VGA视频信号详解_maik分析.doc

VGA视频信号详解 最近做了一些关于视频的工作，稍微研究了一下V4L2和硬件上的视频知识，其中包括了VGA、component、PAL等信号。在这里总结一下关于VGA信号波形方面的知识。 在学习VGA的视频输出的时候，很容易就可以从网上找到相关的引脚定义： 1 红色视频信号(Red, 75 ohm, 0.7 V p-p) 2?绿色视频信号(Green, 75 ohm, 0.7 V p-p) 3?蓝色视频信号(Blue, 75 ohm, 0.7 V p-p) 4显示器标识信号#2(Monitor ID Bit 2) 5地线(Gnd) 6红色视频信号地线(Red Gnd)7绿色视频信号地线(Green Gnd)8蓝色视频信号地线(Blue Gnd)9未连接(No Pin)10?同步信号地线(Sync Gnd) 11?显示器标识信号#0(Monitor ID Bit 0)12?显示器标识信号#1/SDA(Monitor ID Bit 1 or SDA)13??水平／复合同步信号(Horizontal Sync or Composite Sync)14??垂直同步信号(Vertical Sync)15??显示器标识信号#3/SCL(Monitor ID Bit 3 or SCL) Introduction VGA is a high-resolution video standard used mostly for computer monitors, where ability to transmit a sharp, detailed image is essential. VGA uses separate wires to transmit the three color component signals and vertical and horizontal synchronization signals. VGA Signals Like any video format, VGA video is a stream of frames: each frame is made up of a series of horizontal lines, and each line is made up of a series of pixels. The lines in each frame are transmitted in order from top to bottom (VGA is not interlaced), and the pixels in each line are transmitted from left to right. Separate horizontal and vertical synchronization signals are used to define the ends of each line and frame. A composite synchronization signal (actually an XOR of the horizontal and vertical signals) is also encoded on the green color channel. The ADV7125 video DAC reads an 8-bit value for each of the red, green, and blue channels on each cycle of the pixel clock. There is a two-cycle pipeline delay between when the digital codes are read by the DAC and when the corresponding analog voltages appear on the DAC outputs. The RGB input signals can be overridden by the sync and blank signals: The active low blank signal forces all three DAC outputs to their black level, while the active low sync signal forces the green DAC to a special sync level below the normal black level. Each line of video begins with an active video region