PROCEEDINGS
OF THE TOMSK POLYTECHNIC INSTITUTE
OF THE ORDER OF THE OCTOBER REVOLUTION AND THE ORDER OF THE RED BANNER OF LABOR
named after S. M. Kirov

Volume 294 1976

RECORDING EXPERIMENTAL DATA

ON MAGNETIC TAPE FOR INPUT INTO THE “M-220M” AND “M-222” COMPUTERS

A. V. TRIKHANOV, A. N. OSOKIN, P. P. GRIGOR’EV, T. G. GRIGOR’EVA

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

Among the scientific and technical problems [1] that must be solved in connection with the automation of scientific research through the use of electronic digital computers, Academician G. I. Marchuk points to the problem of developing scientific instrumentation with mandatory consideration of the possibility of constant communication between the instrument and the computer. From the authors’ point of view, certain aspects of this problem can be solved within the framework of developing devices for recording experimental data in coded form on some medium: punched cards, punched tape, magnetic tape, etc.

A very promising approach [2] for recording experimental results is the use of standard magnetic-tape storage units (MTSU) used by electronic digital computers. Such a tape containing the recorded experimental results can simply be inserted into the standard magnetic-tape storage unit of a computer so that the information can be read from it in the usual manner for a computer. This greatly simplifies and accelerates the input of large volumes of experimental data into the computer.

This approach is feasible when compatible MTSUs are used. Such units include the MTSUs of the domestic machines “M-220M,” “M-222,” “Dnepr,” and others.

For converting continuous electrical signals arriving through two channels (from two sensors) into a digital code, and for recording and storing the conversion results on magnetic tape for subsequent input into the “M-222” and “M-220M” computers by reproducing the information in the MTSUs of these machines, a device has been developed and manufactured for recording experimental data on magnetic tape at the test site.

The device (Fig. 1) is a combination of a two-channel analog-to-digital converter (ADC) with a standard tape-transport mechanism (TTM). In addition, the device includes recording (RB) and playback (PB) units, a magnetic-head unit (MHU), a control unit (CU), and a unit for checking the recorded information (CC).

During an experiment, the ADC sequentially converts the continuous electrical signal of each channel into an 8-bit binary code, which, by means of the recording amplifiers included in the RB, the magnetic-head unit, and the TTM, is recorded in a line of the tape. The sequence of these codes is fixed in the lines of the magnetic tape. Between zones there are interzone gaps in which the zone numbers are recorded. After the experimental results have been recorded, it is carried out איז?

qualitative assessment of the recording. The zone numbers are specified sequentially, and a search for them is carried out. If a zone is found, the results read from the zone by means of the BV playback amplifiers are fed through the BK digital-to-analog converter to the oscilloscope. If the zone is not found, the corresponding signal is issued, and the results from the zone are not output to the oscilloscope.

The control unit is used in an analogous manner when checking the operability of the device before the start of an experiment. In this case it is advisable to use a two-beam oscilloscope. The voltage of a sign-constant sinusoid is fed to one input of such an oscilloscope, and to the other—the result of double conversion (in the two-channel ADC and in the DAC of the control unit). On the basis of the degree of coincidence of the indicated voltages, and also from the zone-search signals, the operator reaches a conclusion as to the operability of the device.

Fig. 1. Block diagram of the system

Standard magnetic-tape storage units of domestic electronic digital computers limit the possibilities for recording experimental data in terms of the time of continuous recording, the conversion frequency in the ADC, and the accuracy of recording.

The intervals of continuous recording time and of absence of recording are determined by the length of the zone and by the inter-zone spacing. To substantially reduce the inter-zone spacing, a new variant of arranging information on the tape is provided, in which the recording of codes in a given zone is combined in time with the recording of the number of the next zone.

For purposes of monitoring, adjustment, and checking, the device has a mode of continuous recording of codes, i.e., without zones, which may subsequently be used for continuous registration of experimental data after the corresponding modernization of the machine, when it becomes possible to play back from the magnetic tape without zones. In this case the stopping of the tape will be carried out according to the signal that the machine’s random-access memory (RAM) has been filled. After the codes from RAM have been processed, the tape is started again, and the cycle is repeated. This possibility of recording experimental results is based on the fact that any six 8-bit codes recorded sequentially in tape lines do not constitute a “machine” word, i.e., a word with a mantissa and order. For the use of an electronic digital computer in processing experimental data, such a mode of playback from magnetic tape would be very useful.

The described registration of experimental results is characterized by equality of the conversion frequency in the ADC \(f_n\) and the line-recording frequency \(f_z\):

\[ f_n = f_z . \tag{1} \]

This means that the speed of the magnetic-tape storage unit is used to the maximum, being limited by the tape velocity \(v\) and the limiting linear recording density \(\rho\):

\[ f_z \leq v\rho . \tag{2} \]

From (1) and (2) it follows:

\[ f_n \leq v\rho . \tag{3} \]

Domestic general-purpose electronic digital computers require input of information in the form of “machine” words. If the formation of these words

... assign to the experimental-data recording device, then the relation will hold

\[ f_{\mathrm{p}} \leq \frac{vp}{6}. \tag{4} \]

The coefficient \(1/6\) is determined by the fact that one 8-bit code, after the indicated formatting, will occupy 6 lines. Combining (3) and (4), we obtain

\[ f_{\mathrm{p}} \leq \begin{cases} vp & \text{without formatting of “machine” words,}\\[4pt] \dfrac{vp}{6} & \text{with formatting of “machine” words.} \end{cases} \tag{5} \]

It is evident that the existing version of data input from magnetic tape in the electronic digital computer is 6 times inferior in speed to the proposed version. Thus, placing information on magnetic tape without taking “machine” words into account is also expedient from the standpoint of the limiting conversion frequency. Along with its advantages, this placement of information is characterized by an additional expenditure of machine time for forming “machine” words and by the need to change the order in which the bits of the code are arranged. The point is that, when information is read from tape into the magnetic-tape memory of the “M-220M” and “M-222” machines, the three high-order bits in the first line of the word are replaced by zeros. In order to reduce the error due to this replacement, in the recording device the codes are written in the opposite order from that used when writing into the machine’s magnetic-tape memory.

According to the well-known Kotelnikov theorem, for one ADC channel it may be assumed that the conversion frequency is equal to twice the limiting frequency of the signal \(f_c\) taken from the sensor, i.e.,

\[ f_{\mathrm{k}} \geq 2f_c. \tag{6} \]

Taking into account the number of channels \(k\) of the ADC,

\[ f_{\mathrm{p}} \geq 2kf_c. \tag{7} \]

After the transformations we have:

\[ f_c \leq \begin{cases} \dfrac{vp}{12k} & \text{when formatting “machine” words in the system,}\\[6pt] \dfrac{vp}{2k} & \text{without formatting “machine” words.} \end{cases} \tag{8} \]

The expressions given make it possible to calculate the principal technical characteristics of the experimental-data recording device: \(v\), \(p\), \(f_c\), \(k\), \(f_{\mathrm{k}}\). However, the parameters of existing tape transports, above all \(v\), substantially limit such a calculation. A tape transport is required with a tape motion speed variable within specified limits, i.e., a tape transport with start-stop or stepwise tape motion.

An important part of the recording device is a two-channel ADC. It is built on “Ural-10” modules and operates on the principle of bit-by-bit balancing. The functional diagram of the ADC (Fig. 2) consists of a register, a pulse distributor, output gates, a digital-to-analog converter (DAC), two comparison circuits, and a signal switch for the comparison circuits. In addition to the DAC and the signal switch of the comparison circuits, the ADC feedback loop includes, when operating on channel 1, the first comparison circuit, and on channel 2, the second. This method of channel switching is distinguished by high accuracy, but has been little studied. The comparison circuits are built on 2T312 transistors and AI301A tunnel diodes [3].

The comparison circuit can operate in the input-voltage range \(0 \div 3.5\) V with a sensitivity of no worse than 7 mV, at an operating frequency not exceeding 800 kHz.

Fig. 2. Functional diagram of a two-channel ADC

The ADC has a conversion time not exceeding 32 µs, and a level-quantization error not exceeding 0.5 and 0.6% in the single-channel and two-channel versions, respectively.

The other characteristics of the recording device are as follows: capacity—about \(3 \cdot 10^6\) eight-bit codes, number of zones—125, initial zone number—1, recording frequency—\(10^4\) lines.

REFERENCES

1. V. M. Glushkov. Prospects for the application of computer technology. In: Interorgtekhnika-66, Ontipribor, Moscow, 1966.

2. V. A. Lvov, N. S. Poleshchuk. A device for preparing experimental data for input into electronic digital computers. TsNII TEI Instrument Engineering, Moscow, 1971.

3. A. V. Trikhanov, A. N. Osokin, T. G. Grigor’eva. A two-channel voltage-to-code converter. Information Sheet No. 42-72 of the Tomsk TsNTI, 1972.