Digital apparatus for magnetic media data recovery system

Abstract

A digital apparatus recovers data recorded in FM or MFM on a magnetic media moving at a normal speed in which the reading of the media provides a sequence of timing/data pulses at variable intervals, which differ from a nominal interval due to speed error and magnetic 'peak-shift'. The apparatus provides identification of a nominal interval between read out pulses and the reconstruction of a correct stream of pulses properly located within a window signal. It includes a digital measurement unit which at each read out pulse n received in input supplies at an output a code indicative of the actual duration of the interval N between the pulse n and a previous pulse n-1; and a speed correction unit which corrects the measured duration of the interval N relative to speed error detected by the digital measurement unit during reading of a synchronization bit field. A peak shift correction unit included within the apparatus utilizing the corrected interval duration, and for MFM recording, the previous most recent history of received pulses establishes a nominal duration for the interval N. The nominal duration attributed to interval N is used by a regeneration unit to produce a suitable window signal and a regenerated pulse corresponding to the read out n pulse which is properly located within the window signal.