MEMORY CONTROL SYSTEM

Abstract: There is provided a signal processing system for recording and reproducing a video signal and a digital audio signal with a rotary-head VTR and, more particularly, a memory control system which generates a block address and a memory write signal so that the sync signal for reproduced digital data is detected reliably and the digital data is stored in the memory circuit correctly.

Description: This invention relates to a memory control system used for recording and reproducing serial digital data. Among the techniques of serial digital data recording and reproduction used in extensive fields, a recent application is a digital audio tape recorder (DAT). In a rotary-head digital audio tape recorder (R-DAT), for example, a recording signal is formatted in a constant block period Bt as shown in Fig. 4, in which serial digital data D₀, D₁, ..., D n are preceded by a synchronizing signal (SYNC) with a specific code pattern, a record identification code (ID), a block address code (BA), and an error detection code (EDC) for the ID and BA. Each code is formed of eight bits, and is called "symbol". In the following description, the data of the identification code (ID) indicative of the content of recorded data, etc. is denoted by the symbol W₁, the data of the address code BA is denoted by the symbol W₂, and the data of the error detection code EDC is denoted by the symbol P. The reproducing section has a sync generator providing the same code pattern as that of the recording section, and it compares the reproduced serial digital data with the sync pattern sequentially so as to decide a reproduced signal, when it coincides with the sync pattern, to be a sync signal so that it is used as a reference signal for the successive signal processing. This is the prevalent technique of serial digital data recording and reproduction. The R-DAT employs a modulation system called "8-10 modulation" with its sync signal (SYNC) having a special pattern which does not appear in data normally, so that the accuracy of sync signal detection is appreciably high. However, in a case where a modulation system having a special sync pattern cannot be used by some reason, for example, because of the band limitation of the recording signals such as when recording both an analog video signal and a digital audio signal, it becomes inevitable to use a code pattern contained in data as a sync singal. In this case, false sync signals other than the valid sync signal will appear with high probability, and normal signal processing will be difficult. Although this problem may be solved by increasing the word length of the sync signal (SYNC), it will result disadvantageously in an increased recording frequency or a degraded signal transmission rate. A conventional breakthrough technique for ensuring the sync signal detection without an increased word length of the sync signal is, in addition to the use of a first sync signal detection circuit, to detect predetermined regularity in the contents of two consecutive block address codes BA to utilize it as a second sync signal so that a final sync signal is obtained from a logical product of both the first and second sync signals, as disclosed, for example, in Japanese Patent Unexamined Publication No. 60-137150. The block address code BA generally uses a series of binary numbers increasing continuously from zero, and the detection of a predetermined difference in the value between two consecutive address codes ensures the sync signal detection. However, since the above arrangement utilizes the regularity of two consecutive address codes, it fails to implement the ensured and prompt sync signal detection in such a case where one address code is dropped for example, at the time immediately after the start or the recovery from a code error which has occurred in data reproduction, because it becomes difficult to detect any regularity present in address data values in such a case. Fig. 5 is a block diagram showing a conventional memory control apparatus. In the reproducing operation, serial digital data is inputted through an input terminal 2, and a sync signal detecting circuit 3 detects the sync signal and produces signals which are in phase with the sync signal. The serial digital data is also applied to a block address latch circuit 4, in which the address code BA is latched in response to a latch pulse supplied from the sync signal detecting circuit 3. The serial digital data is further fed to a parity check circuit 5, in which a positive parity check or a negative parity check is made in accordance with the following equation for the code structure shown in Fig. 4, for example. P = W₁ + W₂ or P = W₁ + W₂ where symbol + ○ represents an exclusive-OR operation. The sync signal detecting circuit 3 applies one output thereof to a clock terminal of a block address counter circuit 6, which further receives at its reset terminal rotary head switching pulses (the signal S₁ shown in Fig. 2) indicative of the rotational position of the rotary head (not shown) which are supplied through an input terminal 1. The block address counter circuit 6 has its contents cleared at the edge of a head switching pulse and counts the sync signal until it is cleared by a next head switching pulse. This operation is repeated. In Figs. 1 and 5, numerals indicative of respective short slanting lines crossing the connection lines show bit numbers of digital signals sent through the connection lines, respectively. The block address counter circuit 6 and the block address latch circuit 4 apply their outputs (8 bits) to a block address anticoincidence circuit 8, which decides whether both block address values coincide with each other. The outputs of the block address anticoincidence circuit 8 and the parity check circuit 5 are applied to an AND gate 7, which outputs a pulse when the parity check result is correct and at the same time the block address values do not coincide with each other, and the output pulse is applied to the load terminal L of the block address counter circuit 6, and the 8-bit output of the block address latch circuit 4 is applied to the data terminal D of the block address counter circuit 6 so that the address value of the block address latch circuit 4 is loaded in the block address counter circuit 6. The block address counter circuit 6 produces an 8-bit output, which is outputted through an output terminal 9, and it forms a part of an address signal value for storing the reproduced digital data in a RAM (Random Access Memory). Furthermore, the sync signal detecting circuit 3 and the block address counter circuit 6 supply their outputs to a write signal generating circuit 10, which provides an output through an output terminal 11, and it is used as a write signal for storing the reproduced digital data in the RAM. Hereupon, in a magnetic recording and reproducing apparatus for recording and reproducing a video signal on a magnetic tape by using a rotary head, when recording and reproducing an audio signal in the form of a digital signal, an analog audio signal is digitized at a sampling frequency f s of 48 kHz, for example, so that a frequency ratio of the sampling frequency f s of 48 KHz to the field frequency f v of the video signal of 59.94 Hz in the NTSC system becomes 800.8. The number of data in one field is divided into two kinds, that is, a greater number and a smaller number (e.g., 792 and 810), and supplementary dummy data is added to the field containing a small number of data (792 data in one field) to effect recording. Since the MSB of the address code BA in Fig. 4 is used to record the information indicative of the presence or absence of the supplementary dummy data, the block address value is recorded in 7 bits. For example, when the number of blocks in one field is 135, the lower-order 7 bits of the block address code W₂ include the o-address (0000000) to 127-address (1111111). Then, the next 128-address is indicated by (0000000), and the last 134-address is indicated by 6(=134-128)-address (0000110). The block addresses are recorded in a magnetic tape with these bit indications. However, in digitally recording an audio signal in synchronism with a video signal as mentioned above, the 8-bit block address value for the reproduction cannot be produced directly from the recording block address value, since the recording block address is recorded in 7 bits on the magnetic tape. DE-A-35 39 182 discloses a digital data reproducing system in which address number data which are associated with digital data devided into a number of data blocks are sequentially read out from a recording medium for being used to define the write-in positions of the digital data in a memory. The address number data, which are produced by combining block number data and sub-block number data are compared with predicted address number data which are estimated on the basis of preceeding address number data and, if they are in coincidence or if they are non-coincident only sporadically, they are used for writing-in the reproduced digital data into the corresponding storage positions of the memory. On the other side, if the result of said comparison is that the reproduced address number data and the predicted address number data are non-coincident more than a given number of times, the predicted address number data are used instead of the reproduced address number data for writing-in the reproduced digital data into the storage positions of the memory corresponding to the predicted address number data. According to the present invention, there is provided a memory control system for controlling recording and reproduction of block unit data which includes digital data representing an information signal, a synchronizing signal and an address code indicative of an address value of a block unit in which said digital data is contained, said memory control system comprising: address predicting means which predicts said address code to be read; reading means which reads said address code; address generation means which generates said address value in accordance with said sync signal; composed address value generation means which generates a composed address value on the basis of an output of said reading means and an output of said address generation means; first address value comparison means which compares said composed address value with said predicted address code value; and selection means which outputs said composed address value as an address value instead of said generated address value for accessing a memory circuit only when a comparison error of said first address value comparison means is within a predetermined range; comprising second address value comparison means which compares the address value outputted from said selection means with said predicted address code value; and writing signal generation means which generates a writing signal for storing said digital data in said memory circuit only when a comparison error of said second address value comparison means is within a predetermined range. According to one aspect of the invention, said block unit data is recorded at a predetermined position on a track of a magnetic tape, and wherein said address predicting means predicts said address code to be read in accordance with a rotational position of a rotary head which reproduces data recorded on said magnetic tape. The memory control system comprises a block address predicting means which predicts an address recorded at a reproducing position in accordance with the rotational position of a rotary head, a composed address generating means which produces a composed address value from a reproduced address value read out from a magnetic tape by the rotary head and an output address value, a first address value comparing means which compares the composed address value with the predicted address value provided by the block address predicting means, an address selecting means which selects the composed address value as a new output address value only when a comparison error provided by the first address value comparing means is within a predetermined range, a second address value comparing means which compares the output address value from the address selecting means with the predicted address, and a write signal generating means which produces a write signal for storing in a memory the reproduced digital data reproduced from the magnetic tape only when a comparison error provided by the second address value comparing means is within a predetermined range. In the reproduction from a magnetic tape on which a digital signal having a sync signal and an address added thereto is recorded with a rotary head so that the sync signal and the address are located at a predetermined position on the track, the rotational position of the reproducing rotary head is detected to predict the recorded address (8 bits), a composed address value (8 bits) is produced from the reproduced address value (7 bits) and the output address value (the most significant 1 bit among the 8 bits), the composed address value (8 bits) is compared with the predicted address value (8 bits), and the composed address value is adopted as a new address value when a comparison error is within a predetermined range, whereby a correct address value is produced. In addition, the output address value is compared with the predicted address value, and a write signal for storing the reproduced digital data in the RAM is generated only when a comparison error is within a predetermined range, whereby the digital data can be written only at a location close to a correct address. As described above, a most significant bit of the block address value is obtained while limiting a range of the block address value by using an address value predicted from the rotational position of the rotary head, whereby the reproduced digital data can be stored in the RAM with a correct block address value. Further, in the case of a failure of parity check whereby a correction of the block address value has been made erroneously, the write signal is generated in a region in the block address value range which has been limited by the predicted address value, and the range of RAM area, in which the reproduced digital data is stored, is confined to be close to the predicted address value. As a result, even if a complete track of reproduced digital data is not stored in the RAM, it is possible to initiate an error correction process for the reproduced digital data stored in the RAM, so that it is made possible to make a significant reduction in time after the reproduced digital data has been stored in the RAM and before the error correction process is started. Therefore, a data processing time at the time of reproducing a digitally recorded audio signal is reduced significantly, and hence a processing delay time difference (T D ) of an audio signal from a video signal at the time of recording and reproducing both signals can be minimized. Especially, even when the number of times (n) of dubbing is increased, since the processing delay time difference in this case (T Dn = T D x n) of an audio signal from a video signal is still small, a magnetic recording and reproducing apparatus having a unnoticeable processing delay time difference can be realized. Fig. 1 is a block diagram showing the memory control system of this invention; Fig. 2 is a waveform diagram showing the main signal waveforms in the memory control system shown in Fig. 1; Fig. 3 is a signal structure diagram showing the format of serial digital data to be supplied to the input terminal 2 in Fig. 1; and Fig 4 is a block diagram showing a conventional memory control system. Fig. 1 is a block diagram showing the memory control system embodying the present invention, and Fig. 2 is a waveform diagram showing the signals appearing at various portions in Fig. 1. In the reproducing operation, an input terminal 2 in Fig. 1 receives serial digital data, and a sync signal detecting circuit 3 detects the sync signal and produces a signal which are in phase with the sync signal. A block address latch circuit 4 extracts and latches an address code BA in the serial digital data in response to the latch pulse supplied from the sync signal detecting circuit 3. A parity check circuit 5 implements an even-parity test or an odd-parity test for the serial digital data in accordance with the following equation for the code structure shown in Fig. 4, for example, in response to a pulse supplied from the sync signal detecting circuit 3. p = W₁ + W₂ or W₁ + W₂ where symbol + ○ denotes an exclusive-OR operation. The output of the sync signal detecting circuit 3 is applied to a clock input terminal of a block address counter circuit 6, and a head switching pulse signal (shown by S₁ in Fig. 2) indicative of a rotational position of the rotary head (not shown) is supplied through an input terminal 1 and is applied to a reset terminal of the block address counter circuit 6. The count value of the block address counter circuit 6 is shown by signal S₂ in Fig. 2. The block address counter circuit 6 is reset by the head switching pulse, and then it restarts to count up the sync signal using it as a clock signal until it reaches the maximum block address value (134) and stops there. Then, the counter is reset by a next head switching pulse signal, and these operations are repeated. The block address counter circuit 6 and the block address latch circuit 4 apply their lower-order 7-bit outputs to a block address anticoincidence circuit 8, which tests whether both block address values are equal to each other. The lower-order 7-bit output from the block address latch circuit 4 and the most significant 1-bit output from the block address counter 6 are applied to a composed block address generating circuit 21, which produces a composed block address value, with the most significant bit being supplied from the output of the block address counter circuit 6 and with the lower-order 7 bits being supplied from the output of the block address latch circuit 4. A reference block address generating circuit or a predicted address generating circuit 22, which is formed of a counter circuit, receives at its reset terminal a head switching pulse signal supplied from the input terminal 1, and it operates to count up an internal reference clock. The content of the counter is shown analogously by signal S₃ in Fig. 2. The circuit 22 is reset by the head switching pulse signal, and then it restarts to count up the internal reference clock until it reaches the maximum block address value (134) and stops there. These operations are repeated, and block address values corresponding to the head position are generated. The reference block address generating circuit 22 and the composed block address generating circuit 21 apply their 8-bit outputs to a first address value comparing circuit 23. The first address value comparing circuit 23 conducts the following computation of an absolute value. N₁ = |N A - N B | where N A denotes a predicted address value provided by the reference block address generating circuit 22 and N B denotes a composed address value provided by the composed block address generating circuit 21. The circuit 23 further compares the computation result N₁ with a predetermined value The parity check circuit 5, the block address anticoincidence circuit 8 and the first address value comparing circuit 23 apply their outputs to an AND gate circuit 7, which produces an output pulse on condition that the parity test result is correct, the block address values do not coincide with each other, and besides the following condition is met. (The signal S₄ in Fig. 2 shows a range which satisfies this condition. The broken line shows the signal S₃, and the parallelogram shown by the solid line and including the broken line as its center line represents the above-mentioned range.) The output pulse of the AND gate circuit 7 is applied to a load terminal L of the block address counter circuit 6. The composed block address generating circuit 21 has its 8-bit output applied to a data input terminal D and loaded in the block address counter circuit 6 in response to the load pulse supplied from the AND gate circuit 7. The 8-bit output of the block address counter circuit 6 is sent out through an output terminal 9 to form a part of an address value for storing the reproduced digital data in the RAM. The sync signal detecting circuit 3 and the block address counter circuit 6 apply their outputs to a write signal generating circuit 10, and the block address counter circuit 6 and the reference block address generating circuit 22 apply their 8-bit outputs to a second address value comparing circuit 24. The second address value comparing circuit 24 conducts the following computation of an absolute value. N₂ = |N A - N C | where N A denotes a predicted address value provided by the reference block address generating circuit 22, and N C denotes an output address value from the block address counter circuit 6. Further, the second address value comparing circuit 24 compares the computation result N₂ with a predetermined value Next, the write signal generating circuit 10 and the second address value comparing circuit 24 apply their outputs to an AND gate circuit 25, which produces a write signal when the following condition is met. (This condition is represented by the internal area of the parallelogram of the signal S₄ shown in Fig. 2 by the solid line and including the broken line as its center line.) The write signal is sent out through an output terminal 11, and it is used as a write signal for storing the reproduced digital data in the RAM. Although, in this embodiment, the error detection code, etc. have a 8-bit code length, any optional value may be used to meet the requirement of the system specifications.

Claims: A memory control system for controlling recording and reproduction of block unit data which includes digital data (D n ) representing an information signal, a synchronizing signal (SYNC) and an address code (W₂) indicative of an address value of a block unit in which said digital data (D n ) is contained, said memory control system comprising: address predicting means (22) which predicts said address code (W₂) to be read; reading means (4) which reads said address code (W₂); address generation means (3,6) which generates said address value (W₂) in accordance with said sync signal; composed address value generation means (21) which generates a composed address value on the basis of an output of said reading means (4) and an output of said address generation means (3,6); first address value comparison means (23) which compares said composed address value with said predicted address code value; and selection means (6,7) which outputs said composed address value as an address value instead of said generated address value for accessing a memory circuit only when a comparison error of said first address value comparison means (23) is within a predetermined range; characterized by second address value comparison means (24) which compares the address value outputted from said selection means (6,7) with said predicted address code value; and writing signal generation means (10,25) which generates a writing signal for storing said digital data (D n ) in said memory circuit only when a comparison error of said second address value comparison means (24) is within a predetermined range. A memory control system according to claim 1, wherein said block unit data is recorded at a predetermined position on a track of a magnetic tape, and wherein said address predicting means (22) predicts said address code (W₂) to be read in accordance with a rotational position of a rotary head which reproduces data recorded on said magnetic tape.

Inventors: ISHIWATA, TETSUO, KOMAE, HITOSHI, TANAKA, HIROSHI, YAMAGUCHI, SUSUMU, YAMAUCHI, EIJI, YOSHINO, TADASHI
Applicants: MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1988
Main classification: G11B20
IPC codes: G11B27, G11B20, H04N9, H04N5