Dendy is a TV test signal generator. A new version. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Dendy is a TV test signal generator. A new version. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Телевидение

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A self-made cartridge for the video set-top box "Dendy" [1], which turns it into a test television signal generator (GITS), interested our readers. Thanks to their feedback, the author of the design and program, S. Ryumik from Chernigov, was awarded the incentive prize of the competition "Best Publication of 2001". Today we present GITS-2 - an improved version of the cartridge.

Compared to the first version of the proposed device, its scope has not changed - setting up and adjusting color (working in the PAL system) and black and white TVs, evaluating the quality of a kinescope when buying a TV, and generating test tables for cable television. However, the number of test images created by GITS-2 has been increased from 81 to 466 (taking into account all color options), and sound test signals - from two to four. According to some characteristics, GITS-2 surpasses the well-known generators "Electronics GIS 02T" and "Laspi TT-03".

Since all the functions of the test signal generator are implemented in software, only the program had to be changed during the revision. The hardware part of the device - the actual cartridge board with panels for two EPROM chips - could remain exactly the same as in the original version. Nevertheless, it has undergone a slight improvement, allowing it to work even with partially faulty "Dendy" prefixes.

Scheme of the board GITS-2, shown in fig. 1 differs from the original one in the additional jumper XT3, which is used to switch the screen pages of the "Dendy" video processor.

(click to enlarge)

If one of the video pages in your set-top box is faulty (extra lines or squares are visible on the image), you can switch to another one by moving the jumper and pressing the SELECT button on the joystick. In position "1" the first page works, in position "2" - the second page of video memory.

Drawings of printed conductors and the location of elements on the cartridge board are shown in fig. 2.

(click to enlarge)

The shape of the board was chosen based on the convenience of its installation in a standard "Dendy" cartridge case. A board that is narrower and without side cutouts cannot be fixed in it. Therefore, it is not worth saving material by reducing the width of the board.

The case is taken from a game cartridge that has become unusable. Sometimes you have to modify it a little, for example, to shorten the plastic pins inside.

When developing the GITS-2 program, the author tried to implement the maximum number of tests, occupying no more than 2 KB in ROM. In particular, the image of the test table is stored packed according to the original algorithm. Compression ratio - 50,2% (from 960 to 482 bytes). At the same time, the data unpacker subroutine took only 57 bytes. It would take only 435 bytes to store the same ZIP-packed data, but the length of their unpacker is many times longer.

The codes that must be entered in the RPZU DS1 and DS2 with an information capacity of 2 Kbytes (KR573RF5 microcircuits or their analogues) are given in Table 1, respectively. 2 and XNUMX.

(click to enlarge)

Binary files and files for programming EPROM chips with a capacity of 8 KB (K573RF6 and similar), in which the codes from the table. 1 and 2 are repeated four times in a row.

(click to enlarge)

The properties of GITS-2 (as well as GITS of the first version) do not depend on the type and capacity of the applied RPZU microcircuits, therefore the latter can be combined on the board in various combinations, remembering only to set the XT1 and XT2 jumpers to the desired positions. If you do not plan to replace the microcircuits during the operation of the cartridge, you can connect the corresponding contact pads on the board with ordinary wires instead of jumpers.

On the new board (with the XTZ jumper in the "2" position), microcircuits programmed in accordance with [1] will also work. But you need to use them as a set: both "new" or both "old". Naturally, in the latter case, GITS will have only the properties that were described in the original source.

If there is a ready-made board of the old version of GITS, in order to use all the tests described below, it is enough to install RPZU chips programmed in a new way in its panel.

Those wishing to make their own additions and improvements to the program will be helped article, which describes in detail the methodology for developing programs for "Dendy"

DESCRIPTION OF TESTS

After installing the GITS-2 cartridge in "Dendy" and powering up, a test pattern should appear on the TV screen (top figure on the 1st cover page) and a trill should sound. If there is no image, but there is sound, try moving the XTZ jumper on the cartridge board to another position, press the SELECT button on the joystick. This operation allows you to switch from a possibly faulty video page to a working one. If there is no sound, it is likely that some of the cells of the main RAM of the game console used by the program have failed and further work is impossible.

Due to the peculiarities of the "Dendy" video system, it is difficult to form exact squares on the TV screen (it is not possible to fit into the specified ROM volume). Therefore, in all test images, they look like rectangles with an aspect ratio of 4:5. However, the central circle of the test table has a regular shape, which makes it possible to evaluate the geometric distortion of the raster and adjust its dimensions. In addition, the table allows you to center and focus images by five fiducial marks in the center and corners of the screen, check horizontal and vertical clarity (200...250 lines on a fine grid). There are sections with a chess field, colors, diagonal lines. When pressing the UP, DOWN buttons of any of the joysticks, the image is inverted (the second figure from the top on the 1st cover page), inscriptions in small print appear in the center, top and bottom of the screen.

The next 11 test images are navigated using the LEFT and RIGHT buttons. Each has four options, switched by the UP and DOWN buttons. The options, in turn, have from two to 24 varieties: with button A they change the color of the image, with button B they invert it or turn on / off the fine grid superimposed on the main image. The START button switches sound test signals. The transition from one test to another is accompanied by the sound "beep", and the beginning of a new cycle of their change - a trill.

Dendy is a TV test signal generator. A new version Vertical colored stripes (Fig. 3, a) - eight stripes of the same width in the following order (from left to right): white, yellow, blue, green, purple, red, blue, black. They allow you to check the correctness of the matrix, adjust the pre-distortion correction contours, and evaluate the color saturation in adjacent lines. Shades of the generated colors depend on the features of the "Dendy" video processors of different models and may vary slightly. Options: replacing primary colors with secondary ones, turning off the color (gray scale, third picture from the top on the 1st cover page). Varieties: The letter C on a blue stripe for ease of identification.

Horizontal colored stripes (Fig. 3, b, c) - eight stripes similar to vertical ones, but the lowest one is half as high.

Uniform gray field. Allows you to check and adjust the static white balance, color purity. Options: four gradations of brightness. Varieties: cyclic image inversion with a period of 2 s, which allows you to check the quality of image size stabilization and the stability of frame and line scanning synchronization. Pressing and holding button B quadruples the flashing frequency.

Uniform red field. Serves to check the purity of color, to detect defects in the kinescope mask (there should be no white dots on the image). Options: four gradations of saturation. Varieties: "flashing" with a period of 1 or 2 s.

A uniform green field is similar to a red one.

A uniform blue field is similar to a red one.

A chessboard of black and white rectangles (16 columns, 15 lines) allows you to evaluate the linearity of scans, geometric distortions of the raster, and check the absence of color fringing. Options: image inversion, doubling the size of the rectangles (bottom picture on the 1st cover page). Varieties: a fine grid superimposed on the image, replacing white with one of 12 possible colors (Fig. 3, d).

Monochrome stripes ("sailor suit", Fig. 3, e) serve to assess the linearity of the sweep and the uniformity of coloring of extended sections of the screen. Options: vertical or horizontal stripes, doubling the width of the stripes, image inversion. Varieties: a fine grid superimposed on the image, replacing white with one of 12 possible colors (Fig. 3, f).

Point field (Fig. 3g). White dots (15x16) on a black background with a marker in the center are used to check the focus and astigmatism of the electron beam over the entire screen area, as well as static and dynamic convergence of primary colors. Options: halved or doubled and quadrupled dot pitch (you can choose the optimal one depending on the size of the TV screen). Varieties: image inversion, replacement of white with one of 12 possible colors (Fig. 3, h).

A grid field of 15x16 thin white lines on a black background is used to adjust the convergence of red, green and blue rays, and to check the focus. Options: halved or doubled and quadrupled grid spacing. Varieties: image inversion, replacement of white with one of 12 possible colors (Fig. 3, i, j).

Audio test tones are used to test the sound channel of the TV. The following signals are provided, switched cyclically by the START button: rectangular pulses with a duty cycle of 2 ("meander") with a frequency of 500 Hz, sawtooth pulses with a frequency of 6600 Hz, rectangular pulses with a duty cycle of 4 with a frequency of 6600 Hz, "siren" - "meander" of a linearly changing frequency (from 27 to 12500 Hz for 9 s).

Literature

Ryumik S. "Dendy" - a generator of test television signals. - Radio, 2001, No. 8, pp. 26 - 28

Author: S.Ryumik, Chernihiv, Ukraine

See other articles Section Телевидение.

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