AVR Mega16 PAL/NTSC制式 B/W 信号模拟

资料参考

http://www.rickard.gunee.com/projects/video/pic/howto.php

http://tinyvga.com/avr-sdram-vga

http://www.serasidis.gr/circuits/colour_bar_gen/colour_bar_gen.htm

http://belogic.com/uzebox/index.asp

以下引用自 http://eyetap.org/ece385/lab5.htm

SEQUENCE:

• Horizontal sync (hsync) pulse: Start each scanline with 0.3V, then 0V for 4.7us (microseconds), and then back to 0.3V. This tells the TV to start drawing a new scanline

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• The "Back Porch": A transition region of 0.3V for 5.9us between the hsync pulse and the visible region, off the left edge of the TV

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• Visible scan region: This is the part you actually see. 0.3V shows up as black, 1V as white, everything in between is greyscale. The visible region lasts for 51.5us

• The "Front Porch": A transition region of 0.3V for 1.4us before the hsync pulse of the next line, off the right edge of the TV

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• Vertical sync (vsync) pulse: Lines 243-262 of each frame (off the bottom of the TV) start with 0.3V for 4.7us, and the rest is 0V. This tells the TV to prepare for a new frame. Think of it as just 0V with an inverted sync pulse

       代码模拟的PAL信号时序，SPI输出f_cpu/2=16Mhz/2=8Mhz.

        #include