A new method for obtaining display data from LED screenintroductionAs a new display medium, LED display screen is a high-tech product integrating photoelectric and computer technology. With the rapid development of large-scale integrated circuit and computer technology, it has developed rapidly and has been widely used in all walks of life.
In the LED display system, most of the signals used for transmission, processing and control are digital signals. At present, most computers and external display devices are connected through analog VGA interface. The display image information generated digitally in the computer is transformed into R, G and B primary color signals and lines by D / a (digital / analog) converter in the graphics card Field synchronization signal, which is transmitted to the display device through cable. For analog display equipment, such as analog CRT display, the signal is directly sent to the corresponding processing circuit to drive and control the picture tube to generate an image. For LCD, DLP and other digital display equipment, the display equipment needs to be equipped with corresponding a / D (analog / digital) converters to convert analog signals into digital signals.
Although there are many digital display interface products on the market, which have special output interfaces for digital red, green and blue primary color signals and control signals on the computer screen, most of these products have high prices, sometimes there are compatibility problems, and no unified standard has been formed.Therefore, in terms of analog interface, there are two main methods for the display screen to obtain data: one is to collect data through the special multimedia video card for LED display screen provided by the manufacturer to realize the synchronous display of LED display screen and computer; The second is to obtain data by intercepting the analog signal output by the display card, so as to realize the synchronous display of LED display screen and computer. These two technologies have formed products and are applied to the actual work of LED display screen.For the first scheme, the development of science and technology will inevitably lead to the rapid upgrading of various products, and the multimedia video card will be eliminated by the market because of the unnecessary waste of economy and resources due to the continuous technical updating. For the second scheme, the adaptability of the product is very poor due to the constant transformation of setting parameters corresponding to different display cards and resolution settings.
Based on the above situation, this paper proposes a new method to realize the synchronous display of LED display screen and computer, which can completely replace the multimedia video card, so as to avoid some disadvantages of the existing multimedia video card and realize the integration with the international display screen industry standard.Design principle of 2vga conversion interface card
The basic working principle of VGA conversion interface card is: using a / D acquisition technology, directly analog output image information from the general display card, without installing multimedia video card. Convert one analog signal into digital signal through a / D converter and send it to the display screen; After another analog signal passes through the video preamplifier, it is still sent back to the CRT display in the form of analog signal, which can keep the display content of the display consistent with that of the LED display in real time, and monitor the acquisition effect at any time. The adoption of a / D system also reduces the complexity of installation and operation. As a peripheral of the computer, VGA conversion interface card can be "installed without startup", so as to improve the compatibility of the whole system. Its principle structure block diagram is shown in Figure 1.
3 selection of analog-to-digital conversion chip Analog digital converter (ADC), as the main device constituting the conversion interface card, its main function is to convert the input analog quantity into the digital quantity that can be recognized by the large screen . We use the latest high-speed analog-to-digital converter ad9884a-140 for RGB video launched by American ad company.Ad9884 is a high-speed (500MHz analog bandwidth) 8-bit A / D conversion chip dedicated to intelligent VGA, SVGA and XGA display conversion. The internal register of the chip shall be initialized by single chip microcomputer, and the predetermined working mode shall be written in serial mode. After writing, ad9884 starts to work.
To make good use of a new device, we must first understand the working principle, performance index, limit working parameters and typical circuit connection of the device. If it is an intelligent device, we should also understand its programming characteristics and parameters, and can buy it in the market.The analog-to-digital converter ad9884a is the main chip of the interface card, and other devices should be selected around this chip.3.1 device operating characteristics?