PROCEEDINGS
OF THE TOMSK POLYTECHNIC INSTITUTE
NAMED AFTER S. M. KIROV

Vol. 266　　　　　　　　　　　　　　　　　　　　　　　　　1976

MARKING OF MAGNETIC TAPE

IN A DIGITAL RECORDING SYSTEM

A. V. TRIKHANOV, A. N. OSOKIN, P. P. GRIGOR’EV

(Presented by the scientific seminar of the Department of Computer Engineering)

At the Department of Computer Engineering of TPI, a system has been developed for digital recording and input into an electronic digital computer of continuous electrical signals. The recording of digital codes is carried out on a pre-marked magnetic tape (MT). In turn, the marking of the MT consists of recording synchronizing pulses (SP) on a special track.

Fig. 1. Variants of information placement on magnetic tape

The synchronizing pulse is recorded opposite each line of code information and each pulse of the zone number \((N_{\text{zn}})\). The sequence of synchronizing pulses recorded on the MT is determined by the method of placing code information on it. Figure 1 shows three methods of such placement when recording in:

1) the magnetic-tape storage unit of an electronic digital computer,

2) a digital recording system with continuous motion of the MT to its end (system 1),

3) a digital recording system with overlap in time between recording in a given zone and searching for the next zone (system II). In Fig. 1 the following notation is used:

\(T_{\text{zn}}\) — time for recording the zone number,

\(T_{\text{op max}}\) — maximum release time of relay P,

\(T_{\text{vr min}},\ T_{\text{vr max}}\) — minimum and maximum operate time of relay P,

\(T_{\text{st}},\ T_{\text{start}}\) — stopping and starting time of the tape-transport mechanism (LPM).

Relay P is used to connect the magnetic-head unit either to the outputs of the recording amplifiers or to the inputs of the playback amplifiers.

When recording on magnetic tape, the total time interval between the codes of adjacent zones is determined for the indicated placement methods as follows:

1) \(T \geq T_{\text{st}} + T_{\text{start}} + T_{\text{zn}} + T_{\text{vr max}},\)
2) \(T \geq T_{\text{op max}} + T_{\text{zn}} + T_{\text{vr max}},\)
3) \(T \geq T_{\text{vr max}} - T_{\text{vr min}}.\)

For the RS3 relay and the LPM of the “M-220 M” machine [1]:

1) \(T \geq 70\ \text{ms},\)
2) \(T \geq 40\ \text{ms},\)
3) \(T \geq 10\ \text{ms}.\)

In the last two cases, when reading in the NLM of the machine, after reproducing each zone the tape should be returned backward by several zones.

When marking magnetic tape, it becomes necessary, in order to create zones of a definite length, to use counters. Thus, for example, in the autonomous mode of the M-220 M storage unit, a counter of the number of numbers is used. To mark a zone of a definite length, determined by the number of words that can be recorded in it, a definite number is set on the control panel of the M-220 M storage unit (32, 64... 2048, 4096). Depending on the number set, the capacity of the zone will be determined. Since words consist of six rows, one word-count counter is sufficient; the three low-order bits are used as a row-count counter. When using storage units for recording at different frequencies, two counters are required: a counter that determines the capacity of the code-material zone, and a counter that determines the length of the zone number. When recording and marking at one frequency, the second counter can be dispensed with, since the length of the zone number is a small value for M-220 machines (12 bits with markers), i.e., the indicated counter can be replaced by a one-shot multivibrator.

Fig. 2. Marking circuit

With variable frequency the latter is inadmissible, since the duration of the zone number is different. However, it is also possible to get by with a single counter that combines the functions of both counters. This is implemented in the digital recording system [2]. The marking circuit, which includes the counter, is shown in Fig. 2; timing diagrams of the operation of the circuit in system 1 mode (the operating mode is set by switch P) are shown in Fig. 3. The main part of the circuit is the line-number counter, since in this system eight-bit numbers are written on the magnetic tape. The number of lines coincides with the number of words. The four low-order bits constitute the counter of the number of synchronization pulses in the zone number. Before the start of operation register $\mathrm{R}_{\mathrm{g}2}$ is in the zero state, and the code for the number four is written in $\mathrm{C}_{\mathrm{g}}$.

Fig. 3. Timing diagrams of operation of the marking circuit

After the circuit is started, $\mathrm{C}_{\mathrm{ch}}$ begins to count synchronization pulses $\mathrm{SI}$ from the output of the pulse generator. After the 12th pulse has been counted, the 5th bit of the counter is set to the one state, and the circuit $\mathrm{Sp}_4$ opens. A signal from its output starts $\mathrm{Ov}_2$ and sets $\mathrm{R}_{\mathrm{g}2}$ to the one state. A signal from this register opens $\mathrm{Sp}_3$, through which, from the output of $\mathrm{Sb}_1$, a signal passes to set $\mathrm{C}_{\mathrm{ch}}$ to the zero state. After a certain delay (120 $\mu$sec), determined by the duration of the pulse from $\mathrm{Ov}_2$, $\mathrm{C}_{\mathrm{ch}}$ begins to count pulses, the count continuing until the number 24576 is registered; after this $\mathrm{Ov}_2$ operates, which enters the code of the number four into $\mathrm{C}_{\mathrm{ch}}$ and sets $\mathrm{R}_{\mathrm{g}2}$ to the zero state. After the delay, $\mathrm{C}_{\mathrm{ch}}$ again begins counting pulses with a conversion factor equal to 12. Thus the operation of the circuit will repeat. In system II mode, after 24576 lines the one-shot $\mathrm{Ov}_1$ operates for 10 $\mu$sec (see Fig. 1).

REFERENCES

1. E. A. Drozdov et al. Electronic Digital Computers. Moscow, Voenizdat, 1968.

2. A. V. Trikhanov et al. On the calculation of the magnetic-tape storage unit of a digital recording system. In the present collection.

3. Universal Digital Computer M-220M. Technical Description, OYa1.320.017.TO, Kazan, 1970.