JPH0223946B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic disk device, and more particularly to a magnetic disk device that records information using a format method in which the length of a record, which is a recording unit when recording information on a magnetic disk, is variable. Regarding.

There are two recording formats for recording information on magnetic disks in magnetic disk devices: the sector format, in which the length of a physical recording unit called a record is fixed, and the format format, in which the length is variable. Which of these methods to adopt is determined as one of the design conditions of the magnetic disk device.

Among these, the recording format of the format method is as shown in Fig. 1, an example of which is that the home address (indicated as HA in Fig. 1) is followed by multiple records _R0 to R _o.
is recorded with a gap G between them,
Each record R ₀ ~ R _o starts with address mark AM,
Gap G and identification code ID are recorded, followed by data. When reading these, the start of each record is determined by detecting both AM and ID. However, a method is used in which subsequent data reading is performed based on this determination. For this reason, when AM or ID cannot be detected due to noise or other disturbances, data is not read out, which may cause what is called a record dropout.

This type of record omission can be detected by reading the record number recorded in the data of the next record in the case of the first or intermediate record, but in the case of the last record, there is no record following it. Unable to detect missing records,
Since the final record is judged and processed as if it had never been recorded, there is a risk that important data may be lost. (The beginning of the data in each record in the format system records basic information about that record, such as the record number, address, and data length.) Therefore, the fact that the data was recorded in the final record by some means. If this can be grasped, the data of this final record can be read by re-reading or other means, and loss of data can be prevented, resulting in a highly reliable magnetic disk device.

The present invention proposes means for achieving the above-mentioned object, and the number of pulses of a data pulse signal generated from a read signal of data modulated with the number of clock pulses serving as a reference for reading data is It is an object of the present invention to provide a highly reliable magnetic disk device that prevents record omission by providing a means for detecting the existence of a record by taking advantage of the fact that these signals are not equal and by counting and comparing the number of pulses of these signals. This is the purpose.

The magnetic disk device of the present invention includes a first counting circuit that inputs a clock pulse signal, which is a reference signal for reading data, and counts the number of pulses of the clock pulse signal according to a read command, and a first counting circuit that corresponds to the peak of the data read waveform. a second counting circuit that inputs a data pulse signal that generates pulses and counts the number of pulses of the data pulse signal in response to a read command; and A comparator circuit receives input and detects the difference between the number of pulses of the clock pulse signal and the number of pulses of the data pulse signal, and an output signal of the comparator circuit is input and stored, and a read command from a host device is input. and a storage circuit that outputs the stored signal.

The present invention will be described in detail below with reference to the drawings.

Figures 2a and b show the clock signal and the MFM method (a type of magnetic recording method), which records by reversing the direction of the write current between "1" and "0". FIG. 2 is a diagram showing readout waveforms of written data and waveforms of signals obtained by converting them into pulse signals (abbreviated as pulse waveforms).
As shown in the figure, the pulse waveform of the clock signal has an evenly spaced time interval of T, while the pulse waveform of the data signal has three types of intervals: T, 1.5T, and 2T. is a combination of
The number of pulses of the clock signal and the number of pulses of the data signal within the same time have different values. Similar to most other recording systems, the number of pulses of the data signal is generally either larger or smaller than the number of pulses of the clock signal, and is never equal to the number of pulses of the clock signal.

The present invention utilizes such a phenomenon to recognize the presence of a data signal by detecting the difference between the number of pulses of the clock signal and the number of pulses of the data signal within a predetermined readout time, and detects the presence of the data signal. FIG. 3 shows a block diagram of an embodiment of the present invention.

In FIG. 3, counting circuits 2 and 4 each receive a clock pulse signal 102 and a data pulse signal 104, receive a read command 106, count the number of pulses, and compare the counted values as counted value signals 108 and 110. The signal is sent to circuit 6. Comparison circuit 6 receives count value signals 108 and 110
is input, the difference is calculated, and the result is sent to the storage circuit 8 as a comparison signal 112. Storage circuit 8
inputs the comparison signal 112 and sends the stored calculation results to the host device.

The magnetic disk device configured as described above operates as follows.

When a data read operation is performed in a magnetic disk device, a clock pulse signal 10 is generated from the read waveforms of the clock signal and data signal read from the servo head and the data head.
2 and data pulse signal 104 are input to counting circuits 2 and 4, respectively, and at the same time, a read command (see FIG. 1) 106 is also input to counting circuits 2 and 4.

Counting circuits 2 and 4 receive the clock pulse signal 10 at the time specified by this read command 106.
2 and the number of pulses included in the data pulse signal 104 and sends the value as count value signals 108 and 110 to the comparator circuit 6. The comparator circuit 6 receives the count value signals 108 and 110 and calculates the number of pulses. Calculate the difference and compare the results with the signal 112
It is sent to the storage circuit 8 as a.

The storage circuit 8 receives and stores this comparison signal 112 sent from the comparison circuit 6, and when it receives the sending command 114 from the host device, it sends the stored calculation result to the host device. By receiving this and determining whether the comparison results are equal or larger, it is possible to recognize whether the record exists or not, and therefore it is possible to determine whether a record is missing. ,
When a record is missing, it is possible to read the record by rereading or other means, thereby preventing record omission.

As described above in detail, by using the magnetic disk device of the present invention, there is an effect that a highly reliable magnetic disk device that prevents record omissions can be obtained.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the recording format using the format method. FIGS. FIG. 3 is a block diagram showing one embodiment of the present invention. In the figure, 2, 4...counting circuit, 6...comparison circuit, 8...storage circuit.

Claims (1)

[Claims] 1. A first counting circuit that inputs a clock pulse signal, which is a reference signal for reading data, and counts the number of pulses of the clock pulse signal in response to a read command; a second counting circuit which inputs a pulse signal and counts the number of pulses of the data pulse signal in response to a read command; A comparison circuit that detects the difference between the number of pulses and the number of pulses of the data pulse signal, and an output signal of the comparison circuit is input and stored, and a read command from a host device is input and the stored signal is output. What is claimed is: 1. A magnetic disk device comprising: a storage circuit for storing data;