System design of full-color LED large-screen image display system base…
Carla De Bernal…
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09.18 11:30
System design of full-color LED large-screen image display system based on FPGA chip control
With the rapid development of digital technology, various digital display screens have emerged, including LED, LCD, DLP, etc. The control systems of various digital large screens are various, such as ARM+FPGA off-line control system and PC+ DVI interface decoding chip + FPGA chip online control system, here we describe a system that can not only be used to control the display of a full-color LED large screen, but also can be used as a sender to output high-definition image data. The online control system adopted controls the full-color LED large screen. That is, PC+DVI interface decoding chip+FPGA chip+online control system of output interface mode.
Overview of DVI interface
The full name of DVI is Digital Visual Interface, which is based on the TMDS (Transition Minimized Differential Signaling, minimized transmission differential signal) electronic protocol as the basic electrical connection. TMDS is a differential signaling mechanism that encodes pixel data and passes it over a serial connection. The digital signal generated by the graphics card is encoded by the transmitter according to the TMDS protocol, then sent to the receiver through the TMDS channel, and then sent to the digital display device after decoding.
The current DVI interface is divided into two types. One is the DVI-D interface, which can only receive digital signals. There are only 3 rows and 8 columns with a total of 24 pins on the interface, and one pin in the upper right corner is empty, which is not compatible with analog signals.
The other is the DVI-I interface, which is compatible with both analog and digital signals. Fortunately, being compatible with analog does not mean that the D-Sub interface of the analog signal can be connected to the DVI-I interface, but can only be used through an adapter. Generally, graphics cards using this interface will have related adapters.
The interface used in this article is DVI-D full data interface.
Principle of FPGA-controlled full-color LED large screen system
1 DVI decoding chip control principle
The input part of Fig. 3 shows the control schematic diagram of the FPGA chip controlling the decoding chip. The selected FPGA chip is the X3C1400A-5 of the Spantan_3 series of Xilinx Company. This chip can realize the control of the maximum clock of DDR_SDRAM at 200MHz. The DVI decoding chip used in this system is the tfp401 decoding chip produced by TI Company. The chip receives the encoded image data transmitted by the DVI interface of the computer and outputs it to the DVI decoding chip. The chip converts the serial data Decoded into 24-bit R (Red), G (Green), B (Blue) three primary color parallel data, as well as line synchronization, field synchronization, data enable and clock signals, and then decoded RGB image data, line synchronization, field Synchronization, data enable and clock control signals are sent to the FPGA chip, and the image data is buffered into the FIFO of the FPGA chip. It should be noted here that when the resolution of the collected image is very large, the clock signal for data transmission can reach up to 165MHz , the output parallel image data is 24-bit data, so the maximum bandwidth can reach 3.96GHz, and the bandwidth requirement must be considered when selecting an external memory.
System design of full-color LED large-screen image display system based on FPGA chip control
4 Two output interface modes applied in different fields
①The output terminal of the FPGA chip is connected to the drive current chip
The use of this interface is suitable for the output of multi-channel drive current chips. The timing of the output pins of the FPGA chip is used to control multiple external drive current chips. The drive current chip controls the RGB light-emitting diodes, and finally the image that the entire computer wants to display Displayed on the large led screen display screen.
② The receiving end is the interface of the Ethernet cabl
This interface is suitable for the output of one-way input DVI decoding chip interface image. This interface can be used for long-distance transmission of image information and is applied to the display of LEDs on large screens
Advantages of display devices using DVI interfac
DVI transmits digital signals, and the digital image information will be directly transmitted to the display device without any conversion, reducing the cumbersome conversion process from digital to analog and then to digital, which greatly saves time, so its speed is faster , Can effectively eliminate the smear phenomenon, use DVI for data transmission, the signal does not attenuate, the color is purer and more realistic. The internal transmission of the computer is a binary digital signal. If you use the VGA interface to connect a full-color LED large-screen display, you need to convert the signal into R, G, B three primary color signals and line and field synchronization signals through the D/A converter in the graphics card. , These signals are transmitted to the full-color LED large screen through the analog signal line, and the corresponding A/D converter is required to convert the analog signal into a digital signal again in order to display the image on the full-color LED large screen. During the above-mentioned D/A, A/D conversion and signal transmission process, signal loss and interference are unavoidable, resulting in image distortion or even display errors. The DVI interface does not need to perform these conversions, avoiding the loss of signals, and greatly improving the clarity and detail expression of the image
conclusio
The FPGA chip implemented in this design system controls the image display system of the full-color large screen, which can not only be used for the display of the small-size resolution (256×192) full-color LED large-screen control system, but also can transmit images through long-distance Ethernet Data, send the image data to multiple receiving boards, and the splicing of multiple receiving boards can be used to display high-definition color images with a resolution (1920×1280) on a large screen.
With the rapid development of digital technology, various digital display screens have emerged, including LED, LCD, DLP, etc. The control systems of various digital large screens are various, such as ARM+FPGA off-line control system and PC+ DVI interface decoding chip + FPGA chip online control system, here we describe a system that can not only be used to control the display of a full-color LED large screen, but also can be used as a sender to output high-definition image data. The online control system adopted controls the full-color LED large screen. That is, PC+DVI interface decoding chip+FPGA chip+online control system of output interface mode.
Overview of DVI interface
The full name of DVI is Digital Visual Interface, which is based on the TMDS (Transition Minimized Differential Signaling, minimized transmission differential signal) electronic protocol as the basic electrical connection. TMDS is a differential signaling mechanism that encodes pixel data and passes it over a serial connection. The digital signal generated by the graphics card is encoded by the transmitter according to the TMDS protocol, then sent to the receiver through the TMDS channel, and then sent to the digital display device after decoding.
The current DVI interface is divided into two types. One is the DVI-D interface, which can only receive digital signals. There are only 3 rows and 8 columns with a total of 24 pins on the interface, and one pin in the upper right corner is empty, which is not compatible with analog signals.
The other is the DVI-I interface, which is compatible with both analog and digital signals. Fortunately, being compatible with analog does not mean that the D-Sub interface of the analog signal can be connected to the DVI-I interface, but can only be used through an adapter. Generally, graphics cards using this interface will have related adapters.
The interface used in this article is DVI-D full data interface.
Principle of FPGA-controlled full-color LED large screen system
1 DVI decoding chip control principle
The input part of Fig. 3 shows the control schematic diagram of the FPGA chip controlling the decoding chip. The selected FPGA chip is the X3C1400A-5 of the Spantan_3 series of Xilinx Company. This chip can realize the control of the maximum clock of DDR_SDRAM at 200MHz. The DVI decoding chip used in this system is the tfp401 decoding chip produced by TI Company. The chip receives the encoded image data transmitted by the DVI interface of the computer and outputs it to the DVI decoding chip. The chip converts the serial data Decoded into 24-bit R (Red), G (Green), B (Blue) three primary color parallel data, as well as line synchronization, field synchronization, data enable and clock signals, and then decoded RGB image data, line synchronization, field Synchronization, data enable and clock control signals are sent to the FPGA chip, and the image data is buffered into the FIFO of the FPGA chip. It should be noted here that when the resolution of the collected image is very large, the clock signal for data transmission can reach up to 165MHz , the output parallel image data is 24-bit data, so the maximum bandwidth can reach 3.96GHz, and the bandwidth requirement must be considered when selecting an external memory.
System design of full-color LED large-screen image display system based on FPGA chip control
4 Two output interface modes applied in different fields
①The output terminal of the FPGA chip is connected to the drive current chip
The use of this interface is suitable for the output of multi-channel drive current chips. The timing of the output pins of the FPGA chip is used to control multiple external drive current chips. The drive current chip controls the RGB light-emitting diodes, and finally the image that the entire computer wants to display Displayed on the large led screen display screen.
② The receiving end is the interface of the Ethernet cabl
This interface is suitable for the output of one-way input DVI decoding chip interface image. This interface can be used for long-distance transmission of image information and is applied to the display of LEDs on large screens
Advantages of display devices using DVI interfac
DVI transmits digital signals, and the digital image information will be directly transmitted to the display device without any conversion, reducing the cumbersome conversion process from digital to analog and then to digital, which greatly saves time, so its speed is faster , Can effectively eliminate the smear phenomenon, use DVI for data transmission, the signal does not attenuate, the color is purer and more realistic. The internal transmission of the computer is a binary digital signal. If you use the VGA interface to connect a full-color LED large-screen display, you need to convert the signal into R, G, B three primary color signals and line and field synchronization signals through the D/A converter in the graphics card. , These signals are transmitted to the full-color LED large screen through the analog signal line, and the corresponding A/D converter is required to convert the analog signal into a digital signal again in order to display the image on the full-color LED large screen. During the above-mentioned D/A, A/D conversion and signal transmission process, signal loss and interference are unavoidable, resulting in image distortion or even display errors. The DVI interface does not need to perform these conversions, avoiding the loss of signals, and greatly improving the clarity and detail expression of the image
conclusio
The FPGA chip implemented in this design system controls the image display system of the full-color large screen, which can not only be used for the display of the small-size resolution (256×192) full-color LED large-screen control system, but also can transmit images through long-distance Ethernet Data, send the image data to multiple receiving boards, and the splicing of multiple receiving boards can be used to display high-definition color images with a resolution (1920×1280) on a large screen.