JPH05114252A - Magnetic disk device - Google Patents

Abstract

PURPOSE:To detect a fault so as to improve the positioning accuracy of a head by recording signals by using a servo pattern which is formed by adding dummy bits to gray codes and detecting an address error by counting the number of the dummy bits contained in reproduced signals. CONSTITUTION:At the time of detecting the position of a head arm 21, a sector servo pattern(SSP) recorded by adding dummy bits to gray codes on a magnetic disk 10 is reproduced and the position detection is controlled on the basis of obtained positional information. Reproduced signals from the SSP are inputted to an AGC equalizer circuit 231 through a head 21a and read/write circuit 22 and, of the information of the SSP, information regarding track addresses and information regarding tracking are supplied to a detection circuit 234 and pulse detection circuit 232. The circuit 232 discriminates the level of RF signals and supplies the discriminated level to a servo detection circuit 233. The circuit 233 discriminates the occurrence of an address error when the number of the dummy bits added to gray-like codes and contained in reproduced signals does not reach a specific number.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk device suitable for application to, for example, a magnetic disk device using a sector servo system.

[0002]

2. Description of the Related Art Generally, in a sector servo type magnetic disk, a sector servo pattern is arranged in the head area of each sector. An example of this sector servo pattern will be described with reference to FIG.

The head area in which the sector servo pattern of each sector is arranged is a data area D as various sector servo patterns shown in FIG. 5, and then AGC, servo header H, track address AD and so-called fine pattern are arranged in order from the head of the sector. FP is written. Further, a burst signal is recorded on the fine pattern FP as a servo signal for tracking control. The fine pattern FP divides the three servo signals A, B and C into regions F _A , F _B and F _C. In particular, the servo signals A and B are offset from each other in opposite directions to the track, and the fine patterns A and B are recorded in a so-called checkered pattern. Further, in the fine pattern C, a predetermined reference signal is continuously recorded.

A magnetic disk head has a width T shown in FIG.
_W is scanning the sector servo pattern. Above AGC
The area is the automatic gain control (A
It is provided to converge the gain of the GC) circuit. The servo header H is provided for recognizing that it is a servo pattern, and serves as a time reference for generating the timing of pattern detection after the servo header. The AGC and the servo header H are continuously written in the radial direction. Further, the track address AD, together with the data area D, has position information written at the center position of each track. For example, in FIG. 5, tracks AD _{1 to} A
₅ tracks up to D ₅ are shown.

The fine pattern FP indicates position information by a servo signal for the head track. The fine patterns A and B are alternately arranged in a checkered pattern with the track pitch T _P / 2 offset in the opposite direction with respect to the center of each track, and the fine patterns A and B are scanned in accordance with the detected head position. The envelope of changes. The displacement of the head is detected by detecting the changing envelope. Unlike the fine patterns A and B, the fine pattern C is recorded so as to continuously output a constant envelope level in the radial direction.
This fine pattern C is used to normalize the level. The position signal of the head, the fine pattern when the head is scanned A, B and C levels V _A of the burst signal, with the V _B and _{V C (V A -V B)} /
It can be _calculated from V _C. After this, the data area is arranged.

The track address AD described above indicates a coarse positioning signal. A graylike code is used for the coarse positioning signal. The Gray-like code is
word) is a code that is further encoded by using an alternating binary code (Gray code) having a Hamming distance between two adjacent quantization levels as 1 as source data. For example, a continuous 2-bit gray code, that is, (0
0), (01), (11) and (10) are converted into 2 to 3 channel bits (001), (010), (10)
0) and (111) are used. The Gray-like code in this case has a Hamming distance of 2 due to the encoding by the 2-3 conversion. Since each code word includes "1", the so-called run length, which is a run of "0" s, is limited. It also satisfies the requirement that the magnetization directions are the same between adjacent tracks.

The applicant of the present application has proposed a track address pattern of a magnetic disk device in the specification and drawings of Japanese Patent Application No. 02-130745 dated May 21, 1990. In this prior application technology, the gray-like code is used for the track address of the magnetic disk to increase the code rate of the track address and reduce the ratio of the address pattern so that more data can be recorded than normal data. Shows that it can be increased and is beneficial. The above gray-like code, when the head passes the boundary of the adjacent code,
Even if one undetectable pulse occurs, it is always decoded into one of the address values to shorten the access time.

The actual head position control using the gray-like code by the above-mentioned 2-3 modulation will be described. A specific example of the gray-like code by 2-3 modulation will be described. Two bits of the gray code, that is, (00), (01), (11) and (10) are converted to (00
1), (010), (100), (111) are not limited to the conversion method corresponding to, for example, 2 bits of the Gray code, that is, (00), (01),
(11) and (10) are exclusive OR inversion circuits (Exclude
sive NOR) and input this output to the gray code 2 above.
There is also a method of inserting between bits to perform 2-3 conversion. As a result, three channel bits (010) and (00
1), (111), and (100) are generated. This gray-like code is written in the servo pattern. The gray-like code detection method uses a hysteresis type threshold detector in a pulse detector for generating a read pulse in a magnetic disk device. The pulse detector sets the threshold levels on the positive side and the negative side, respectively. By using these two threshold levels, "1" of the Gray-like code is detected and the magnetization is inverted while performing the hysteresis operation.

[0009] New codes such as the Gray-like code having such a feature and having a higher conversion rate have been actively researched.

[0010]

By the way, under the above-mentioned conditions for detecting the read pulse signal, for example, an error corresponding to a read pulse E _b1 described later in which the detection signal of the supplied data "1" does not exceed the threshold value occurs. In this case, as shown in the output waveform of the low-pass filter shown in FIG. 6, the pulse detector detects not only the error corresponding to the read pulse E _b1 but also the data “1” which exceeds the threshold.
The read pulse E _b2 corresponding to is also undetectable. This is because the pulse detector has a hysteresis type, and thus the former read pulse cannot be detected even if the threshold level is accurately exceeded by the latter data "1" corresponding to the read pulse E _b2. This is because the history pulse and the output latter pulse have the same polarity, and the above-described impossible two consecutive output waveforms result in control not to detect a pulse.

A specific example of the generation of error bits due to the gray-like code data will be described with reference to FIG. FIG. 6A shows a gray-like code with adjacent 2-3 transforms. The magnetization reversal pattern on the recording medium based on the gray-like code data is shown in FIG. 6B.
Is shown in. That is, N → S or S → N magnetization reversal is performed corresponding to the gray-like code data “1”. The gray-like code has a Hamming distance of ± 1, so that even if the head scans between adjacent tracks, one of the addresses is always obtained. Also, FIG. 6C
When the head passes the position of the arrow shown in FIGS. 6A and 6B, that is, the boundary between adjacent codes, the output waveform of the low-pass filter alternately has polarities corresponding to the rising edge of the gray-like code data. It shows how to invert. 6D and 6E respectively show a read pulse obtained by level-discriminating the output waveform of the low-pass filter with hysteresis at the slice levels provided to the positive and negative sides, and reproduced data corresponding to the read pulse.

When the head passes the boundary between the gray-like codes adjacent to each other at the arrow positions shown in FIG.
When divided into bit-by-bit cells, they are adjacent to each other (01
Although there is data "1" in the cells of (0) and (001), no read pulse is generated in the shaded portion of FIG. 6C because the slice level on the negative side is not exceeded, that is, the first error bit. It becomes E _b1 . Next, "1" can be detected at the boundary between the above (010) and the next data (100) +
Even if the output waveform exceeds the side slice level, the second read pulse E _b2 is not generated because the polarity is the same as the polarity of the slice level at the output of the immediately preceding read pulse.

Thus, the pulse detector produces two consecutive errors with one error occurring at adjacent boundaries. Therefore, the magnetization pattern based on the read pulse data output from the pulse generator is a pattern quite different from the magnetization pattern on the recording medium. This pattern is not decoded by any of the adjacent codes.

By the way, even when a defect occurs in the address information by the Gray-like code, two consecutive data at the position where the data "1" is output are erroneous as in the case where the head passes the boundary between adjacent codes. .. However, it may not be possible to easily determine whether this error is due to the fact that a defect has actually occurred in the recording medium or due to the fact that the head has passed the boundary between adjacent codes.

Therefore, the erroneous servo information cannot be determined as erroneous detection, and the position of the head is controlled based on the erroneous servo information to control the position of the head at a position different from the target position. It will be. As a result, by repeatedly applying the servo for position control while this influence is added as a new disturbance in the position control of the head, it takes time for the hard disk to access and control the drive of the head to the target position.

In view of the above situation, it is an object of the present invention to provide a magnetic disk drive capable of detecting a defect existing in a servo pattern of a recording medium.

[0017]

A magnetic disk device according to the present invention is a magnetic disk device using a sector servo system, wherein a plurality of bits of gray code corresponding to a servo address of a sector servo pattern are divided into groups of 2 bits, The 2-bit group divided into groups is (001), (010), (1
00) or (111) converted into a 3-bit code, the dummy-like code is added and recorded, and the dummy bit added to the gray-like code in the reproduction signal is counted to a specified number. The above-mentioned problem is solved by setting an address error when it does not reach.

In the method for detecting the gray-like code, a pulse detector for generating a read pulse in a magnetic disk device uses a hysteresis type threshold level detector. The pulse detector sets the threshold levels on the positive side and the negative side, respectively. Using these two threshold levels, "1" of the Gray-like code is detected to perform magnetization reversal, N → S, or S → N while performing a hysteresis operation.

The specified number of counted dummy bits can be determined by counting the number of undetectable dummy bits. When one of the dummy bits cannot be detected at the time of so-called on-track where the head is located at the track center, it is assumed that a defect has occurred in the recording medium. Further, at the time of seek, if at least two undetectable dummy bits are detected, it is determined that a defect has occurred and an address error flag is set, for example.

[0020]

The magnetic disk device according to the present invention counts unnecessary dummy bits in the reproduced signal and counts them, for example, less than the number specified by the user (or more than the undetectable number specified by the user). At this time, an error flag is set to the address pattern of the sector in which the defect in the recording medium is detected, and the destruction of the servo address is detected.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a magnetic disk device according to the present invention will be described with reference to the drawings.

The magnetic disk device of the present invention has a pulse detector for generating a read pulse in the magnetic disk device. This pulse detector uses a detector whose threshold level is a hysteresis type. The pulse detector sets the threshold levels on the positive side and the negative side, respectively. By using these two threshold levels, "1" of the Gray-like code is detected and the magnetization is inverted while performing the hysteresis operation.

Here, the magnetic disk device uses, for example, a sector servo system. This sector servo system is
The position of the head is controlled by the servo address indicating the coarse positioning information of the sector servo pattern arranged at the head position of each sector.

First, a method of erroneously detecting a servo address by using a Gray-like code as the servo address used for the address pattern of the magnetic disk device and further adding a dummy bit will be described. For example, when the read head crosses the boundary between two adjacent tracks during a high speed seek, a bit that can take either a value of "1" or "0" appears. When this bit is represented by "x", the reproduced channel data includes two "x" s. When the read data is (0xx), the converted data means (001) and (010).
When (xx0), the converted data is (010),
This means (100), and when (1xx), the converted data means (100) and (111). That is, the reproduced address may include an error of ± 1 track with respect to the target address.

As described above, when the head passes through the boundary between the adjacent codes, the magnetic field of the first error bit E _b1 which is accidentally generated by the influence of the magnetization reversal polarity does not cause any defect even if there is no defect. The error bit E _{b2 of 2} is generated (see FIG. 6).
See).

Therefore, a method is used in which dummy bits are added to the gray-like code and recorded in the servo address information in the sector servo pattern. FIG. 1A shows a code obtained by further encoding, as source data, an alternating binary code (Gray code) having a Hamming distance of 1 between two quantization levels in which each code word is adjacent. For example, a continuous 2-bit gray code shown in FIG. 3, that is, (00), (01), (11)
And (10) are converted to 2-3 and three channel bits (00
1), (010), (100), and (111). For example, a dummy bit D is added to the end of each cell, that is, the least significant bit, for these three channel bits for one cell.
_The state where _b is added is shown. Therefore, each cell has 3
By adding the channel bits and the dummy bits, it is composed of 4 channel bits.

By adding the dummy bit for preventing erroneous detection, even if the data E _b1 is lost due to the first defect when the head passes through the adjacent servo address boundaries as shown in FIG. 6, If the data at the position of the dummy bit D _b is ignored when decoding the read data by associating the second error bit E _b2 with the dummy bit D _b , only the first error bit E _b1 is detected. Disabled,
One error can be absorbed without erroneously detecting the data of the next cell C ₄ .

The method of correcting the first error bit is the 3-bit channel data (B2, B1, B0).
When the source data (A1, A0) is decoded from, the following two relational expressions (1) and (2) can be derived from FIG. A1 = B2 (1) A0 = (inversion of B0) (2) Therefore, the source data can be directly obtained from the bit 2 (B2) and the bit 0 (B0) of the channel data. In this way, the ambiguous address information is confirmed.

In the magnetic disk device of the present invention, when the address information is actually defective, this defect (defect)
The detection method of will be described with reference to FIGS. 1 and 2. The magnetic disk device of the present invention distinguishes between the two states, on-track and seek, to detect whether or not the recording medium actually has a defect in the address information. Method of detecting the defect (defect), the head track center focused on the dummy bit D _b, i.e. during the so-called on-track, if counted the dummy bit D _b is one less than the predetermined number, a recording medium Defects (defec
t) is considered to have occurred. In other words, if one of the dummy bits D _b cannot be detected, the address is destroyed.

FIG. 1 shows a case where a gray-like code is used for an address pattern and dummy bits are added. FIG. 1A shows a gray-like code by adjacent 2-3 conversion when the head is on track.
A magnetization reversal pattern on the recording medium based on the gray-like code data is shown in FIG. 1B. That is, N → in response to input of gray-like code data “1”
The magnetization reversal of S or S → N is performed. Also, FIG.
C is a state in which the output waveform of the low-pass filter alternately inverts the polarity in response to the rising edge of the gray-like code data when the head passes over the track at the data position shown in FIGS. 1A and 1B. Is shown. FIGS. 1D and 1E respectively show a read pulse obtained by discriminating the output waveform of the low-pass filter with hysteresis at the slice levels provided to the positive and negative sides, and reproduced data corresponding to the read pulse. It also indicates that there is a missing read pulse at the position indicated by the dotted line in FIG. 1D.

[0031] If a defect occurs in the first bit position of the cell C ₃ indicated by the arrows in Figure 1B, the cell C ₃ shown in FIG. 1C
A waveform having a hysteresis and exceeding the slice level is output only at the position of the dummy bit D _b . However, as described above, the dummy bit D _b of the cell C ₃ is also lost due to the influence of hysteresis. Conversely, the dummy bit D _b always, from the condition that is to generate a read pulse, not to generate a read pulse to the position of the dummy bit D _b is
It means that there is a defect in the cell and the generation of the next read pulse is suppressed.

By considering in this way, it is possible to easily detect the loss of the dummy bit D _b of the signal during on-track.

However, when the head passes through the boundary between the adjacent gray-like codes as described above when the head seeks, the dummy bit D _b may be undetectable even if there is no actual defect. .. The detection of a defect when the head seeks will be described with reference to FIG.

FIG. 2B shows a magnetization reversal pattern on the recording medium based on the Gray-like code data shown in FIG. 2A. That is, the magnetization reversal of N → S or S → N is performed corresponding to the input of the gray-like code data “1”. Further, FIG. 2C shows that when the head passes the boundary between the adjacent codes, the output waveform of the low-pass filter alternately inverts the polarity in response to the rising edge of the gray-like code data. FIGS. 2D and 2E show that when the output waveform of the low-pass filter exceeds the positive and negative slice levels, a read pulse is set at each detection point and the data read from the recording medium is determined according to the read pulse. ing. FIGS. 2D and 2E show the case where the address data is not lost even if an error may occur when the head passes the arrow position shown in FIG. 2B. 2F
1G and 1G show the case where the actual address data is missing.

When the head passes through the boundary of the adjacent gray-like codes shown in FIG. 2A by dividing the data into cells C _{1 to} C ₅ for every 4 bits, the output waveform of the low pass filter of FIG. 2C has a magnetization reversal. Depending on the direction of the position, the pulse has a positive polarity or a negative polarity.

In the cell C ₂ shown in FIG. 2A, the head passes through the boundary between the adjacent gray-like codes in the cell C ₂ , so that the mismatched portion of the magnetization reversal pattern of FIG. 2B is detected as an error bit. The channel data at this position does not exceed the slice level as shown by the output waveform LO ₁ of the low pass filter in FIG. 2C. By passing through the boundary of the adjacent gray-like code at the time of seek, the read pulse shown in FIG. 2D is dropped as in the case of FIG. 1, and the first error bit E of the cell C ₂ shown in FIG. 2E is lost. _A pulse cannot be output to the position of _b1 and cell C
_This shows a situation where one dummy bit D _{b of 2} cannot be detected.

A description will be given with reference to FIGS. 2F and 2G when a defect actually exists in a servo address at the time of seeking through the boundary between the adjacent gray-like codes. In the cell C _{2 of} FIGS. 2F and 2G, the dummy bit E by passing through the above-mentioned boundary is provided.
It also shows that _b2 (= D _b ) is undetectable (see FIGS. 2D and E). In addition, for example
_{When the} defective bit E _def exists at the first position of ₃ , the dummy bit E _b3 added to the cell C ₃ similarly occurs.

When the servo address is destroyed due to the presence of the defect thus generated on the recording medium and the head passes the boundary between the adjacent gray-like codes at the seek time,
At least two or more dummy bits D _b may become undetectable.

As described above, when the head is at the center of the track, that is, when the track is on-track, the dummy bit D _b is 1
If one becomes undetectable, it means that a defect has occurred. Also, during seek, dummy bit D
_If at least two of the above-mentioned undetectable specified numbers are detected in _b, it is assumed that a defect has occurred. By detecting the presence / absence of a defect according to such a condition, it becomes possible to accurately detect the defect of the servo pattern.

A structure for accurately detecting a defect in the servo pattern will be described with reference to the schematic block diagram of the magnetic disk device shown in FIG. The magnetic disk device controls the position of the head based on the RF signal when the sector servo pattern is scanned. In brief, this magnetic disk device has a spindle motor 20, a head 21a at the tip of a head arm 21 which is a part of an actuator, a read / write circuit 22, a head position detector 23, a RAM 24, a digital signal processor (DS).
P) 25, voice coil motor (VCM) drive circuit 26
And voice coil motor 27. The recording medium recorded / reproduced by this apparatus is, for example, the magnetic disk 10
Is used. The magnetic disk 10 is divided into dozens of sectors in the circumferential direction. Information such as address information and fine pattern necessary for positioning of each sector is written in the sector servo pattern (SSP). Positioning control is performed according to the information from this sector servo pattern.

Further, the head position detecting section 23 includes an automatic gain control (AGC) / equalizer circuit 231, a pulse detecting circuit 232, a servo detecting circuit 233, an envelope detecting circuit 234, an A / D converter 235, and a CPU 236.
And a D / A converter 237.

The operation of the above block configuration will be briefly described along the flow of signals. When detecting the position of the head arm 21, the sector servo pattern (SSP) written on the magnetic disk 10 which is a recording medium is reproduced, and position detection control is performed based on the position information obtained from this sector servo pattern (SSP). It is carried out. A reproduction signal from the sector servo pattern (SSP) is supplied to the read / write circuit 22 via the head 21a at the tip of the head arm 21 which is a part of the actuator.

The read / write circuit 22 amplifies the reproduction signal and sends it to the automatic gain control (AGC) / equalizer circuit 231.

The automatic gain control (AGC) / equalizer circuit 231 detects the information on the track address AD and the information on the tracking of the head 21a by the burst signal from the fine pattern FP from the information on the sector servo pattern, and detects the information. The pulse detection circuit 2 is supplied to the envelope detection circuit 234 and
Supply to 32.

The pulse detection circuit 232 determines the level of the RF signal with respect to the positive and negative slice levels with hysteresis and supplies it to the servo detection circuit 233. The servo detection circuit 233 checks whether the input signal is a servo pattern, identifies the area, and outputs the detection signal to the envelope detection circuit 234. The output signal from the AGC / equalizer circuit 231 is detected by the envelope detection circuit 234 according to the timing of the detection signal. The detection output from the envelope detection circuit 234 is supplied to the A / D converter 235. A / D converter 23
Reference numeral 5 converts data sampled in accordance with a signal synchronized with a system clock, for example, into a digital amount, and supplies the digital amount to a digital signal processor (abbreviated as DSP hereinafter) 25 via a 16-bit DSP bus. Also supplies. Further, the data is read into the CPU 236 according to the read signal from the CPU 236. CPU 236
Supplies a signal corresponding to the control data for calculating the servo amount for position detection to the DSP 25. Further, the DSP 25 performs, for example, a calculation for correcting an external force applied to the head, and the signal obtained by correcting the external force and the CPU
The signal supplied from 236 is added to the D / A converter 23.
The output is 7.

In this way, the control signal corresponding to the servo amount for position detection is sent from the head position detector 23 through the low pass filter (not shown) to the voice coil motor (VCM).
It is supplied to the drive circuit 26. The voice coil motor drive circuit 26 sends a drive control signal corresponding to the supplied control signal to the voice coil motor 27 to perform position control.

In the magnetic disk device of the present invention, the number of dummy bits added to the gray-like code in the reproduction signal by the servo detection circuit 233 shown in FIG. 4 does not reach the specified number (or the number of dummy bits that cannot be detected is increased). Address error is detected when more than the specified number is detected.
At this time, the DSP 25 shown in FIG. 4 determines whether the head is on the track center, that is, when the track is on or when seeking.

When the DSP 25 determines that the track is on, if the count number of the dummy bits D _b is one less than the specified number, it is determined that the data in the servo address is destroyed and the address error flag is set. Stand up.
Further, when the head passes a boundary between adjacent tracks at the time of seek in the DSP 25, the number of dummy bits D _b is specified in consideration of the number of dummy bits D _b which cannot be detected even if there is no defect in address information. If it is at least two less than the above number, it is determined that the data in the servo address is destroyed and an address error flag is set. In this embodiment, when the dummy bits _Db are 2 bits or more, it is determined that a defect has occurred and an address error flag is set.

As described above, the address error flag is set to easily detect the destruction of the servo address due to the defect, and the position control by the sector servo is performed without using the position information of the sector where the defect error occurs.
Therefore, the magnetic disk device can suppress the influence on the servo system, such as the disturbance of the servo control, which has been caused by the defect in the positioning. Also,
Thereby, for example, a delay in head position detection can be avoided.

[0050] The data of the servo address in the embodiment described above has been detected defects make a address error flag for two or more bits of the missing dummy bit D _b, the address pattern of the above-described magnetic disk unit It is also possible to detect the defect by setting a standard for the defect in the other area and corresponding to the error.

[0051]

As is apparent from the above description, according to the magnetic disk device of the present invention, in the magnetic disk device using the sector servo system, the gray code of 2 bits corresponding to the servo address of the sector servo pattern is set to 2 bits. Each bit is divided into groups, and each group of 2 bits is divided into (00
1), (010), (100) or (111) converted into a 3-bit code, the dummy-like code is added to the gray-like code and recorded, and the dummy bit is added to the gray-like code in the reproduced signal. By determining the address error when the number is not reached to the specified number, the destruction of the servo address can be easily detected according to the operating condition of the head. The detected sector servo information is not used for head position control, but the head position control can be performed at high speed and with high accuracy from other sector servo information, for example.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a principle of detecting a missing servo address during on-track in an embodiment using an address pattern of a magnetic disk device according to the present invention.

FIG. 2 is a diagram illustrating a principle of detecting a missing servo address at the time of seeking using an address pattern of a magnetic disk device.

FIG. 3 is a diagram showing a relationship between channel data and reproduction data when 2-bit Gray code which is source data is converted into 2-3.

FIG. 4 is a schematic block diagram showing a circuit configuration in a magnetic disk device of the present invention.

FIG. 5 is a diagram showing an example of an actual sector servo pattern written on a disk.

FIG. 6 is a diagram illustrating a relationship between error positions that occur in a conventional Gray-like code.

[Explanation of symbols]

D _b・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Dummy bits C _{1 to} C ₅・ ・ ・ ・ ・ ・ Cells LO ₁ and LO ₂・ ・ ・ ・ ・ ・ ・ ・ Low pass filter output waveform E _b1 , E _b2 , E _b3 ··· Read pulse error bit E _def ····· Missing bit

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[Procedure amendment]

[Submission date] April 15, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0045

[Correction method] Change

[Correction content]

The pulse detection circuit 232 determines the level of the RF signal with respect to the positive and negative slice levels with hysteresis and supplies it to the servo detection circuit 233. The servo detection circuit 233 checks whether the input signal is a servo pattern, identifies the area, and outputs the detection signal to the envelope detection circuit 234. The output signal from the AGC / equalizer circuit 231 is detected by the envelope detection circuit 234 according to the timing of the detection signal. The detection output from the envelope detection circuit 234 is supplied to the A / D converter 235. A / D converter 23
Reference numeral 5 converts the sampled data into a digital amount according to a signal synchronized with the system clock, for example, and supplies the digital amount to a digital signal processor (abbreviated as DSP hereinafter) 25 via a 16-bit DSP bus.
Here, the DSP 25 generates a signal corresponding to the control data in which the servo amount for position detection is calculated. Also, DS
P25 performs, for example, a calculation for correcting the external force applied to the head, adds the external force corrected signal and the control data , and outputs it to the D / A converter 237.

Claims (1)

[Claims] 1. A magnetic disk device using a sector servo system, wherein a plurality of bits of gray code corresponding to a servo address of a sector servo pattern are divided into groups of 2 bits,
A dummy bit is added to a gray-like code obtained by converting the grouped 2-bit group into a 3-bit code of (001), (010), (100) or (111) according to each value. And record
A magnetic disk device characterized in that an address error is generated when the number of dummy bits added to the gray-like code in the reproduction signal is counted and the prescribed number is not reached.