Apparatus for detecting regularly occurring signal sequence in a data stream.

摘要

A SYNC Detected signal (1035) is normally provided by resetting a flip-flop (1237) when a synchronization code in a header or data preamble of a disc sector is detected by logic (1223). Flip-flop (1237) is initially forced set by a signal (1229 or 1231) indicating a header or data preamble should be present. Detection of the code pulls SYNC DET (1225) low to reset the flip-flop (1237) and thereby force SYNC Detected high. If the code is not detected when it should have been, a signal SET SYNC (651) is forced low to reset another flip-flop (1251) which puts SYNCW (1219) low and puts SYNC Detected (1035) high via an inverter (1221). Accordingly data will always be read from a header preamble but the header will not be read correctly and will not match the target header. Data will therefore not be read from or written to the sector.