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This can be done with the Propeller 2 — Parallax Forums

This can be done with the Propeller 2

Comments

  • plainsteveplainsteve Posts: 33
    edited 2011-06-28 20:16
    It could also be done with a 6502.
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2011-06-28 20:33
    It can also be done on the prop I, albeit at lower resolution http://www.youtube.com/watch?v=qVb8d7ls8Tg

    Actually, thinking about the resolution, is there any reason the resolution can't be increased for TV? That demo is 3 pins, one cog and 12k of hub ram. Any reason one could not use more pins, 24k of hub ram and two cogs to give a D to A with more resolution, and hence (?) more colors?
  • potatoheadpotatohead Posts: 10,261
    edited 2011-06-28 21:22
    None at all. Baggers did 24 bit, 120xsomething with a DAC, and a fair number of pins. Three TV circuits, 3 pins each, could also do component for a fairly nice color set, given a display that can take component.
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2011-06-28 22:06
    None at all. Baggers did 24 bit, 120xsomething with a DAC, and a fair number of pins.

    Intriguing. I know it isn't 1080, but even 16 bits ought to give a lot more colors than 8 bits. I tried searching on the forum for this - you wouldn't happen to have a link by any chance?
  • BaggersBaggers Posts: 3,019
    edited 2011-06-29 02:06
    Prop24.jpg

    http://forums.parallax.com/archive/index.php/t-95706.html
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2011-06-29 03:41
    Whoa! I see a lot of colors.

    Ok, strange deja-vu feeling reading that thread link - same questions, same answers.

    Playing around with the video on these small TV screens, I am thinking that more colors is going to improve the picture better than more pixels. 128x96 is only just on the 'blocky' size on a 4" display. (Very different to a VGA display where it is seriously 'blocky').

    These displays are all "yellow RCA", ie NTSC or PAL - autoselect inside the display. I am finding that PAL does colors slightly better, but there is a lot of shimmering of the display, whereas NTSC is much more solid looking.

    So looking back at some of the comments on that thread re all the different formats around the world, if it is ok maybe we just look at NTSC via RCA for the moment, so if we use that, and look at 2 bytes per pixel = 24k for 128x96, and as many resistors as you may need, and as many cogs as you may need, do you think we can improve the color resolution? It would be cool to be able to play my skiing videos at something better than this resolution http://www.youtube.com/watch?v=HyJLB4m1D_o
  • potatoheadpotatohead Posts: 10,261
    edited 2011-06-29 09:43
    Yes, PAL colors do look a bit better to me here as well, but... The tolerances on the color references for PAL are tighter than those necessary for NTSC. Also, the complexity for PAL is higher overall. Props do not output very good PAL signals. Some fiddling for a given xtal can improve that, but it's hit 'n miss. Almost all of the PAL output I've worked with was just kind of crappy. :(

    NTSC can also run with a very simple, non phase shifted color reference, which looks rock solid. Artifact tricks are possible on NTSC because of that too.

    Frankly, some of us are stuck with PAL only devices, and that's tough because it limits the driver options. I've settled on NTSC because my displays are all NTSC, with my only PAL option being the PC capture card I use most of the time, and for the much simpler and robust output from the Prop. Not everybody will be happy with that, and understandably so. IMHO, there isn't a one size fits all. Major bummer in TV land.

    The big limitation on TV color, using the Prop and resistors, is the phase shifting needed to get the different hues. More resistors will give you more shades of a given hue, but not more hues. Eric did a software color driver that does the phase shifting itself, not using the Propeller for it, for more hues, and some saturation control. That one operates at 228 pixels, but those could be doubled up horizontally and vertically for a very nice 118 x 100 pixel display.

    More resistors on that driver would yield a nice set of colors and saturation options, though it would be limited to 8 bits of color max. One could pick those colors well though. Lots of work to get there.

    Another alternative is to use a video converter chip, or drive the display component video style. The video converter chips will take RGB input, and output nice NTSC and PAL. Coley used these on a board or two.
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