JPS58224418A - Circuit for reading tape - Google Patents

Abstract

PURPOSE:To reproduce stably digital data, by combining an amplifier to which an output signal from a magnetic tape is inputted, the 1st FF and the 1st and 2nd monostable multivibtators which are to be driven successively by an output from the amplifier, a differential circuit, and a latch circuit. CONSTITUTION:The amplifier 2 amplifies a reproduced waveform 1 from a tape and converts the analog signal into a digital one. In synchronization with the output 3 of the amplifier 2, an FF 4 is driven and the monostable multivibrator 7 is driven in accordance with the level change of the output 5. In synchronization with the output 8, the 2nd monostable multivibrator 9 is driven. The output of the monostable multivibrator 9 is inputted to the differential circuit 11 to form a synchronous signal 12. An FF 6 latches the output of an FF 5 synchronously with the output 10 of the monostable multivibrator 9. After completion of the latching, the output of the FF 4 is set up by the output pulse 12 of the differential circuit 11. By said sequence, the output of the FF 6 is made correspond to V level in case of ''0'' data and ''0'' level in case of ''1'' data, so that the reliability can be sharply improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tape reading circuit capable of stably reproducing digital data recorded using the FSX method.

Page 2 Recent advances in semiconductor technology have led to the development of LSi chips (devices) with a wide range of intelligence functions. Among these, the so-called μm processors have become easier and cheaper to obtain with functions that surpass those of the minicomputers of the past. Computers have arrived. However, as the central part of computers has become more integrated and available at lower prices, the input/output devices have become more important in the system. In particular, as computers have recently become available for tens of thousands of yen, there has been a demand for display devices or external storage devices commensurate with the price. In order to meet these demands, a method has been proposed that uses existing input/output devices, such as a home television receiver as a display device and an audio cassette magnetic tape device as an external storage device.

Manchester coding method and FSK method are methods for recording 3-page digital data using an audio cassette magnetic tape device.

Various methods such as baseband method and FM method have been proposed, but the simplicity of the circuit configuration is important.

In consideration of data reliability, the FSK method has recently become mainstream. Also in the FSK method, Fig. 1 a -
As shown in a, there are cases where the times at which Pa○'' and '1'' are shown are different, and there are cases where the number of repetitions is different, but basically, the pulse trains with periods T and 2T are used to show '0' and '1'. 1
1111 can be expressed.

When recording and reproducing digital data with an audio magnetic tape device, particular problems arise in the signal input circuit of the audio magnetic tape device, uneven rotation of the motor, and frequency characteristics of the internal circuit. Normally, the signal input circuit of an audio magnetic tape device is a differentiating circuit as shown in FIG. 2, which has a relatively large time constant, and the frequency characteristics (fc = 5 to 5) of this and an internal circuit (not shown) are used. 7KH
Because of 2), the harmonic components of the rectangular pulse signal are removed, and both the rising edge and the falling edge become sharp, and the signal becomes approximately like a distorted Sign wa vθ. Furthermore, since the charging/discharging state of the differentiating circuit is slightly different, the pulse d of the signal during reproduction is usually different from that during writing. FIGS. 3a, b, and c respectively show write data and reproduced waveform 2 according to the FSK method and their waveforms after shaping.

Another reason for the difference in the signal pulse l during reproduction is the waveform shaping circuit of the reproduced signal. The waveform reproduced from an audio magnetic tape usually has a waveform as shown in FIG. Waveform shaping circuits are often composed of amplifiers and Schmitt circuits with high gain.
h level), the state is reversed. This threshold level differs somewhat depending on the circuit to be constructed, but in principle it cannot be set to 0 level, so as shown in FIG. 3C, there is a fluctuation in the pulse width of T+(τT2>T).

However, considering the data cycle, it is almost constant, and TN-T
2=2T, and Ts=T4=T.

Page 5 In view of the following two points, it is an object of the present invention to provide a tape reading circuit capable of solving the above-mentioned problems and outputting a stable reproduction signal.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 is a block diagram showing the configuration of a tape reading circuit according to an embodiment of the present invention, and FIGS. 5a to 5g are timing charts for explaining its operation.

A reproduced waveform 1 (FIG. 6a) from an audio magnetic tape device (not shown) is input to an amplifier 2 having a fixed threshold level.

゛ This amplifier approximately converts an analog quantity into a digital quantity by amplifying the data from the audio magnetic tape device with a gain G (FIG. 6b). In other words, below the threshold level of the amplifier is “O”.
The output is amplified beyond that until the output becomes "1". The amplified output 3 is input to the first flip-flop circuit 4. The flip-flop circuit 4 is driven in synchronization with the rise of the output 3 of the amplifier 2. Assuming that the output 6 2j 5 of the flip-flop circuit 4 (FIG. 6C) is initially at LOW level,
Changes to Hj4h level. flip-flop circuit 4
The monomulti circuit 7 (pulse width=t1) is driven in synchronization with the change of the output from LOW level to HIGH level. tl is a time related to 1-bit data length, and must satisfy α×1-bit data length≦t1<1-bit data length. Here, α needs to be set to a time that can ignore fluctuations in the Luhals width due to the Unaslenoshhold level as described above, and experimental results have shown that if it is % or more, it can be used sufficiently without malfunction. .

Although the upper limit is still set at 1 bit data length, it is more appropriate to set the data length to about 0.9×1 bit data length in consideration of rotational unevenness and the like. Output 8 of still mono multi circuit 7 (Fig. 6 d)
The second mono multi-circuit 9 is driven in synchronization with the falling of the angle. If the pulse width of the monomulti circuit 9 is t2, then t1]-t2(1 bit data length must be satisfied.Next, the output of the monomulticircuit 9 is input to the differentiating circuit 11, and the monomulticircuit 9
A pulse 12 (FIG. 6f) is generated in synchronization with the falling edge of the output. The flip-flop circuit 6 is only for latching the output 6 of the flip-flop circuit 4, and is latched in synchronization with the rise of the output 10 (FIG. 5e) of the monomulti circuit 9. , after t2 after completion of this operation, the output of the flip-flop 4 is set by the output pulse 12 (FIG. 6f) of the differentiating circuit 11. With this sequence, the output 13 of the flip-flop circuit 6 (Fig. 6g) is
t1 time after the rise of the output 3 of the multiplier 2, “b
When the data is ``'', the output corresponds to the V level. When the data is 1111+, the output corresponding to the O level is obtained.

The output 13 of the flip-flop circuit 6 reproduced in this way
The pulse width t4. t4' is equal to each data cycle to, to' of the reproduced waveform, and since each data cycle is almost constant, t4' is t4', and the timing at which this output 13 is read is determined by fluctuations in the output signal. However, it is still possible to read with good reproducibility even if the playback level and sound quality adjustment range of the audio output magnetic tape device are changed to some extent.

FIG. 6 is a circuit diagram showing the detailed configuration of the embodiment shown in FIG. 4, in which a D-type flip-flop circuit is used as the flip-flop circuit.

As explained above, the present invention includes an amplifier to which an output signal from an audio magnetic tape device is input, a first flip-flop circuit driven by the output of the amplifier,
a first mono multi circuit that operates in synchronization with the output of the first flip-flop circuit; a second mono multi circuit driven by the trailing edge of the output of the first mono multi circuit; and a second flip-flop circuit which latches the output of the first flip-flop using the output of the differentiating circuit which receives the output of the mono multi-circuit. The reliability when used as a device can be greatly improved.

9 pages

[Brief explanation of the drawing]

Figures 1 a - c are diagrams for explaining the FSK method, Figure 2
3 is a signal input circuit diagram of a general audio magnetic tape device, FIGS. 3a to 3c are diagrams for explaining pulse width fluctuations of reproduction signals of an audio cassette magnetic tape device, and FIG. 4 is a diagram of a tape according to the present invention. A circuit diagram showing an embodiment of the reading circuit, FIGS. 6a to 6g are timing charts for explaining the operation of the embodiment, and FIG. 6 is a detailed circuit diagram of the embodiment. 2...Amplifier, 4,6...Flip-flop circuit, 7,9...Mono multi circuit, 11
・・・・・・−Differential circuit. Patent applicant Makoto Ishizaka, Director of the Agency of Industrial Science and Technology - Figure 1 Figure 2 J Ward 9;

Claims (1)

[Claims] an amplifier to which an output signal from an audio magnetic tape device is input; a first flip-flop circuit driven by the output of the amplifier; and a first flip-flop circuit that operates in synchronization with the output of the first flip-flop circuit. a second mono multi circuit driven by the trailing edge of the output of the first mono multi circuit, and an output of a differentiating circuit into which the output of the second mono multi circuit is input. and a second flip-flop circuit for latching the output of the first flip-flop circuit, the tape reading circuit reproducing digital data recorded by the FSK method.