The Research And Design Of LED Video Display System Based On The DVI Interface

1. Significance of studyThe LED screen is a large scale display system including micro-electron,light-electron, computer and information processing technology. It has some uniqueadvantages of brilliant color, widely dynamic range, high brightness, long lifetimeand stable performance. Now its application facet is extremely broad such asadvertisement, securities, information dissemination, news issue, etc. It can displayall kinds of multimedia communication including character, figure, animation anddynamic video.During the whole LED display system, there are many digital signals whichare transmitted, disposed and controlled. At present the VGA analog interface iswidely used between the computer and display. If the LED screen is used as thedisplay terminal of computer, every image signal of the computer screen must beresolved into three digitized primary color signals which are red, green and bluecolor. But in this way, the treating process is very intricate and some approachesmaybe impact the display effect.With the development of display technique, DVI (digital visual interface) hasbeen brought on. The DVI interface can transmit a great of digital video signals at ahigh speed and it also can be used easily. The working principle of DVI is that itcan transmit digital signals which are generated by display card to the digitaldisplay. The dominant advantage of DVI is that there are no signal losses in thecourse of signal transmission. Further more, it can prevent environment signalsfrom disturbing. At present, the DVI interface has been recognized and supportedby many manufacturers of display adapter and display, so it has a greatly widedevelopment foreground.This paper combines the DVI technology with the LED display screen anddesigns a suit of scheme that can control the display of LED screen by obtainingvideo data from DVI interface.2. Universal Project of the display systemDVIDecodingCircuitFPGAControllerSRAM1SRAM2FPGAControllerSRAM1DriveCircuitLED DisplayScreenFromDVIInterfacedisplay systemSendingsystemReceivingtransfer systemsystemDifferentialSRAM2EthernetsendingEthernetsendingTransformerTransformerFigure 1 Block Scheme of LED Display SystemFigure 1 above shows the block scheme of LED display system. The wholedesign is composed by the following parts: the DVI decoding circuit, sendingcircuit, receiving circuit, transmitting circuit and driving circuit. First, the systemtakes over the difference signals from DVI interface. The system decodes thesesignals by decoding circuit and recovers the video data and control signals whichincluding horizontal synchronizing signal, vertical synchronizing signal, dataenable and pixel clock. Second, the FPGA controller of sending circuit deals withthe high speed data from decoding circuit and intercept relevant video data basedon the design requirement. The data is sub-packaged and regrouped by the FPGAcontroller according to the specially composing mode of LED display screen. Thedata which is divided by the frame is alternately stored in two external storages.Then the video data is converted into the RMII format and sent into Ethernet sender.The Ethernet sender encodes the data and converts it to difference signal that canbe used for long distance transmission. The Ethernet receiver decodes thedifference signal and recovers the video data of RMII format. The FPGA controllerof receiving circuit disposes the video data further and generates the gray scale dataand control signals that can be used in the LED screen. Then the data and controlsignals are been given into the driving circuit. The driving circuit illumes the LEDscreen by the mode of dynamic scan which depending on line scan signals andcolumn data signals.Consequently, the design above is an organic whole and must be consideredcompletely.3. The software and hardware design of the whole systemThe hardware design of the paper can be divided into three parts. The first partwhich is named sending card in the paper, including DVI decoding circuit, sendingsystem and dispatch unit of the transfer system. The second part which is namedreceiving card in the paper, including receiving unit of the transfer system andreceiving system. The third part is the driving circuit.The programmable logic device FPGA is the core of the design. It will makethe whole design have some unique advantages of small bulk, high integrationdensity, high reliability and high speed. Furthermore, FPGA increases mobility ofthe circuit design and make the circuit be prone to debugging and modification. Atthe same time, it shortens the development time and improves system performancemore.DoubleRAMClockCircuitAddress Generatorof Writing SRAMAddress Generatorof Reading SRAMAddressControlModuleofReadingandWritingSRAMDataTransformModuleofReadingandWritingSRAMInterfaceTransformModuleofEthernetSRAM2SRAM1RGBTransformDEVSYNCHSYNC24bit Data Address A16 ~A0Data D7~D0Address A16 ~A0 Data D7~D0clockPixel Data(RGB)ControlSignalSignalSwitchRD[1:0]GD[1:0]BD[1:0]ControlSignalToEthernetSenderFigure 2 Functional Block Diagram of FPGA Controller in the Sending SystemDataProcessingModuleClockCircuitAddressGenerator ofWritingSRAMAddressGenerator ofSubareaReadingSRAMControlModuleof ReadingandWritingSRAMGrayScaleModuleSRAM2Address A16 ~A0Data D7~D0Address A16 ~A0 Data D7~D0ClockRD[1:0]GD[1:0]BD[1:0]ControlSignalR1G1B1R8G8B8BADC o TDriveCircuitofLEDScreenFigure 3 Functional Block Diagram of FPGA Controller in the Receiving SystemThe emphasis of the system software part consists in FPGA controller's design.Figure 2 and Figure3 above show the functional block diagrams of FPGAcontrollers in the sending system and receiving system. The internal logic isconsiderably intricate. The paper mostly adopts a sort of modularized design. It isthat each function of the controller is designed according to the modular mode. Inthis design the EP1C6Q240C8 chip of Altera Corporation's Cyclone family is usedand the hardware description language is adopted to design the controllers.4. Main content of the design1. In this paper we select XGA mode as the video source of the paper. Itsresolution ratio is 1024×768 and refresh ratio is 60Hz. We design the DVI decodingcircuit. We also measure the deferent waveforms of the circuit and analyze thesequential relationship among them. It is very important for designing the disposecircuit between the digital display scope and DVI interface.2. Design the LED display system based on the DVI. We analyze and design itin reason.The sending circuit receiving circuit and interface transition oftransmitting circuit are integrated in two pieces of FPGA, which makes the wholedesign reduced and flexible. It has some unique advantages of good real time andlow cost.We adopt the hardware description language to complete the program,simulation and synthesis.3. Analyze the existing long distance transmission mode and operationalprinciple of video signal. We design rational transmission circuit based on theethernet by selecting the right transmission mode and coupled fashion anddetermining the relevant system parameters. Its goal is to guarantee the stability oftransfer system.4. According to the characteristic and structure of LED, we select anappropriate method to generate the gray level. In addition, the dynamic scan circuitof LED display screen is given in this paper, which includes the column displaydrive circuit and the line scan control circuit.