| 摘要 |
<p>PURPOSE:To provide the synchronization protective circuit of a small circuit scale by outputting synchronization/asynchronization flags from a flag inversion part when a frame pattern is detected at a prescribed position and when it is not detected by a control condition output circuit. CONSTITUTION:Whether or not FP is detected at the prescribed position is judged by a frame pattern FP detection circuit 20, a master counter 21, a decoder 10 and the control condition output circuit 24. When the FP is detected at the prescribed position during a rear protective operation by the control of the circuit 24, a sub counter 22 is counted up. When the prescribed FP is detected at the prescribed position over (m) frames, it is defined that synchronization is attained and the circuit 24 sends a flag inversion signal to a flag inversion blade 23 and lets the synchronization flag outputted. Also, when the prescribed FP is not detected at the prescribed position over (n) frames in a synchronous state, it is defined that asynchronization is attained and the circuit 24 sends the flag inversion signal to the flag inversion part 23 and lets the asynchronization flag outputted. Thus, regardless of the number of frames, the synchronization protective circuit of the small circuit scale with two counters can be obtained.</p> |
