| 摘要 |
PURPOSE:To detect an address mark without using any timer by delaying a detection signal as to the end of a synchronizing area through a shift register and determining the timing of address mark detection. CONSTITUTION:A signal 11 read out of a disk is inputted to a 16-bit shift register (SR)1 with a clock signal 12 and the output data signal 13 obtained by delaying the signal 11 by 16 clock pulses is inputted to a 16-bit SR2. A 32-bit comparator 3 compares the contents of the SR1 with the synchronizing area data pattern of the output 15 of the SR2 and sends a synchronizing area end signal 16 to a 15-bit SR4 on transition from coincidence to dissidence; and the comparison permit signal 17 obtained by delaying the signal by 15 clock pulses is sent from an SR4 to a 16-bit comparator 5, which compares the contents of the SR1 with the data pattern of a specific address mark, so that the address mark detection signal DET18 is outputted when the comparison result indicates coincidence.
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