

    said second apparatus at the second location comprising;

    storage means arranged to store self-check timing data specifying a time of day at which the first means of the first apparatus at the first location is scheduled to initiate a self-check call and apply self-check message data to the transmission medium for transmission to the second apparatus;

    processing means arranged to receive self-check message data generated by the first means of the first apparatus and operative when self-check message data is received thereby to update the self-check timing data in the storage means to specify the time of day at which the next self-check call is to be initiated by the first means, said processing means being operative in the absence of self-check message data from the first means not to update the self-check timing data in the storage means; and

    present time means operative to produce time-of-day data representing the present time of day;

    said processing means being further operative on a regular basis to access the self-check timing data in the storage means and to compare the self-check timing data with the time-of-day data produced by the present time means and representing the present time of day, said processing means being operative if the self-check timing data in the storage means at the time of accessing the storage means specifies a time of day earlier by more than a predetermined amount than the present time of day as represented by the time-of-day data from the present time means to produce an output condition indicative of this condition.

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