JP2760801B2 - Magnetic disk drive - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing erroneous writing of a magnetic disk drive, and more particularly to an interface in which a true value is at a LOW level and write data is inverted at a constant cycle. (Example ST50
It is suitable for the magnetic disk device used in 6).

[Conventional technology]

As an example of preventing erroneous writing of a storage device, see JP-A-60-740.
As described in Japanese Patent Publication No. 61, when power supply is interrupted, erroneous writing is prevented by power supply from a backup battery. Further, Japanese Patent Application Laid-Open No. 62-214575 describes a method of forcibly stopping a write operation after detecting an erroneous write on a magnetic tape so as to prevent further erroneous write.

[Problems to be solved by the invention]

In the above prior art, although a measure to be taken when the power supply of the device is interrupted is shown, when the power supply of the higher-level device connected to the device is cut off, an erroneous instruction is generated because the device is continuously supplied with power. No consideration is given to the fact that the device will receive it (Japanese Patent Application Laid-Open No. 60-74061). Further, although a method for preventing the spread of erroneous writing after occurrence of erroneous writing is described, no consideration is given to preventing it from occurring (Japanese Patent Application Laid-Open No. 62-214575). In addition, a method of detecting a flyback voltage at the time of writing generated in a magnetic head mounted on a disk device and suppressing an abnormal writing operation based on the presence or absence of inversion of write data is a known conventional technique. It is necessary to confirm data inversion of a certain amount or more due to variations in the characteristics of the magnetic head and the like, and it is difficult to prevent erroneous writing at the data unit level. An object of the present invention is to judge that an erroneous write instruction is different from an original normal instruction, and to prevent an erroneous write operation inside the device in units of data.

[Means for solving the problem]

At the time of receiving a write command sent from a higher-level device, the continuity of write data transmitted simultaneously on another interface line, and the period at the theoretical level, and the time set for the reference time determined by the interface specifications Monitor using a generator circuit. When the write data is out of a certain condition determined by the interface specifications, it is determined that the write command transmitted from the higher-level device is a sporadic erroneous write command at the same time. Stop using it,
Used only when certain conditions are satisfied as described above.

[Action]

MFM data is transmitted from the host device to the write data line in the ST506 interface. In MFM data, level inversion is always performed, and the cycle is limited to three types. Therefore, if a period in which data inversion is out of the above-mentioned regularity (short or long) even if a write command is issued, it is determined that there is an abnormality. Since the signal handled by the present invention is at a theoretical level, the reference cycle for determination can be set more easily than the interface specification.

When the write data is fetched by the shift register and reaches a certain value, a write command in the disk device is issued for the first time. In addition, the period of the write data to be taken into the register is monitored using a monostable circuit having three types of set times corresponding to the three types of regular periods. Except for the above-mentioned regular period, it is excluded as an input to the register. . As a result, an erroneous write command at the time of occurrence of write data that occurs sporadically and does not match the regular cycle of MFM data or accidentally occurs at the time of occurrence of sporadic write data that matches the regular cycle of the MFM data, Can be suppressed.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIG. 1 and FIG.

In FIG. 1, IF WT GT-N is a write command signal on the interface, IF MFM WT DT-P and the same N are
5 shows a write data signal. The true level of the interface is “LOW” level. When the power of the magnetic disk device is turned off while the power of the magnetic disk device is turned on, the IF WT GT-N line becomes the O level, that is, the true level, and the b line of the receiver output is output. Is a true value, albeit sporadically. Similarly, IF MFM WTDT
Since -N and the same P line also go to OV, a pulse having an irregular period is also generated on the receiver output line a.
When the circuit according to the present invention is not provided, while the WTGT-P for the inside of the device is at the High (true value) level, the write data of the a-line is erroneously written. Assuming that the shortest data period is 1t, the MFM data has only three periods of 1.5t and 2t. Therefore, a retriggerable monostable circuit operating at the falling edge of the signal a with three time element circuits corresponding to these periods,
The circuits for confirming the period of the write data transmitted next based on 4, 6, and the output thereof are the latch circuits 3, 5, and the gate 7. In the figure, reference numeral 1 denotes a shift register that uses a signal a as a trigger signal and a signal b as data.
That is, when three shift data are monitored by three monostable circuits and three consecutive write data (a signal in FIG. 1) which are not determined to be abnormal are taken into the shift register, a normal write command is issued for the first time. (WT GT-P for internal device) Signal C is output. In FIG. 2, an area A shows the signal state of each element and line when an abnormal interface signal is received due to the occurrence of an erroneous write command, and an area B shows the signal state of each element and line when the normal interface signal is received.

〔The invention's effect〕

According to the present invention, when the device is powered on and the connected higher-level device is powered off, when the erroneous write command is received, the command is logically executed from the cycle of the write data. Since it can be judged as abnormal at the level,
The generation of write command signals for the internal device can be suppressed, and erroneous write operations can be suppressed at the minimum unit level of write data without depending on variations in the characteristics of the mounted magnetic head. Effective for improvement.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of one embodiment of the present invention, and FIG. 2 is a timing chart of the circuit shown in FIG. 1 shift register, 2 retrigable monostable circuit, 3 2-output latch circuit, 4 retrigable monostable circuit, 5 4-output latch circuit, 6 monostable circuit.

Claims (1)

(57) [Claims] 1. A magnetic disk drive used in an interface in which write data is inverted at a constant cycle, a first confirmation circuit for confirming at a theoretical level that the cycle of received write data is within a certain range. A reference time generation circuit for the confirmation circuit; a second confirmation circuit for confirming that the inversion of the write data has continued for a predetermined amount; and a result of the first and second confirmation circuits inside the disk device. A magnetic disk drive provided with a circuit for generating a write command signal to be used.