View Full Version : do you think is it possible? vga-->prop-->displ

04-30-2008, 06:50 AM
I woke up with a wierd idea this morning...
Would it be possible to use the prop to read a VGA signal in input and use the "image" coming trhough to show it on a display?
now...let's assume low refresh rate and very few colors (2-4-16-256 probably)....

Mike Green
04-30-2008, 07:08 AM
It would be possible at a low enough resolution, low enough refresh rate, and low enough color count.· You'd need an external 3 channel high speed digitizer (flash ADC)·and an external·sync separator.· You'd need to limit the amount of data to a bitmap that would reside in hub memory with room to spare for the program.· Alternatively, you'd need a high speed external screen buffer memory.

This is one of those ideas that probably would be doable, but not really practical for anything.

Peter Jakacki
04-30-2008, 10:42 AM
Just as an idea and an academic exercise it is possible with an RC DAC + 3 comparators (quad pack 100ns). Assuming that the image is static for the moment if we synch to the vertical synch pulse and pick out the next horizontal line then we can simply read in the digital state of the comparators and accumulate those bits in the cog memory. Even 320 resolution would only be 30 longs (RGB) each time. Those longs could be synchronously written every 32 bits or buffered at the end of the line.

Unlike composite video the synch signals can be read directly or buffered with a spare comparator or two. Use the WAITPEQ/WAITPNE to synch up and then control the sample timing simply by judiciously arranging the ASM code and perhaps using a few dummy instructions to pad it out. VGA scan lines are 31.78us each which is easy enough for a cog to handle considering it doesn't have to worry about interrupts or anything else like that.

The idea is to build up a picture and refine it frame by frame by setting the RC DAC output voltage to a different level each time so that you just read in 3 bits at a time. If you were to take the output of the camera you could at least do a 8 color frame grab in the first frame and get better each time but of course there is the smearing if the input changes, so don't take too long.

Just an idea.