Abstract: Speech path switching control apparatus and a method for making maintenance of speech possible even upon occurrence of a fault in echo cancellation. The speech path switching control apparatus includes a time switch for receiving PCM voice data from a space switch through a switch network link and performing time slot interchange with trunk lines, an echo canceller connected to the time switch through a plurality of sub-highways to cancel echoes, an access switching processor for discriminating whether echo cancellation is required for a trunk call allocated with a particular one of the trunk lines and outputting the resultant discrimination signal, and a time switch control processor for controlling the time switch and the echo canceller in response to the discrimination signal from the access switching processor. If the echo cancellation is not required or the echo canceller is abnormal, there is formed a speech path which is not passed through the echo canceller.

Abstract: A circuit for determining whether a digital circuit clock is operating normally. It includes a monitoring clock receiver for receiving a monitoring clock signal, a counter reset generator which generates a first reset signal in response to the monitoring clock signal, and a reset signal receiver for receiving a second reset signal and synchronizing the second reset signal with the monitoring clock signal. The second reset signal is also used to initialize a digital circuit pack upon power-on. The circuit further includes a monitoring counter circuit for sampling and counting a reference clock signal in response to the first and second reset signals to monitor the monitoring clock signal. The reference clock signal has a frequency twice that of the monitoring clock signal. A NAND logic unit is provided for outputting the monitored result in response to an output signal from the monitoring counter circuit so that the user can determine a clock error according to the monitored result.

Abstract: A continuous-wave stabilizing apparatus wherein laser output power is stabilized by a feedback control of a voltage applied to an auxiliary electrode installed between an anode and a cathode depending on fluctuation of laser output power.