| 摘要 |
PURPOSE:To prevent the control operation of each section at lower-stages from a frame synchronization circuit from being stopped by providing a subframe counter to a frame counter applying a frame pulse to a coincidence detection circuit. CONSTITUTION:A coincidence detection circuit 15 being a component of a synchronization protection circuit 10 outputs a coincidence signal H when a frame pulse from a frame counter 14 is not in frame synchronization. On the occurrence of the noncoincident signal from the circuit 15, a counter stop control circuit 19 stops the frame counter 14 but does not stop a subframe counter 24, which continues the count in a same phase by self-loading to monitor the transmission of various control signals. When the frame pattern is detected, the output of the circuit 19 goes to an L level to allow the counter 14 to execute counting for starting backward protection, but the counter 24 continues counting synchronously with a new phase of the counter 14 to monitor the transmission of various control signals. |
