Address mark detection circuit

摘要

An address mark detection circuit for use in a magnetic disk data storage unit is disclosed which features a Mealy sequential machine for providing a sequence of logical steps for the testing of sampled data in the search for an address mark; comparison between a given address mark and sampled data is eliminated. In a preferred embodiment, the specific mark to be detected is a first high frequency field followed by a second lower frequency field. The data is repeatedly sampled, and a digital frequency detector is used to provide a two bit signal to the sequential machine for stepping it in a direction corresponding to the frequency of the sample. The circuit allows elimination of means for detection of rotational position sensing information from a dedicated disk surface and elaborate phase-locked-loop circuitry for generating a data rate clocking signal in favor of simple and reliable logic circuitry.