JPS6151665A - M/t data reading device - Google Patents

Abstract

PURPOSE:To form a sampling clock automatically relative to the recording method of a magnetic tape by controlling the dividing ratio by comparing the phase of a variable dividing output of a reference frequency signal with that of a clock signal written in a magnetic tape. CONSTITUTION:The phase of a reproduction signal of the clock written at the beginning of the magnetic tape, which is read from the magnetic tape by a pulse conversion circuit, and that of the dividing output of the reference frequency signal from an oscillator OSC or variable divider VD are compared in the phase comparing circuit PC. The dividing ratio of the divider VD is determined through a sweep counter SC with reacts to the result to form the sampling clock automatically relative to the recording method of the magnetic tape.

Description

Detailed Description of the Invention [Technical Field] The present invention relates to an M/T (magnetic tape) data reading device, and can be effectively used in an M/T data reading device as an external storage device for a microcomputer, for example. It is related to technology.

[Background technology]

It is known to use audio cassette tapes as auxiliary storage devices for personal computers or microcomputers (for example, from Imohm Co., Ltd. in 1973).
(Refer to page 105 of ``Fundamentals of Microcomputers'' by Mitsuharu Yada, published on April 30, 2003). However, the recording system for cassette tapes is the Kansas City Standard (data can be written/read at 300 baud, the mark (J + logical "1") is 8 cycles of 2400 Hz, and the heath (logical "O") is 1200 Hz ( 7
) 4 cycles), there are various types of 600-bore first class, and they are not unified. Therefore, as a reading device,
Depending on the model, the baud rate is either fixed or switchable. However, even if the above-mentioned switching is possible, it is inconvenient because it is necessary to switch in advance according to the recording method before reading. In addition, even with the fixed type and switchable type, the clock signal for sampling the read data is formed at a fixed oscillation frequency, so if the tape stretches or the tape speed is uneven, the number of readings will decrease. It becomes impossible.

[Purpose of the invention]

An object of the present invention is to automatically form sampling pulses according to the M/T tape recording method.
An object of the present invention is to provide a T data reading device.

The above and other objects and novel features of this invention include:
It will become clear from the description of this specification and the accompanying drawings.

[A essential point of the invention]

A brief overview of typical inventions disclosed in this application is as follows.

That is, the divided output of a variable frequency divider circuit that divides the reference frequency signal formed by the reference oscillator circuit and the clock signal written on the magnetic tape are supplied to a phase comparator circuit, and the output signal of this phase comparator circuit The frequency division ratio of the variable frequency divider circuit is switched to form a sampling signal synchronized with the clock signal.

(Embodiment) FIG. 1 shows a block diagram of an embodiment of a sampling pulse generation circuit in an M/T data reading device.

The signal Din read by the magnetic head is sent to the amplifier A.
It is amplified by rnp and converted into a pulse signal DA by a pulse conversion circuit PL. This pulse signal DA is supplied on the one hand to one input of the phase comparison circuit PC, and on the other hand to a data reading circuit (not shown).

Although not particularly limited, the reference frequency signal generated by the crystal oscillation circuit OSC is frequency-divided by the variable frequency divider circuit VD and supplied to the other input of the phase comparator circuit PC.

This phase comparison circuit PC forms a re-input signal, in other words, a DC signal according to the phase difference (frequency difference) between the pulse signal DA and the frequency-divided output. Although not particularly limited, this phase comparison output is supplied to a sweep counter SC as a control circuit that sets the frequency division ratio of the variable frequency divider circuit VD. This sweep counter performs a counting operation to change the frequency division ratio of the variable frequency divider circuit VD according to the phase comparison output. As a result, the frequency division ratio of the variable frequency divider circuit VD is successively changed.

When the frequency division output matches the phase (frequency) of the pulse signal DA by such a variable frequency division operation, the operation of the sweep counter SC is stopped by the phase comparison output. Therefore, from now on, the variable frequency divider circuit VD repeatedly performs the frequency division operation according to the frequency division ratio at that time.

For such an operation, a clock signal for reading data is written on the magnetic tape at the beginning thereof. That is, as shown in the timing diagram of FIG. 2, the pulse signal DA is such that a certain clock pulse is applied to the leading address portion of the magnetic tape. When the frequency of the initial frequency division output φS of the variable frequency divider circuit VD is high with respect to this clock pulse DA, the sweep counter increases the frequency division ratio by the phase comparison output according to the frequency difference. Perform force 1 Kunt Asobu. As a result, the frequency of the frequency-divided output φS is conversely reduced. Then, the above clock pulse DA and the frequency divided output φ
When the phase matches with S, the sweep counter SC holds this state, and henceforth the variable frequency divider circuit VD forms a pulse signal φS synchronized with the clock pulse DA.

In order to prevent the phase comparison circuit PC or the sweep counter SC from responding to the next read data and changing the divided output φS, for example, the phase comparison circuit PC is stopped from operating. Alternatively, the sweep counter SC is caused to close its input gate.

Thereby, the sampling signal φS synchronized with the clock pulse can be automatically generated. Therefore, by writing clock pulses according to the data recording method, the clock pulses used in the recording method can be automatically reproduced during the read operation.

〔effect〕

(1) Since the clock signal according to the recording method is reproduced to form a sampling signal for reading the written data, a different recording method is automatically selected under the condition that the above clock signal exists. The effect is that data can be read.

(2) Even if there are variations in tape running speed due to tape elongation, differences in tape running speed between different playback devices, or voltage fluctuations in the same playback device, a sampling signal synchronized with the clock pulse is generated accordingly. Therefore, it is possible to obtain the effect that reading errors can be significantly reduced.

(3) According to (1) above, it is possible to obtain the effect that data of different recording methods can be written/read on the same magnetic tape. In other words, if a clock signal according to this recording method is recorded at the beginning of the data,
This is because sampling pulses can be formed in accordance with this.

Although the invention made by the present inventor has been specifically explained based on Examples above, this invention is not limited to the above Examples (although it is understood that various changes can be made without departing from the gist of the invention). Needless to say, for example, there are many types of control circuits that control the frequency division ratio of a variable frequency divider circuit, such as those that convert the comparison output of a phase comparator circuit into a digital signal and supply this as a frequency division control signal. In addition, in order to make it possible to read data of different recording methods from the same magnetic tape, the variable frequency divider circuit and the phase comparator circuit can be controlled by a command to start the read operation. and the control circuit may be brought to the initial state.

[Application field]

The present invention can be widely used in M/T data reading devices in various information processing devices that use magnetic tape as a recording medium.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a timing diagram showing an example of its operation. VD...Variable frequency divider circuit, PC...Phase comparison circuit, Amp
・・Amplification circuit, PL・・Pulse signal conversion circuit, O20・
・Oscillation circuit, SC・・Sweep counter

Claims (1)

[Claims] 1. A variable frequency divider circuit that divides a reference frequency signal formed by a reference oscillation circuit, a phase comparison circuit that receives the frequency division output and a clock signal written on a magnetic tape, and A control circuit that receives an output signal from the phase comparison circuit and switches the frequency division ratio of the variable frequency divider circuit, and forms a sampling signal synchronized with the clock signal from the variable frequency divider circuit. M/T data reading device. 2. The M/T data reading device according to claim 1, wherein the magnetic tape is a cassette tape, and the clock signal is written at the beginning of the magnetic tape.