Synchronization Scheme for a Digital Recording System
Abstract Generated abstract
This paper examines synchronization circuits for forming pulse sequences used to mark magnetic tape in a digital recording system, where asynchronous start signals can distort the first or last pulses of a recorded series. It compares two existing schemes, one using two shifted synchronization-pulse sequences and another using a single sequence, and analyzes how they can be adapted with a counter feedback loop and start-stop control. The authors argue that the single-sequence scheme is simpler, requires less equipment, permits straightforward inhibition of pulse generation for specified intervals, and provides a more practical basis for a synchronization unit than the two-sequence alternative.
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SYNCHRONIZATION SCHEME FOR A DIGITAL RECORDING SYSTEM
A. V. TRIKHANOV, P. P. GRIGOR'EV, A. N. OSOKIN
(Presented by the scientific seminar of the Department of Computer Engineering)
The synchronization scheme is intended to ensure the recording of series of synchronization pulses without distortion of the pulses at the beginning and end of the series. The start of recording of the series is determined by the “start” signal, which may arrive at an arbitrary moment in time. Without a synchronization scheme, the initial pulses of each series may be distorted, and, during playback of the recorded series of synchronization pulses, this may lead to unreliable operation of certain circuits in which series of synchronization pulses are used. Synchronization issues are discussed in [1, 4]. The scheme described in [4] is used to select one pulse from a series according to the “start” signal. For this purpose two pulse sequences are required, one of which is shifted relative to the other by half a period. The scheme is rather complex (Fig. 1) and, for implementation, requires five two-input coincidence circuits, two flip-flops, one three-input coincidence circuit, and a collecting circuit with two inputs. The operating diagrams of the scheme are given in Fig. 2. In [1] a scheme is presented for selecting one pulse when one series of synchronization pulses is present. This scheme (Figs. 3, 4) is simpler.
Fig. 1. Synchronization scheme with two series of synchronization pulses
Fig. 2. Operating diagrams of the synchronization scheme with two series of synchronization pulses
Both of these schemes may be used for constructing a unit for forming the sequence of synchronization pulses needed for marking magnetic tape in a digital recording system [2], in accordance with the “start” and “stop” signals. Let us consider in more detail the use—
use of the circuit from [1]. This possibility is associated with including in the feedback loop of a counter with a conversion factor equal to the number of pulses in the sequence. The signal from the output of the most significant digit of the counter can be used in different ways: either to stop the operation of the circuit and, after a specified delay, start the circuit again, or to prohibit the generation of sequence pulses for a specified time. As the comparison shows, the second variant requires less equipment.
Fig. 3. Synchronization circuit with one series of synchronizing pulses
Fig. 4. Operating diagrams of the synchronization circuit with one series of synchronizing pulses
When the operation of the unit is stopped by a signal from the control panel, the sequence of pulses must be formed completely; for this purpose one can use the inhibition of the next start of the unit, for example as implemented in the Minsk-1 digital computer [3]. In this case the operation of the unit after each sequence must cease.
In the case when, at the end of the sequence, inhibition of pulse generation follows, the signal from the most significant digit should be used to terminate the operation of the unit. This stopping variant is more preferable in comparison with the first, since it requires a lower operating frequency of the start flip-flop. Figures 5 and 6 show the functional circuit and timing diagrams of the operation of the unit with allowance for the inhibition of the generation of synchronizing pulses. The one-shots \(OB_2\) and \(OB_3\) determine different intervals of inhibition of the generation of synchronizing pulses [2].
It turns out that the circuit from [4] offers fewer possibilities for constructing a synchronization-pulse-sequence generation unit.
Fig. 5. Synchronization unit with one series of synchronization pulses
Fig. 6. Operating diagrams of the block diagram of synchronization with one series of synchronization pulses
pulses. It does not allow the prohibition of synchronization-pulse generation to be introduced in such a simple explicit form as was done in the circuit
from [1]. In addition, the synchronization unit constructed on the basis of this scheme is more complex than the synchronization unit constructed on the basis of the scheme from [1], and requires two series of synchronization pulses for operation.
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V. P. Petrov. Design of Digital Control and Management Systems. Moscow, Mashgiz, 1967.
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A. V. Trikhanov et al. Marking of magnetic tape in a digital recording system. In the present collection.
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Universal Digital Computer “Minsk-1.” Technical Description. Minsk, 1962.
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Universal Digital Computer “Ural-11B.” Technical Description. Penza, 1967.