利用示波器显示VGA图像
我向来对VGA、视频信号很头疼，所以这篇文章看的晕晕乎乎，连一个摘要性的介绍都写不出。不浪费脑细胞硬抠了，做个记号先，日后用得上的时候，再回头来细细研究。
直接上原理图：
摘录部分原文：
VGA, unlike composite video, already has the two sync signals separated from the RGB (Red, Green, Blue) video signals. Simply, we take the RGB video and convert it for the Z-axis, and the sync signals to trigger the sweep signals to feed into the X and Y axes of the oscilloscope.
The sync signals generate pulses, which is used to trigger two sweep "sawtooth" generators. Two 555 timers were used for the sweep generators, which generates ramp signals so the oscilloscope can create a raster (scanning pattern). The vertical generator creates ramp signals at around 75Hz, and is tuned to the vertical sync pulses. The horizontal generator creates ramp signals at around 35kHz, and is tuned to the horizontal sync pulses. However, some oscilloscopes do not have built-in inverters, so I added an inverter on the output of the two ramp generators, and you are given the choice to invert or not invert the sweep signals (ramp or sawtooth). The 1458 OP AMP IC is used to buffer and invert (optional) the vertical sweep, and the output is fed into the Y-axis. The TL082 OP AMP IC is used to buffer and invert (optional) the horizontal sweep, and the output is fed into the X-axis.
NOTE: The sweep generators were built for my PC''''s VGA specifications, which I believe is 800 x 600 at 75Hz refresh rate. Different configurations most likely could mess up the sweep. If you wish to build this circuit on a different VGA configuration, then you may have to change "play with" the 3.9K resistor and the 220pF capacitor on the horizontal generator and the 120K and .01uF capacitor on the vertical generator.
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