![]() ![]() I chose EasyEDA for its supplier integration, as I find it easier to order my components and PCBs through the tool. Feel free to use other PCB design tools such as KiCad, Altium Designer or EAGLE. For my PCB layout, I use the cloud-based EasyEDA for PCB design. This card XORs together the horizantal and vertical synchronization signals to form a composite. The benefits of using RGB rather than S-Video are superior contrast and clarity. To get around this, we can use the similar ADV7123 chip datasheet. This small and simple circuit allows you to connect your VGA card to your TV via SCART with the great advantages of using RGB over S-Video. Unfortunately, the GM7123C chip datasheet is only available in Chinese. To capture the schematic for the PCB design, we use the application circuit from the datasheet. ![]() However, due to the lower number of pins available to me from the 40P FPC connector, I decided to stick with the 24-bit resolution. This chip consists of three 10-bit DACs for each of the RGB lanes, providing up to 30-bit colour resolution. An R2R DAC of this size would be unwieldy, so I decided to use a GM7123C chip. ![]() | Resolution | Refresh Rate | Pixel Clock (MHz) | Display (H) | Inactive Area (H) | Display (V) | Inactive Area (V) | | - | - | - | - | - | - | - | | 640x480 | 60 | 25.175 | 640 | 160 | 480 | 120 |įor the VGA output, we use a parallel 24-bit RGB bus from the FPGA to drive a DAC. This includes an inactive area of 160x120, which consist of the Front Porch, Sync Pulse and Back Porch. It uses a slow enough clock (25.175MHz) that most FPGAs can provide, yet enough resolution for most uses. The circuit accepts a 1-volt peak-to-peak composite input, and delivers RGB and sync outputs, also with a swing of 1 volt. For my case, I was working with a 640x480 resolution, the most common VGA resolution for most use cases. ![]()
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