Kabushiki Kaisha Toshiba

Hiroshi Suzuki

Koji Osafune

A data separator system has a PLL circuit for out-putting data pulses and clock pulses on the basis of the read data from a magnetic recording medium. The system also includes an external synchronization detection circuit which detects the synchronization data (predetermined zero pattern data) recorded in the synchronization area of the magnetic recording medium, on the basis of the read data. When detecting the synchronization data, the synchronization detection circuit enables the PLL circuit to oscillate in synchronism with the read data. The data pulses and clock pulses output from the PLL circuit are also supplied to an internal synchronization detection circuit. On the basis of the data pulses and the clock pulses, the internal synchronization detection circuit detects the synchronization data, and upon detection thereof, a floppy disk controller performs the data readout operation. The system further comprises a preventing circuit which prevents the PLL circuit from performing the synchronizing operation to the read data, which is read out from the overwritten area in the magnetic recording medium by the preceding-erase type magnetic head.

Recording/reproducing system for a magnetic recording medium including

A recording/reproducing system is provided with a PLL circuit for outputting data pulses and clock pulses on the basis of the read data reproduced from a magnetic recording medium. An external synchronization detection circuit is provided which detects the synchronization data (predetermined zero pattern data), recorded in synchronization areas of the magnetic recording medium, on the basis of the read data. When the synchronization data is detected, the synchronization detection circuit enables the PLL circuit to oscillate in synchronism with the read data. An internal synchronization detection circuit is provided, which detects the synchronization data (predetermined zero pattern data), as recorded in the synchronization areas of the magnetic recording medium, on the basis of data pulses derived from the PLL circuit and the clock pulses. A preventing circuit is further provided. When address mark data is not detected within a predetermined period of time after the external synchronization detection circuit detects th synchronization data, the preventing circuit prevents the PLL circuit from oscillating in synchronism with the read data.

A magnetic disk apparatus has a magnetic head in contact with a flexible magnetic recording medium, for reading out data stored in the recording medium. The magnetic head of the apparatus is of the preceding-erase type. A converting circuit converts the output signal of the magnetic head to digital read data, and outputs it to the PLL circuit. The magnetic disk apparatus includes a preventing circuit for preventing the converting circuit from outputting to the PLL circuit the digital read data which corresponds to read out data from the DC erased areas in the tracks of said magnetic recording medium. The preventing circuit comprises an AGC amplifier for amplifying the signal read out of the magnetic head, a circuit for obtaining an envelope of the output signal of the AGC amplifier, and a circuit for preventing the converting circuit from outputting the read data when the signal level of the envelope is lower than a predetermined value.

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Monroeville, PA, United States of America

Hiroshi Suzuki