Programmable preamplifier unit with serial interface for disk data

Abstract

A disk drive preamplifier unit includes a serial interface circuit for receiving serially formatted control signals from an associated disk drive controller. The control signals contain several types of information, including head select, write current magnitude, bias for MR transducers, gain magnitude for a variable gain amplifier, and test and mode information. The preamplifier unit incorporates several test circuits in addition to the usual write unsafe detector circuit, and a multiplexer controlled by the mode control signals from the serial interface unit is used to select which test circuit or detector is coupled to a common test output terminal whose signals are coupled back to the controller for further processing. The preamplifier can be used to remotely test the head population of the head disk assembly, to measure the MR bias current through any of the MR transducers and to signal the controller in response to polling characters when a match is obtained between a character and preestablished multi-bit parameter information fixed in the preamplifier unit. A write current generator is shared by the write transducers and the MR bias test circuit, with a current scaling unit used to provide different current ranges from the common source. The preamplifier unit affords remote control and testing which can be adapted to evolving systems using firmware changes alone.