Guest essele Posted September 25, 2011 Report Share Posted September 25, 2011 Hi, I'm new to this forum, and pretty new to FPGA's and Papilio, but having immense fun experimenting ... so forgive the potentially silly questions. Anyway, I've been experimenting with an FPGA project on the Papilio One, using VGA as output, I need more colours than the standard wing, so I put together a PCB thats 4-bit per colour. It's only an experiment, and I was also testing out a low cost PCB fab, so apologies for pinching the logo ... I just wanted to see how it would come out :-[ )... Anyway, once I got the board populated (don't laugh at my soldering) and plugged in I wasn't getting quite what I expected on the screen. I put together a simple module (hmmm, not sure what the right terminology is here) that generates VGA timing and then uses a few bits of the horizontal position to control the 4 bits of the red output. (Sorry about the awful picture) As you can see from the picture about half of the bands are missing, I presume these are the darker ones. My initial thought was that I had either messed up my PCB or mis-soldered. However a scope trace shows a pretty good output. So, from the trace I would assume that everything is working ... so then I suspected the monitor, on a different one I got a slightly better result (one or two more bands) but still not perfect. So my gut feel here is that most of the lower half of the voltage range is ignored by the monitor. All the specs I've found suggest 0v = black and 0.7v is full colour, but at least 0.2v is still black from what I can see. Is that right? Normal? Should I be designing to use 16 steps from 0.2 to 0.7v or am I just being paranoid? My ultimate design target is digitally connected LCD, so this isn't going to be a problem long term, but I do tend to get distracted by these kind of things! Any help greatfully appreciated. And if anyone wants the pcb layout or schematics then I can post them (not that there's anything complicated in them.) Thanks, Lee. Link to comment Share on other sites More sharing options...
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