With the rapid development of digital technology, a variety of digital display also emerged there led, LCD, DLP, etc., a variety of digital large-screen control system variety, useful ARM + FPGA offline control system, but also useful PC + DVI interface decoder chip + FPGA chip online control system, where we talk about a not only can be used to control the full-color LED large screen display, but also can be used as a transmitter output high-definition image data. Using the online control system for full-color LED large screen control. That is, PC + DVI interface decoder chip + FPGA chip + output interface mode of the online control system.
DVI interface, called Digital Visual Interface, which is based on TMDS electronic protocol as the basic electrical connection, transitionMinimizedDifferentialSignaling, to minimize the transmission of differential signals. TMDS is a differential signaling mechanism that can encode pixel data and pass it over a serial connection. The digital signal generated by the video card is encoded by the transmitter according to the TMDS protocol and sent to the receiver through the TMDS channel, which is decoded and sent to the digital display device.
The current DVI interface is divided into two, one is DVI-D interface, can only receive digital signals, the interface is only 3 rows and 8 columns a total of 24 pins, one of the upper right corner of the pin is empty, not compatible with analog signals.
The other is a DVI-I interface that is compatible with both analog and digital signals. Compatible simulation Fortunately, does not mean that the analog signal D-Sub interface can be connected to the DVI-I interface, but must be through a conversion connector to use, the general use of this interface graphics card will be associated with the conversion adapter.
The interface used in this paper describes the DVI-D full data interface. FPGA control full color LED large screen system principle and DVI decoder chip control principle.
The input section shows the FPGA chip control decoder chip, the selected FPGA chip is Xilinx's Spantan_3 series X3C1400A-5, the chip can achieve the maximum clock for DDR_SDRAM 200MHz control. The DVI decoder chip used in this system is a decoder chip produced by TI company chip type tfp401 which receives the encoded image data transmitted by the computer DVI interface and outputs it to the DVI decoder chip, which serial data (Red), G (Green), B (Blue) three primary colors of parallel data, and line synchronization, field synchronization, data enable and clock signal, and then the decoded RGB image data, line synchronization, field Synchronization, data enable and clock control signals to the FPGA chip, the image data buffer to the FPGA chip FIFO, it should be noted that when the resolution of the collected image is very large, the data transmission clock signal up to 165MHz , The output of the parallel image data for the 24-bit data, so the maximum bandwidth of up to 3.96GHz, in the choice of external memory is to consider the bandwidth requirements.
Two output interface modes for different areas
①FPGA chip output connected to the drive current chip
The use of the interface is suitable for the output of the multi-drive current chip, FPGA chip output pin timing control multiple external drive current chip, drive the current chip and then control the RGB light-emitting diode, and finally the entire computer want to display the image Displayed on large screen LEDs.
② The receiving end is the interface of the Ethernet cable
The interface is suitable for the input of a DVI decoder chip interface image output, the interface can be used for long-distance transmission of image information, used in large-screen LED display.
Display device using DVI interface advantages. DVI transmission is a digital signal, digital image information without any conversion, it will be directly transmitted to the display device, reducing the number of analog to the digital cumbersome conversion process, significant savings in time, so it's faster , Can effectively eliminate the phenomenon of smear, the use of DVI for data transmission, the signal does not decline, the color is more pure, more realistic. The internal transmission of the computer is a binary digital signal, the use of VGA interface to connect full-color LED large-screen display, you need to first signal through the D / A converter to R, G, B three primary colors and lines, field synchronization signal , These signals through the analog signal line to the full-color LED large screen, but also the corresponding A / D converter will once again convert the analog signal into a digital signal in order to show the full color LED large screen images. In the above D / A, A / D conversion and signal transmission process in the inevitable loss of the signal and be disturbed, resulting in image distortion or even display error. DVI interface without these changes, to avoid the loss of the signal, so that the image clarity and detail performance have been greatly improved.