Application of TW2834 four-channel video controller
Abstract: TW2834 is a four-channel video controller produced by TechWell. This device has a high-efficiency four-channel video analog-to-digital / digital-to-analog converter, with a screen splitter function, and an OSD (on screen display) function. Through the analysis of the TW2834's 0SD function, the paper introduces the design method of using TW2834 chip video to superimpose Chinese character information to realize video surveillance.
Keywords: video controller; Chinese character information overlay; TW2834; OSD
O Introduction Character superposition has been widely used in CCTV, image system, car video system, highway toll system, video surveillance and other systems. TW2834 is TechWell's 4-channel video controller, which is mainly used for video surveillance systems. Using the chip's OSD function, the Chinese character information can be superimposed on the video simply and quickly.
1 Performance characteristics of TW2834 chip TW2834 has four high-performance NTSC / PAL video decoders, two-color display controllers and two video encoders, and it also integrates four built-in analog anti-aliasing filters, four 10
Bit analog-to-digital converter and proprietary digital gain / clamp controller, and high-performance Y / C splitter against cross noise. The TW2834 has a high video zoom function and has four built-in detectors for motion detection and video loss detection. TW2834 has a flexible video display control function, which can flexibly realize the input video at any position on the display screen. In addition, TW2834 also has excellent image overlay functions, such as overlaying Chinese characters, character information, mouse pointer graphics, windows, etc. on the video.
2 The principle of Chinese character superposition of TW2834 The character superposition function of TW2834 is mainly composed of font RAM, display RAM and superimposition control module. Figure 1 is a schematic diagram showing the structure of the RAM.
In addition, the font RAM can store the dot matrix information data of the characters, and the display RAM stores the number, position and attributes of the displayed characters. The size of the displayed characters can be defined by the number of pixels in the horizontal and vertical directions. TW2834 can support 16 pages × 2 (16 pages each in display and record mode) font groups, each font group can support up to 128 characters. When the font dot matrix becomes larger, the number of characters stored in the font group will decrease accordingly.
The font RAM can be understood as a warehouse for storing display fonts, and the display RAM can be understood as a display. When superimposing character information, you should first upload the display font to the font RAM, and at the same time point the area to be superimposed on the font RAM area, so that you can superimpose characters on the video. The structure of its font RAM is shown in Figure 2.
3 Writing of superimposed characters in display RAM In display RAM, the display attributes of each display character include mixing, blinking, color, type, character number, etc., which can be set by 2 bytes of 12-bit data. Each superimposed character line has a font page, font number, horizontal and vertical size and attributes. Through the display attributes of characters and the attributes of character lines, the color, position, size, etc. of superimposed characters can be determined. The display attributes of characters and the display attributes of character lines can be realized by setting the registers of TW2834.
There are 3 different modes for setting the character information of the display RAM, and each mode can carry out data transmission through the serial interface or the parallel interface. The setting mode of the display RAM can be set through the mode control register. There are three setting modes: mode O, mode 1, and mode 2. The specific setting mode is shown in Figure 3.
4 Video character overlay based on TW2834
4. 1 hardware circuit design The hardware structure block diagram that uses TW2834 to realize video character superposition is shown as in Fig. 4. The design of the circuit needs to pay attention to the following aspects:
(1) In this circuit design, the choice of processor should be based on the requirements of the application to select the appropriate microprocessor. The basis for choosing a microprocessor is the processing speed of the microprocessor and the size of the memory, and the functions of the peripheral modules must meet the design requirements. What this design uses is SST89E516R_D2 one-chip computer, this one-chip computer has IAP (programmable in application) Function, has the program memory space of 56K bytes:
(2) The choice of RAM memory chip should be based on the requirements of the system to choose a suitable size of memory. In the application of video overlay Chinese characters, usually only one piece of RAM is needed to store the dot matrix information and other data of the superimposed characters. The size of the RAM will directly affect the number of pages of characters stored in the font RAM. If you want to use TW2834 to superimpose the information in the recording mode at the same time, you need to add an additional RAM
chip:
(3) The function of the font memory is to store dot matrix information of Chinese characters. When the processor receives the overlay command from the host PC, it will take the dot matrix information of the superimposed Chinese characters from the font memory and write it into the font RAM, and at the same time set the display character attributes of the display RAM to realize the superposition of the Chinese characters on the video.
4.2 Writing of Chinese character dot matrix information Using TW2834 to realize the superposition of Chinese character information on the video, the important link is to write the Chinese character dot matrix information into the font RAM. After writing the font RAM, set the display RAM
The display character attribute can realize the superposition of Chinese character information on the video. The flow chart of writing Chinese character dot matrix information into font RAM is shown in Figure 5.
5 Conclusion This paper introduces the method of using TW2834 chip to superimpose Chinese character information on video. This method has important guiding significance for the use of TW2834 chip to realize the superposition of Chinese character information in the video surveillance system. Because the use of TW2834 to superimpose Chinese character information in a video surveillance system has the advantages of simple design, high reliability, and good practicability, it is undoubtedly a good choice to use TW2834 to superimpose Chinese character information on a video surveillance system.
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