mirror of
git://projects.qi-hardware.com/ben-blinkenlights.git
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67 lines
2.3 KiB
HTML
67 lines
2.3 KiB
HTML
<HTML>
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<TITLE>
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UBB-VGA
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</TITLE>
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<BODY>
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<H1>UBB-VGA</H1>
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This is an effort led by Werner Almesberger to use the
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<A href="http://en.qi-hardware.com/wiki/UBB">UBB</A>
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(Universal Breakout Board), a few resistors, and a VGA cable to create a
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workable VGA signal on the
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<A href="http://en.qi-hardware.com/wiki/Ben_NanoNote">Ben Nanonote</A>.
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<H2>What it can do</H2>
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The video signal timing is controlled by software. Available resolutions
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include 640x480 and 800x600.
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At present, the maximum resolution is 1024x768 with a refresh rate of 50 Hz:
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<P>
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<A href="ubb-vga-pub-1024.jpg"><IMG src="ubb-vga-pub-1024-small.jpg"></A>
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<P>
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The 16 colors are generated from a binary channel for red, green, and blue
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each, plus a binary luminance channel that affects all colors.
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<H2>The hardware</H2>
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The current design is based on the
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<A href="http://en.qi-hardware.com/wiki/UBB">Universal Breakout Board</A> (UBB)
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that plugs into the Ben's
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<A href="http://lists.en.qi-hardware.com/pipermail/discussion/2011-January/006908.html">8:10 card</A>
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slot. The MMC controller in the Ben's Jz4720 CPU is tricked into
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considering the UBB-VGA board as a MMC/SD device and streaming the pixel
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data at a rate of up to 56 MHz.
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<P>
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The pictures below show a prototype that connects directly to a VGA cable:
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</P>
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<A href="ubb-vga-pub-plugged.jpg"><IMG src="ubb-vga-pub-plugged-small.jpg"></A>
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<A href="ubb-vga-pub-v2.jpg"><IMG src="ubb-vga-pub-v2-small.jpg"></A>
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<P>
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The circuit is very simple. In its most basic form, it consists of UBB,
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ten resistors, and the VGA cable:
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<P>
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<A href="ubb-vga-schem.png"><IMG src="ubb-vga-schem-small.png"></A>
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<P>
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Each of the three analog color channels uses three resistors for lowering
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the 3.3 V logic voltage to the 0.7 V analog VGA level and for mixing in the
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luminance (Y) signal. The tenth resistor pulls down the HSYNC/CMD
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line, to fake the "not busy" signal the MMC controller expects to receive
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from a MMC device when starting a block write.
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<H2>The software</H2>
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The driver currently runs in user space (with a lot of dirty tricks) and
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blocks all other system activity while running.
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It can display the test image shown above, the content of the LCD display,
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or a PNM image.
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The source code can be found
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<A href="http://projects.qi-hardware.com/index.php/p/ben-blinkenlights/source/tree/master/ubb-vga">here</A>.
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</BODY>
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</HTML>
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