Number formation block. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Radio amateur designer

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The article describes an example of how, using a ROM chip, you can significantly simplify the device, not only retaining its capabilities, but also significantly expanding them.

In "Radio" No. 11 for 1981, an article by V. Kosinov "The numbers on the oscilloscope screen" was published. The block for generating numbers proposed in it is distinguished by an original idea and thoughtful execution. I have repeatedly repeated this device and its modifications with invariably good results. For example, a clock with an indication of the days of the week looks very impressive on the screen of a two-beam oscilloscope.

If the operation of any device can be described using a truth table, then it will completely replace the ROM. Moreover, in the aforementioned digit generation unit, not only the decoder and code converter, but also both shift registers can be replaced by ROM. Wherein:

• the number of microcircuits is reduced by at least 14, therefore, the efficiency and reliability of the device as a whole increases;
• the displayed figures acquire a more "readable" look and become similar to the characters formed on the display screen:
• hexadecimal code symbols are displayed;
• it becomes possible to display any arbitrary character inscribed in a matrix of 4x8 dots;
• it is possible to use multiplexers with both direct and inverse outputs.

The scheme of the improved digit generation block is shown in the figure.

(click to enlarge)

The device contains only nine microcircuits (there are 23 in the original version). Decimal point indication is not implemented here, but this possibility remains. The clock generator is assembled on the elements DD1.1-DD1.3. Dividers by 8 and 5 on counters DD2. DD3, respectively, are designed to form each displayed digit, and the digit capacity of the DD8 counter and the multiplexers used determine the total number of characters on the oscilloscope screen. All other conversions are done with a single DS1 ROM.

Let us briefly repeat the description of the principle of the formation of numbers proposed by V. Kosinov. Each sign is presented in the form of an inclined matrix of 4x8 dots (V. Kosino-va has 4x7 dots) - 8 vertically and 4 horizontally. The matrix is ​​formed due to the relatively slow horizontal movement of the beam, provided by the sweep of the oscilloscope, and the fast vertical step movements that occur when the vertical deviation of the DAC output voltage is applied to the input. formed by resistors R4-R11. The number of vertical steps is 8. It corresponds to one full cycle of the counter DD2. In each sign, four vertical, slightly inclined groups of eight illuminated points are possible (states 0. 1. 2, 3 of the DD3 counter), the interval between the signs is one such extinguished group (state 4 of the DD3 counter).

Vertical scanning of familiarity occurs due to the alternate appearance of a logical 0 on one of the outputs of the DS1 chip. If it is necessary to extinguish any of the familiarity points, a log level is set at all DS1 outputs. 1. In this case, the beam goes beyond the screen of the oscilloscope.

To clear the interval between the familiarity in state 4 of the counter DD3, the transfer of all outputs of the ROM DS0 to a high-impedance state is used at the CE1 input. In table. 1 shows the sequence of movement of the oscilloscope beam when all points of the matrix are indicated, and in Table. 2 - when the number 8 is displayed.

To form all the necessary characters, logical 0s should be written to the ROM at the appropriate addresses, which will determine the position of the luminous dot on the oscilloscope screen. In table. 3 shows the relative addresses of cells in the ROM. in the corresponding bit of which you need to write 0 to highlight the required position 8 in the matrix, and the addresses of such cells for the number "8".

The contents of the ROM to display all characters of the hexadecimal code are given in Table. 4. The five least significant bits correspond to one displayed character, and the address of this character in the ROM is given by the following four binary digits. This address is supplied from the outputs of the multiplexers DD4-DD7.

(click to enlarge)

The amount of memory is enough to describe four different sets of 16 characters. Instead of the one indicated in the diagram, you can use the KR556RT17 ROM in the appropriate inclusion.

Since the size of the digits is 4x7. one of the outputs of the ROM in the proposed device can not be used. To do this, exclude the resistor R4. The eighth, lowest line will not be displayed.

Establishing the device comes down to setting the required frequency of the clock generator (elements R1. C1) and the possible refinement of the resistance of the DAC resistors (R4-R11). With acceptable accuracy, the position of a point on the screen can be selected using two resistors in parallel connection, one of which has the nearest higher rating, and the second with a resistance of 1-20 kOhm.

Author: A.Marievich, Voronezh

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