The presence of a teletext decoder on the TV allows you to view hidden text information broadcast along with the video signal. Using this function, you can read the TV program guide, news, and other materials directly from the TV screen, without looking at newspapers or the Internet.
Instructions
Find a button on your TV remote control with an icon in the form of a stylized screen on which there are three or four lines simulating lines of text. If you press it once, the TV will switch to teletext mode with characters superimposed on a black background. The second press will select the mode for overlaying characters on the television image. Finally, a third press will turn off the teletext mode, and so on in a circle.
Check how the TV behaves when you try to switch to teletext mode, if the this moment channel text information absent. Some devices show a splash screen with information about the absence of a teletext signal, while on others the decoder turns on anyway and displays a blank page. The ability to tune the TV to one channel and read text from another is not available on the vast majority of TVs.
To turn off the decoder at any time, press the key that shows a blank screen.
Use the volume keys as usual, taking into account that in teletext mode information about the value of this parameter is not displayed on the screen. The sound in the speakers is heard from the channel to which the TV is tuned.
Use the channel switching keys and number keys to select teletext pages. Remember the numbers of two pages, which are standard on most channels: 100 - title page, 888, or, less commonly, 777 - subtitles. Immediately after turning on, the decoder waits for page 100 to appear. All pages have three-digit numbers, and they do not have numbers less than 100. The number of the page currently broadcast is displayed at the top. As soon as the page with the number you selected is transmitted, it will load immediately. If it is missing, the counter will spin endlessly until you enter another number. The absence of page number 777 or 888 indicates that the program is not accompanied by subtitles. Subtitles are always displayed on top of the image rather than a black background, regardless of the selected mode.
If a quiz is displayed on the screen, you will not see the answer to the question until you press the question mark key. To remove the answer, click on it again.
At the bottom of the page, four colored rectangles are displayed with the numbers of other pages to which the displayed one links. To follow the link, press the corresponding color key on the remote control.
Remember that when the decoder is turned on, changing channels, entering the TV menu and some other functions are blocked. To use them, exit teletext mode.
The presence of a teletext decoder on the TV allows you to view hidden text information broadcast along with the video signal. Using this function, you can read the TV program guide, news, and other materials directly from the TV screen, without looking at newspapers or the Internet.
Instructions
Sometimes an LG TV user needs to activate subtitles while watching a video; unfortunately, not everyone can do this; it is quite difficult to figure out the numerous settings on your own, especially for modern, multifunctional TV models. IN this review we will look at how to enable and disable subtitles on LG TVs.
The process itself may vary slightly depending on specific model TV, but in any case you can control subtitles using the remote control remote control.
How to turn on subtitles while watching a video on TVLG
While watching a movie recorded on a flash drive or removable media, you can activate subtitles in any language, or disable existing captions at the bottom of the screen. When you start watching a movie or video clip, you will need to click on the button with an arrow, it is located in the center of the screen, on the right side. Next, follow the “show” section additional elements management.
- Remember, if you can’t remove subtitles on your TV at all, that is, they accompany every movie and you can’t find a way to turn them off in the settings, it may be outdated software TV, or there is a virus in it, in this case you will need to seek help from specialists LG service center.
After this, you will need to click on the section called “SUB” and select the subtitle option: “external...” or “internal...”. Having made your choice, click on the appropriate menu mode and select a language, this option will appear on your screen. To be able to select the subtitle language, pay attention to the version of the desired movie when you download it to a flash drive; it should initially contain similar files.
In addition, some models of old TVs, or rather their control panels, are equipped with a special key, it is called “subtitle” or “sub-t”. Of course, there is no such functionality for setting up and displaying subtitles, but by pressing just one button you can activate or deactivate them.
For many television channels a variety of additional information is now transmitted in the form of teletext. How are teletext signals transmitted? How to take them? What options are there for building decoders? The published article answers these questions. The author also talks about software and working with the remote control in various modes, about possible distortions, how to eliminate them and, finally, how to ensure reception of teletext systems in old televisions.
Teletext is Information system for the mass user, ensuring the transmission of a wide variety of information to TV owners in addition to regular television programs. The literature on this issue available to radio amateurs contains only fragmentary information of a general nature. To fill this gap, we will try to take a closer look at the organizational, technical and operational aspects of the functioning of the teletext system.
The development of the principles of operation of such systems, the formation and transmission of signals in them, and the designs of transmitting and receiving devices began in the 60s almost simultaneously in England, France and Germany. The most rational option turned out to be the one proposed by the British Air Force Corporation, and it is currently used as the global standard WST (World System Teletext). The French Antiope system saw only limited use.
Information transmitted using the WST standard can be text or graphic. It is formed at the television center in the form of pages numbered from 100 to 899 and grouped into so-called magazines. Each of them is dedicated to a specific topic, for example, sports, economics, etc. It contains about a hundred pages. The first page contains the table of contents (list of sections of the magazine). Typically, a section, such as a train schedule, consists of several pages.
To receive information from the teletext (TXT) system, the owner of the TV must tune it to a program hosting such a program, and, switching to receiving TXT signals, call up page 100 with a list of magazines. Then, having selected and called up the desired magazine, view its table of contents and call the desired section on the TV screen for viewing. This is the general algorithm for obtaining information in the TXT system.
There are several options for its implementation. This is LIST mode and requires all of the above steps to be completed. There are modes with a simplified procedure: FAST (fast, convenient teletext), FLOF (Full Level One Features - one function for all levels, which, loosely translated, means calling all pages with one button), TOP (Table of Pages - list of pages). In some regions, the less common systems Antiope, Safari, and Spanish Teletext are used.
The main differences between these modes are the nature of the connections between pages and the way they are searched.
In the LIST and TOP modes there is no such connection; the pages are independent and are called up by their numbers. However, if one of the pages of a multi-page section is called up, a message about the presence of a continuation and the number of pages in it is displayed along with it (they are called subpages). The difference between the LIST and TOP modes is that in the LIST mode, to call up a page you need to dial its number on the remote control, and in the TOP mode, a menu is used (a list of pages on the screen), on which the cursor is placed (controlled from the remote control) opposite the line with the name of the desired journal or section.
In FLOF mode, all information is grouped into four topics, and the remote control has four colored buttons to call them up. When you click one of them, all pages of the topic are displayed sequentially on the screen one after another. Page changes can be paused for analysis and then continued or stopped.
In FAST mode, page enumeration is organized differently. On the first page of each magazine, in addition to the list of sections and page numbers, there are four colored fields with page numbers. Each field corresponds to a button of the same color on the remote control. When you press it, the page whose number was indicated in the selected field is called up (without dialing a number). This page also has fields, but with different numbers. By doing this, you can get to the desired section and page in just a few steps.
However, in any mode, each page can be selected using the method used in LIST mode - by dialing its number.
Despite the abundance of modes for implementing the information search process, each telecentre can use only two methods: LIST and one of the fast modes (FAST, FLOF, TOP). At the same time, the receiving side must be capable of multi-mode operation to receive messages from any telecentre.
A WST standard TXT page consists of 25 lines of 40 characters per line. The first line is the page title. Lines 2-25 contain TXT information, and in FAST and FLOF modes, line 25 serves as the status line.
The header contains the page number owner on the screen; number and name of page W, currently transmitted by the television center; date and time of transmission; number and numbers of subpages. The status line displays colored fields with topic names (FLOF mode) or page numbers (FAST mode).
Any string is transmitted as a series of 45 bytes. Bytes 1-3 are synchronizing. Bytes 4, 5 represent the line address: the log number and the line number in the page.
Bytes 6-45 of the header are used as follows: 6, 7 contain page number N; at 8-11 - date and time; at 12-45 - the number and title of page W, as well as symbolic information displayed in the header (day of the week, etc.). The same bytes in other lines contain character information of the transmitted text. To improve noise immunity, the eighth bit of each byte is given a value that ensures an odd number of ones in the byte. The string address is bit protected.
TXT information, prepared for transmission by a special television center service, is digitally stored in a data bank, from which it is cyclically extracted and page-by-page entered into the television video signal (PTTV). Page transfer occurs during vertical blanking pulses (CHPs).
Let us recall that the CGI of the first half-frame (field) of the PCTV occupies the interval from the 623rd line of the previous field to the 23rd line of the first field, and the second field - from the 311th to 335th lines. Some of them are already occupied by equalizing horizontal pulses, color synchronization signals of the SECAM system and television test signals. Only 12 lines with numbers 6, 16-18, 22, 23, 318, 319, 329-332 are free in each frame. This is where the TXT signals are placed.
In Fig. Figure 1 shows the oscillogram of the PCTV during the transmission of OCG and the position of the TXT signals in it. There are two vertical axes on it: the level of instantaneous power p emitted by the transmitter, and the level of the brightness signal Y corresponding to this power. Since domestic broadcasting is carried out using negative modulation, zero values on these axes are located at different levels, and the axes are directed in different directions.
The TXT string is transmitted in the interval between two horizontal blanking pulses. This interval is 52 µs, and during this time 45 bytes (360 bits) of information must be transmitted. Therefore, their transmission speed must be at least 6.923 Mbit/s. The WST standard assumes that a series of bits in the TXT string are transmitted as square wave signals with a pulse and pause duration of 0.144144 μs. A bit with a value of 1 corresponds to a signal with a level of 80% of the PTTV brightness, and a bit of 0 corresponds to 30% of the brightness. These signals occupy a frequency band of 4...10 MHz, which goes beyond the PTTV spectrum, which is limited in different systems broadcasting frequency 5...6 MHz. To introduce them into the PTTV spectrum, the subcarrier of the teletext signals is shifted to a frequency of 3.46875 MHz (harmonic 222 of the horizontal frequency), and the upper sideband is suppressed.
When using one TV line per half frame to transmit TXT signals throughput according to the WST standard, it is equal to two TXT lines per frame or 0.5 s per page.
This is the structure and order of encoding lines of TXT pages in our SECAM-D/K broadcast system. The PAL system does not have special color bursts, and pages can be transferred faster by using more TV lines. The NTSC system uses a different system for placing TXT signals in the PTSD, and in some countries a different number of lines per page and characters per line are used. The Antiope system uses a different string format. More detailed information about these systems is contained in.
In our country, TXT programs are broadcast on ORT, TV Center, NTV, TV-6 and channels satellite television. Each of them forms its own package of magazines and determines their content in its own way.
Thus, ORT transmits a package called “Russian teletext service on TV channel 1 TELEINF” of five magazines: news and sports, economics and finance, goods and services, leisure, kaleidoscope. The package contains pages numbered from 100 to 512. On page 100 the table of contents of the package is given: the names of the journals and the numbers of their first pages. On page 101 the frequency of updating information in the package is indicated: news - twice a day; weather, finance, sports, TV programs - daily; other information - two to three times a week.
The package is organized in FAST mode, but colored fields are only available on the first pages of sections. The selection of subpages in some sections occurs automatically; in others, subpages need to be called up by dialing a number. The waiting time for the next page does not exceed 45 seconds.
Teletext on the TV Center program is organized in LIST mode. The package of pages numbered 100-497 is structured so that the first pages of the magazines and pages with the most important information transmitted several times in each cycle. This significantly reduces the waiting time for such a page, although for others it is the same as in the ORT package.
The NTV program broadcasts the "Magazine of Business People BLITTEXT", consisting of pages 100-777, also in LIST mode. The TV-6 text package is transmitted in the same mode on the TV-6 channel. It consists of three magazines. Its peculiarity is that the search for pages is carried out only within the page numbering of the called journal. This means that in each half-frame of the PCTV, one line from each log is simultaneously transmitted. The page wait time does not exceed 5...8 s, which is much better than this indicator in any other program.
To receive TXT signals, the TV must have a special device - a TXT decoder, and to control its operation - a remote control system with microcontroller command processing and appropriate software. Let's start looking at them with the TXT decoder.
There are a large number of types of decoders, which differ in the way they control their operation, the amount of page memory and circuit design.
According to the control method, decoders are divided into simple and with advanced capabilities. A simple decoder is controlled by a microcontroller (CCU-TV) of the TV control system. It only works in LIST mode. The decoder with advanced capabilities provides operation in both LIST mode and fast modes (FAST, FLOF, TOP). To do this, it must have its own microcontroller (CCU-TXT). Let us recall that a microcontroller is an eight-bit microprocessor, the housing of which contains a set of interface devices that convert machine codes of the microprocessor into analog or other forms of signals for controlling external devices, including a digital bus.
Based on memory capacity, decoders are divided into single-page (UNITEXT), four-page, seven-eight-page (EUROTEXT), ten-page and more (meaning the number of pages simultaneously memorized when a page number is dialed).
The circuit design of teletext decoders (TCT), despite the large number of models, has only a few basic options.
The first of these will be the MST-601 voltage synthesizer and decoder module. It consists of a PII remote control signal receiver, a CCU-TV microcontroller with a PROM-TV memory unit and a decoder. The block diagram of the module is shown in Fig. 2.
The CCU-TV microcontroller (DD1) receives and processes commands to control the reception of television programs and teletext. The procedure for processing commands related to TV control processes (turning on/off, switching programs, adjusting analog parameters, displaying information on the screen - OSD) is described in. As for teletext control, this chip has built-in software (software) of the CTV322S variant, which allows you to control a simple decoder directly, and a decoder with advanced capabilities through its microcontroller.
A four-page decoder with advanced capabilities of the MCT-601 module operates in LIST and FAST modes. It contains five microcircuits: a CCU-TXT microcontroller with a PPZU-TXT memory unit, a VIP2 video processor, an ESST driver with a RAM-TXT memory chip.
The CCU-TXT microcontroller processes teletext control commands received via a two-wire I2C bus from CCU-TV (a description of the structure and operation of the bus is given in), writes information from the page headers to the EEPROM-TXT (DD4) and ensures that the page number is determined when the colored button on the remote control is pressed .
The module uses three memory chips. The PROM-TV stores the tuning parameters for television programs generated by the CCU-TV, and when working with a simple decoder, the TXT page numbers. ROM-TXT is required only in decoders with advanced capabilities for storing TXT page numbers. RAM-TXT contains the texts of pages selected by the TV user from their stream.
In the UNITEXT decoder, the list of page numbers for each program consists of one number, in a four-page decoder - of four, and in EUROTEXT - of eight numbers. The same number of page texts for one selected program is stored in RAM-TXT.
The capabilities of control systems for televisions of different brands in terms of the number of memorized settings for television programs and teletext decoders for programs transmitting TXT are determined by the memory configuration of PPZUTV and PPZU-THT. For four-page decoders controlled via the I2C bus, the configuration options listed in Table 1 are possible. Depending on the chosen option, PCF8571/81 128-byte or PCF8570/82A 256-byte chips must be used. To ensure that the CCU can recognize the selected configuration and correctly address commands, the memory chips have the following: 1 addresses. The address of the microcircuit is set by the voltages on its pins 1-3. To assign a JSC address, you need to connect all these pins to a common wire. At address A2 or A4, a voltage of +5 V is applied to pin 2 or 3, respectively, and the remaining pins are connected to the common wire.
Table 1
| Availability and type of teletext decoder | Number of memorized programs | Memory capacity and chip addresses | ||||
| PPZU-TV | PPZU-TX | |||||
| TV broadcasting | with TXT transmission | Memory capacity, bytes | Address | Memory size, bytes | Address | |
| Absent | 40 90 | - - | 128 256 | A4 A2 | - - | - - |
| Simple | 40 90 | 16 16 | 128 256 | A4 A2 | - - | - - |
| With advanced features | 40 40 90 90 | 16 32 16 32 | 256 128 256 256 | A4 A2 A4 A2 | - 256 128 256 | - A4 JSC JSC |
The full color television video signal of the PCTV, containing TCT information, from the video path is supplied to pin 27 of the VIP2 (DD5) video processor - a specialized SAA5231 chip (analogue - KR1087XA7). PTSD processing in VIP2 consists of extracting synchronization signals (VCS) and synchronously detecting the 3.46875 MHz subcarrier. The resulting TTD teletext signals are amplified and limited. They represent sequences of pulses and pauses of various durations transmitted during CGI - current display of digital codes of symbols of lines of TXT pages. To decode (digitize) signals of this kind, it is necessary to have a parallel synchronous and in-phase stream of synchronization pulses (TTD) with a frequency equal to or a multiple of the maximum repetition rate of TTD signals.
The TTS pulse repetition rate is taken to be 6.9375 MHz. It is formed in the VIP2 video processor by dividing the signal frequency of the generator with a ZQ3 quartz resonator into two. This ensures synchronization of TTD and TTC streams. Their in-phase is established by adjusting the phase of the TTS signal by the PLL system available in VIP2 when comparing the three-level SSC gate pulses entering VIP2 from the ESST driver with VCS pulses extracted from the PCTV.
If the PCTV has insufficient swing, the operation of the PLL system becomes unstable and instead of VCS pulses, an artificial TCS clock signal generated in the ESST is used to control it. Switching VCS pulses to TCS at the input of the PLL system is provided in the VIP2 video processor by the PCTV level analysis unit.
Signal processing in VIP2 occurs at a frequency of 6.0002 MHz, generated by a generator on the ZQ4 resonator. Pulses of this frequency (F6) are also transmitted to the ECT to receive the TCS signal. At the same time, TTD, TTC, VCS signals pass through ESST from VIP2.
The signal generator R, G, B of the teletext ESTT (chip SAA5243 P/R or analogue KR1568VG2) ensures the selection from the TTD, TTC streams of those parts that relate to pages to be written to memory and displayed on the screen. The extracted pulses are divided into eight-bit groups corresponding to character bytes, which are then converted from serial to parallel codes. In this form they are written in RAM page texts (RAM-TXT) via the eight-bit DO-D7 bus. In total, in the RAM-TXT of the four-page decoder MCT-601, with each dialing of page number N on the remote control, four pages with numbers N-1, N, N+1, N+2 are written. For each of them, 24 (according to the number of lines in the page) sets of 42 bytes of TTD signals and 42 bytes of TTC signals are entered. Total - 2016 bytes (the memory capacity of the DD7 chip is 8 kbytes or 8192 bytes). The first three synchronization bytes of the line are not written to RAM-TXT.
The placement of these sets of signals in RAM-TXT is controlled by the ESST driver via the 13-bit address bus AO-A12. Then it displays from RAM-TXT information related to page number N or (on command from the remote control) N+1, N+2. Information on page N-1 in the MCT-601 module can only be displayed in FAST mode.
The conversion of output signals from machine codes into symbolic form occurs in the character generator available in ESST. This character generator (similar to the CCU-TV character generator), in addition to converting codes, generates the brightness value of the pixels of the image matrix of the desired symbol, and then deploys these brightness signals along the television lines in the place where the symbol should be located. Details of his work can be found in the section "84С44&№42;&№42;, 84С64&№42;&№42;, 84С84&№42;&№42;" reference book.
The R, G, B and FB teletext signals generated in ECST, together with the same OSD signals from CCU-TV, pass to the R, G, B DD8 signal switch (made on SN74LS241 or an analogue of KR1533AP4). This microcircuit is a two-channel buffer amplifier (four amplifiers in each channel) and when the outputs are connected in pairs, it forms a switch. It transmits TXT and OSD signals to the TV's video processor for output after they are added to the screen.
To ensure a stable position of the TXT page on the screen, it is necessary that the frame scan trigger pulses KIzap and the frame components of the VCS, TCS signals are in phase. Otherwise, an unpleasant vertical jitter of the page text occurs. To eliminate this phenomenon, the position of the pulse fronts (CIzap) is corrected by POE pulses generated in the ESST and transmitted to the frame scanning unit of the TV.
The MST-601 module is used in HORIZONT-STV601/602 TVs together with the PDU-6 or PDU-6-1 remote controls. The schematic diagram of the module was published in.
Simple decoders operating only in LIST mode were also built according to the circuit shown in Fig. 2. An example of them is the MDT-655 teletext module, used in the HORIZONT-CTV655 and TVT2054TX/2154TX TVs. It does not contain CCU-TXT and PPZUTXT (DD3 and DD4 in Fig. 2, circled with a dashed line). The connection of the remaining microcircuits and their functioning remained the same. The MDT-655 module uses a CCU-TV of the same type as the MST-601, but of a different modification: RSA84S640R-030. Both microcircuits have the same characteristics and pinout, but different software. Modification 030 has the CTV320S software installed, which differs from the CTV322S in the absence of control over the “Frame in Frame” module. The ability to control the TXT decoder is the same for software and chip modifications. By the way, the CTV320S software also has modification 019 of this chip, which can serve as a replacement for PCA84S640P-030. The schematic diagram of MDT-655 is discussed in.
For use in the HORIZONT-CTV655 TV, a teletext module with expanded capabilities MDT-656 was developed. His diagram is also presented in. Compared to the device according to the diagram in Fig. 2, instead of VIP2 and ESST, it uses the SAA5281ZP/R teletext processor, which replaces these two chips. The limitations of the functions performed by CCU-TXT led to the fact that they were later transferred to more complex LP processors, which combined CCU-TXT, VIP2, ECT in one package. This simplified decoders while maintaining multi-mode operation.
A decoder built using such a SAA5246P/R chip is used in TVT2594TX/2894TX. His structural scheme shown in Fig. 3. TXT signal processing technology corresponds to that described above. The number of quartz resonators has been halved. The circuit diagram of the decoder is given in. This design of decoders was used by SONY in the KV-M14 model and by GRUNDIG in devices with a SAA5273 processor. A Russified version of the decoder for SONY-KV-M14 TVs is produced by the domestic company Komplekt under the designation TTK-10.
The next step towards improving decoders was the combination of CCU-TV and the TXT processor. With the advent of such microcircuits, the TV control system and decoder turned into a single-chip (except for memory chips) module. Let us recall that the first models of TV control systems contained two dozen microcircuits and another ten microcircuits were in the TXT decoder.
There are several types of such chips, in particular SDA5250 and SAA5296. The first is used in the control system and decoder of TXT receivers SONY-KV-21X. The block diagram of the system is shown in Fig. 4, a circuit diagram given in . The difference between the decoder and those previously discussed is as follows: from pins 45-48 the R, G, B, FB signals of both OSD TV programs and TXT are removed (the switch of these signals to common pins is located in the microcircuit). The processor uses two external memory chips RAM-TXT (DD3) and PROM-TV, TXT (DD2), as well as five internal memory blocks: RAM control commands, RAM TXT pages, ROM of the combined character generator OSD and TXT, ROM and RAM of the microprocessor.
The control system and ten-page TXT decoder microcontroller SAA5296 is currently one of the best microcircuits of this type. It has numerous interfaces and software that allow you to control analogue or digital TV any complexity and process the TXT signal in any modes. Information about it and the connection diagram are presented in.
All decoders discussed above are controlled via the I2C bus. Let's talk about decoders that use other buses.
The Ml digital bus was proposed by PHILIPS to control decoders that use the SAA5020, SAA5030, SAA5040, SAA5050 and other simpler chipsets. There are ten chips in the decoder in total. Its typical diagram is shown in. The decoder is controlled by a SAA1251 or SAA1293 chip. All these microcircuits are now outdated, and along with them the Ml bus has fallen out of use.
The IM bus is still used today to control TXT decoders along with I2C. One of the reasons for this can be indicated by the presence of a set of chips that allows the IM bus to implement a simpler construction of a digital color block than is currently possible on chips controlled via the I2C bus. Using the IM bus, TXT decoders with TTD digital signal processing have been created. An example of such a device is the MTT-57 module of ELECTRON-TK551/557 televisions. Its block diagram is shown in Fig. 5, and the circuit diagram is discussed in.
The decoder consists of an analog-to-digital converter ADC DD2, a scan processor DD3, an LP processor DD5 with a memory chip DD6. Its operation differs significantly from the operating principles of the previously discussed devices. The decoder is controlled by commands coming from CCU-TV (DD1) SAA1293A-03 or TVP02066-A26. The PCTV from the video path goes to the DD2 chip, which consists of a synchronous detector, a limiting amplifier and an ADC. The TTD signals obtained as a result of detection arrive at the ADC, where they are converted into groups of seven-bit parallel code corresponding to the bytes of the original TXT signals. These codes pass along the seven-bit VO-V6 bus to the scan processor and without the most significant bit along the six-bit VO-V5 bus to the LP processor.
In the DD3 scan processor (DPU2540/43), synchronization and blanking pulses are extracted from the TTD digital stream, which are then transmitted to the TXT processor. The digital representation of the TTD stream greatly simplifies signal separation. The fact is that horizontal sync pulses are detected by the appearance of ones in the most significant bits of the code at the output of the ADC. The synchro selector in this case is a simple device that selects the V6 bit of the code and turns it into a synchronization pulse of the required shape and amplitude.
Processing of the TTD digital stream in the LP processor ends with the formation of page texts in machine codes, transmitted via the DO-D3 bus to RAM-TXT (DD6) in four-bit words with their addressing via the eight-bit AO-A7 bus. The memory capacity is 128 KB, which allows you to store up to 128 pages. At the command of the remote control, information from RAM is called into the LP processor, which has an internal character generator, and after conversion into symbolic form is transmitted to the video processor of the TV.
The module was produced in two versions: MMT-57 - for operation in LIST, PAST, FLOF and TOP modes and MMT-57-1 for operation only in LIST mode.
The second component of any teletext system is the TV control system: remote control, CCU-TV. digital bus and software. Methods for organizing communication between the TXT decoder and CCU-TV. bus and software were considered when describing decoders. Let's move on to the issues of organizing control of the decoder from the remote control.
There are many different models of remote control. differing in the number of commands, buttons and their purpose. In the RC-5 SDU, used in equipment with a digital l2C bus. To control the TXT decoder, a set of 40 commands is provided. Their complete list is given in. As a rule, only a part of them is used in the remote control, selected at the discretion of the equipment developers. As a result, the decoder control procedure in TVs of different brands turns out to be organized differently.
For analysis, let's take the remote control panel 6, used to control the previously discussed MST-601 module. It has 36 buttons, of which 26 are used to control the decoder. They are shown in Fig. 6 in the form of filled (black and colored) rectangles, their purpose is also indicated there. The remote control allows you to work with information in LIST, FAST and FLOF modes.
When you turn on the TV in operating mode (button 1), the decoder software is automatically set to the starting address and the FAST mode is entered.
In order to start familiarizing yourself with TXT information in this mode, you should tune in to the program that broadcasts TXT in this mode and press button 10 on the remote control. A title bar with number N will appear on the screen. If N#0. you need to press button 7 to call page 100.
When page 100 appears on the screen, the desired magazine is selected and the number of its first page is known, you should dial this number using the "0" - "9" buttons of the dial field 13. If the magazine starts from page 101, then press button 12 to go to it.
On the first page of the magazine, in addition to the table of contents, there is a status line, and in it there are four colored fields (red, green, yellow and blue) with page numbers. On the remote control, press one of the buttons in zone 8 of a color that matches the color of the field with a number equal to or close to the number of the desired page. The desired or some other page with different numbers in colored fields will appear on the screen. Repeating this procedure, you need to go to the desired section. It will scan pages either automatically every 30...45 s. or by calling their numbers.
In order to move on to TXT. transmitted by another program, you need to turn off the decoder with button 10. turn on the desired channel, press button 10 again and. if it also works in FAST mode, proceed like this. as described above, or switch to LIST mode.
The LIST mode is activated by button 2 ("P+"). To return to FAST mode, you need to press it again. When selecting information in this mode, call up page 100 (button 7) in the same way as in FAST mode. Then, using buttons “0” - “9” of dial field 13, dial the number of the first page of the magazine, and after it appears, dial the number of the first page of the desired section. Each time, pages numbered (N-1)-(N+2) are stored in memory. of which page N is displayed on the screen. To pages N+1. N+2 go by pressing button 12. To call up the next group of pages with the continuation of the section, you need to dial the page number N+3 using the “0”-“9” buttons of dial field 13 or press button 12 again. After some waiting, the next four pages will stored in memory, and page N+3 appears on the screen.
In LIST and FAST modes, other operations listed in table are also possible. 2 indicating the necessary actions. More complex operations are also possible: calling up hidden information (buttons 5 and 4). watching a TV program while the decoder is searching required pages in the TXT signal stream. These operations require pressing several buttons on the remote control in a certain sequence and are not performed on all domestic TV channels.
The composition of the CCU-TV software is described in. As for the order of its operation in controlling the teletext decoder, each time the remote control button is pressed, a command to control the decoder is generated, CCU-TV sends it to the 1gC bus at the address CCU-ТХТ and waits for confirmation from it. If the decoder does not have CCU-TXT (no confirmation received). CCU-TV repeats the command to ESST. If confirmation of receipt of the command is not received this time either. CCU-TV recognizes the situation as a lack of decoder, perceives the command as impossible and reports this by forming a yellow rectangle in the upper left corner of the screen.
If the confirmation came from CCU-TXT or ECT. then the CCU-TV processor includes the programs available in it for processing remote control commands to control the teletext decoder and writes the numbers of called pages into the EEPROM-TV. In FAST mode, it generates and transmits the “Set list” command to the CCU-TXT when moving to the next television channel.
CCU-TXT software is represented by standard sets of programs named CTV900/940/970-976/988/990/991S Their main characteristics are listed in. In particular, the PCF84C81 processor (see Figure 2) uses CTV972S software.
Any set of TXT software includes the following standardized software packages: 8/30 - ensuring the operation of the character generator; 24 - serving FAST and FLOR modes 26 - for processing texts with an extended character set (for example, Spanish, the alphabet of which contains 32 characters); 27 - providing connection between pages.
There are five modifications of the 0/30 package depending on the set of languages being processed. They are designated by the symbols A, E, H, K, R in the type of microcircuit containing a character generator. For example, in the SAA5243P/R chip the package processes Cyrillic (Russian and Latin characters), in the SAA5243P/E and SAA5243P/H chips - Latin characters in broadcast systems with a scan of 625 lines, SAA5243P/A - Latin characters with a scan of 525 lines , and SAA5243P/K - Latin and Arabic characters.
Let us dwell on the issue of possible signal distortions in TCT systems. They manifest themselves in instability of reception and disappearance of characters or their replacement by others (for example, Cyrillic alphabet with Latin). Unstable reception occurs when the signal level at the receiving location is insufficient or the sensitivity of the TV is reduced. The disappearance or replacement of symbols is a consequence of increased sensitivity digital signal TCT to pulsed interference and echo signals caused by reflections from local objects and inhomogeneities in the antenna cable. From this point of view, the TXT signal transmission system adopted in the NTSC standard (sub-carrier phase modulation 2.5 MHz) is more resistant to impulse noise and provides reliable reception.
The appearance of interference may also be the result of inaccurate tuning of the TV to the television signal carrier. A tuning shift leads either to a narrowing of the bandwidth (loss of high frequencies in the video signal) or to the penetration of modulated audio components into the FM video signal. In both cases, the decoding of the TXT signal stream occurs with numerous errors that cannot be corrected by the security measures introduced into them. According to the clear, error-free operation of the TXT decoder, the detuning of the receiver local oscillator is ensured by no more than ±250 kHz. The residual detuning value during operation of the APCG system is normalized at a level of no more than ±100 kHz, but in practice it is very often higher. In case of distortion of teletext signals, first of all you need to check the quality of television reception and, if necessary, adjust the TV’s APCG system.
There are other types of distortions. In Fig. 1 it can be seen that the TXT signals are located in the middle part of the image brightness change interval.
corresponding to gray signals. At normal operation beam back suppression systems, they will not be visible on the screen. If the duration of the vertical scan blanking pulses is incorrectly set, light dots from bits 1 of the TXT signals appear at the top of the screen. They will appear in its lower part if the TV has incorrectly set the levels of the frame and horizontal components of the SSC signal or the ratio between them, and therefore the black fixation level.
These phenomena are explained by the presence of TXT signals in PCTV and can occur on any TV, even those without a TXT decoder. Their appearance should be considered as a signal about shortcomings in the operation of the systems for fixing the level, extinguishing and limiting the current of the beams. This may be caused by incorrect brightness adjustment.
Many TV owners set the brightness to a level that produces high white intensity. In this case, the range of reproduced brightness gradations not only decreases, but their entire interval shifts towards higher brightnesses. Black level restoration is achieved by increasing contrast. This distorts the image and contributes to the appearance of the above defect. It is no coincidence that this opinion has already been expressed in a number of publications on this topic. that brightness adjustment should be excluded from the operational functions. It is proposed to ensure the necessary changes at different intensities of external lighting by adjusting the contrast. This topic requires a separate discussion and is touched upon only in connection with possible interference from TXT signals.
In conclusion, I will briefly mention a new direction in the development of the teletext system - the RDS system. Today, such signals are transmitted not only through television, but also through radio broadcasting channels. Such broadcasts in Moscow are conducted by the radio station "Silver Rain", informing listeners about the weather, finances, etc. In radio receivers that have a signal decoder with CCU and software. These messages are displayed in a creeping line on an alphanumeric display. The operation of such devices is based on principles that coincide with those used in television, but on completely different technical solutions.
Let's move on to some practical tips.
If you have an imported TV with a TXT decoder. whose character generator does not contain the Russian alphabet, and whose decoder is a removable module, it should be replaced with a Russified version. Such modules are available for sale for almost all types of TVs. You just need to make sure that the new module is intended specifically for use in your TV. A working new module will work without any adjustment.
If the required model of the Russified module is not on sale or the decoder is mounted on the TV board, it is recommended to replace the chip in it that contains the TXT character generator. for a new one with the P/R index in the designation (see above). Depending on the design of the decoder, these will be ESSTs. LP or CCU. Soldering microcircuits from a board with a large number of pins requires care and special skills.
As for replacing the CCU in a single-chip TV and decoder control system, it seems irrational and impractical. In this case, you will have to come to terms with the need to read Russian text written in Latin characters.
When the TV does not have a decoder, but has a connector for installing it, purchase the Russified version for this model of the device and install the module in it. There is no need to adjust the TV.
If you want to install a TXT decoder in a third or fourth generation TV, you should, in my opinion, opt for the MST-601 module. You will also need a remote control panel-6 and a network switching unit for MST-601. The scope of work to install the module in the TV is identical to that described in)
