JPS58169306A - Video tape reproducing device of pulse code modulating system - Google Patents

Abstract

PURPOSE:To keep a recording quality of a video tape satisfactorily, by counting the number of times of outpus of an error detecting signal of a data block, and dislaying a warning when its value reaches a specified counting value, when digital-dubbing a video reproducing signal. CONSTITUTION:For instance, an allowable value of an error of a data which is read out from a tape in 15sec is set. An error data pulse is inputted to a 4-bit ripple counter 12 and 14 through a data error detecting circuit 1 and an edge generating circuit 2, and is counted. Both outputs of the counters 12 and 14 are cleared in case when the number of detecting signals counted in 15sec does not exceed the allowable value, and counting is started again. When the counting value of 15sec reaches the allowable value, a display signal is outputted from an AND circuit 15, an LED 21 emits light, and it is displayed that deterioration of recording exceeds the allowable value. In this way, an error of digital dubbing can be corrected at a specified time, therefore, a recording quality of a video tape can be kept satisfactorily.

Description

Detailed Description of the Invention The present invention provides a decoding system that outputs a detection signal when a data error is detected in the digital signal while decoding a digital signal reproduced from a videotape into an analog signal. The present invention relates to a pulse code modulation type video tape playback device equipped with a circuit.

Conventionally, pulse code modulation video tape playback devices
For the decoding circuit, the pulse code modulation signal arrangement for consumer pulse code modulation encoding and decoding specified by the Japan Electronics Industry Association (the signal arrangement of the first field is shown in Figure 1 (
1k), the signal arrangement of the second field is as shown in Fig. 1 (however, the unit H is one horizontal scanning period), and the signal arrangement in bit units of the horizontal signal is as shown in Fig. 2). In addition to decoding the reproduced digital signal into an analog signal, it also outputs a detection signal when a data error is detected in the digital signal and activates a warning means, indicating that the videotape recording has deteriorated. Display the fact that the To explain this more specifically, if there is a data error in one data block, the next bit of the error detection word (CRC) of that data block, that is, the bit indicated by the symbol T in FIG. At the same time as the detection signal is read out, the detection signal changes from 10'' to 111, and after that state continues for one horizontal scanning period (168 bits), it returns to 0@.In other words, in Fig. 3(a), the detection signal of B changes. If there is an error in the data block, at the same time as reading the next bit of the error detection word (CRC) of the data block B,
The detection signal changes from 101 to 111, and at the same time as reading the next bit of the error detection word (CRC) of data block C, the detection signal returns from 111 to Sol (
(see Figure 3(b)). Therefore, the person handling the videotape should judge the degree of deterioration of the videotape recording while looking at the warning display, and take steps to correct the videotape recording before it becomes impossible to correct the error. Record it again on another videotape. By the way, since the level of confirmation of warning displays and the criteria for determining the degree of deterioration differ depending on the person handling the videotape, sometimes it becomes impossible to correct errors, and the recording of the digitally dubbed videotape is deteriorated from the beginning. There was a drawback that made it possible.

In order to eliminate the drawbacks of the conventional example, the present invention provides a video tape that counts the frequency of warning indications at a certain period, and when the frequency exceeds a certain value, displays that the recording of the video tape has deteriorated. The present invention provides a pulse code modulation type video tape playback device that is equipped with a deterioration warning circuit. Examples of the present invention will be described in detail below.

FIG. 4 shows the configuration of an embodiment of the present invention. Reference numeral 1 denotes a data error detection circuit incorporated in a pulse code modulation decoding circuit (not shown). If there is a data error in the data block decoded by the modulation/decoding circuit, a detection signal is output. 2 is, for example, an LS, which is set by an inverter 3, a NOR circuit 4, a capacitor 5, and a resistor 6 so that the pulse width of the output pulse is 0.5H.
123 monostable multivibrator 7, a monostable multivibrator 10 such as LS 123, which is set by a capacitor 8 and a resistor 9 so that the pulse width of the output pulse is 0.55 H, and an AND circuit 11. In the edge generation circuit 2 configured as shown in FIG. 5, the data error detection circuit 1 continuously outputs n detection signals, and one detection signal with a pulse width of nH is input. Even if n pulse signals are output. 12 is a BN 7416104 bit triple counter, for example, whose CLOCR terminal is connected to the output terminal of the edge generation circuit 2;
13 is RTPPLEC of 4-bit triple counter 12
An inverter whose input terminal is connected to the ARRY terminal, 14 is a BN 7416104 bit triple counter whose CLOCK terminal is connected to the output terminal of the inverter 13, and 15 is a 4-bit triple counter Q of 12 and 14.
16 is an AND circuit with six input terminals connected to the A terminal, Qc terminal, and QD terminal, respectively, and two NOR circuits 17
and 18, one input terminal of the gate circuit 16 is connected to the output terminal of the AND circuit 15, and the other input terminal of the gate circuit 16 is connected to the reset switch 19. When the AND circuit 15 outputs a display signal when the reset switch 19 is in a conductive state, the gate circuit 16 outputs a signal. 20 is a switching transistor whose base is connected to the output terminal of the gate circuit 16, 21 is a light emitting diode that is blinked by the switching transistor 20, 22 is an oscillator with an oscillation frequency of IHz, and 23 is a Schmitt trigger that shapes the waveform of the output signal of the oscillator 22. The circuit 24 is a 4-bit triple counter, for example, 8N 74161, whose CLOCK terminal is connected to the output terminal of the Schmitt trigger circuit 23, and 25 is the R circuit of the 4-bit triple counter 24.
This inverter has an input terminal connected to the IPPLE CARRY terminal, and an output terminal connected to the CIJAR terminals of the 4-bit triple counters 12 and 14, respectively.

In this embodiment configured in this way, for example, 15
If the error rate of data read from videotape per second is set to 10-3, 60 fields are read per second, and 245 data blocks are read per field, so the total number of data blocks read in 15 seconds is: , 245 x 60 x 15 = 220.500
Tonari, TV number o to -3ha, 220.5 and naru.

Therefore, the 4-bit triple counters 12 and 14 are 22
In order to output a display signal from the AND circuit 15 when one detection signal is counted, the QA of the 4-bit triple counter 12 corresponding to the 2° digit, 22nd digit, and 23rd digit, respectively.
terminal, QC terminal, to terminal wo, and 4 pins corresponding to 24 digits, 2 digits, and 2 digits respectively) Connect the QA terminal, QC terminal, and QD terminal of the IJ pull counter 14 to the AND circuit 15. In addition, 1 is applied to the 4-bit triple counters 12 and 14.
A 4-bit triple counter 24 is connected between the oscillator 22 and the 4-bit triple counters 12 and 14 in order to repeatedly perform a counting operation for 5 seconds and a clearing operation for 1 second. Then, 4 bit ripple 1. The number of detection signals counted by counters 12 and 14 in 15 seconds is 2.
20 or less, the outputs of the 4-bit triple counters 12 and 14 do not become (1101), so the 4-bit triple counters 12 and 14 are cleared before the AND circuit 15 outputs the display signal, and again, Counting is done again. However, 4-bit triple counter 1
The number of detection signals counted by 2 and 14 in 15 seconds is 221.
When , the outputs of the 4-bit triple counters 12 and 14 become (1101), and the signals output from the QA, QC, and QD terminals of the 4-bit triple counters 12 and 14 all become 111. , AND circuit 15
A display signal is output from the light emitting diode 21, and the light emitting diode 21 emits light to indicate that the deterioration of the videotape recording has exceeded the permissible range, that is, the data error rate of 10.

As explained above, according to the present invention, the number of output detection signals is counted by a counter and a warning is displayed when a certain count value is reached. This has the advantage that the recording quality of the videotape can be maintained at a good level since it can be done at a certain time.

[Brief explanation of the drawing]

FIG. 1(a) is a diagram showing the signal arrangement of the first field, FIG. 1(b) is a diagram showing the signal arrangement of the second field,
3 is a diagram showing the bit-by-bit signal arrangement of the horizontal signal, FIG. 3 is a diagram showing the output timing of the detection signal, FIG. 4 is a circuit diagram of an embodiment of the present invention, and FIG. 5 is a diagram showing the output timing of the detection signal. FIG. 2 is a circuit diagram of an edge generation circuit according to an embodiment. l...Data error detection circuit, 2...
Curved edge generation circuit, 12.14.24...-
... 4-bit triple counter, 13.25...
・・・・・・Inverter, 15・・・・・・AND
Circuit, 16...Gate circuit, 19...
- Open - Reset switch, 20... - Switching transistor, 21 - Song... Light emitting diode, 22... Song - Oscillator, 23...
...Schmitt trigger circuit.

Claims (1)

[Claims] A pulse code modulation system is equipped with a decoding circuit that outputs a detection signal when a data error is detected in the digital signal while decoding a digital signal reproduced from a videotape into an analog signal. In the videotape playback device, a counter counts the number of the detection signals, a clearing means outputs a clear signal at a constant cycle to periodically clear the counter, and the counter counts the number of the detection signals. display control means for outputting a display signal and activating the display means when a predetermined number is counted during the predetermined period; A videotape deterioration warning circuit is provided which activates the front thread means to warn that the deterioration of the recording of the videotape has exceeded a permissible range when the number exceeds the predetermined number. A videotape playback device using pulse code modulation.