Sector mark decoder for an optical recorder

Abstract

Disclosed is a sector mark decoder for an optical recorder. Sector marks are prerecorded on the optical recording surface and comprise a series of evenly spaced marks. Data is recorded on the media in a fixed block code via holes burned into the optical recording surface. Both sector marks and data are detected by common apparatus, but are distinguished from each other by their different recording format. The location of a hole or a prerecorded mark is determined by comparing two sample and hold cells in a comparator. One holds the read signal value received at one disk position and compares it to the signal value held in the other sample and hold cell received at the previous position. If the comparison results in a new higher valued signal being found, the output of the comparator changes. The new higher valued signal is retained and the other sample and hold cell samples at the next disk position. This sequence continues until a sector mark has been decoded. If the output of the comparator changes, the 'address' of the change is recorded. A sequencer determines from the 'addresses' of a series of holes or prerecorded marks that a sector mark is being detected, and issues a sync pulse. If the sequence of 'addresses' does not correspond to a sector mark sequence, data holes are being read and a sync pulse is not issued.