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4bpp driver available? — Parallax Forums

4bpp driver available?

ProptestProptest Posts: 10
in Propeller 1
Has anyone mechanized a 4bit-per-pixel driver with arbitrary (well, the usual 96-color) pick-from-palette? I found the NTSC4x driver by Eric Ball, but it looks like the palette is somewhat fixed. I have seen how the DMA hardware supports 1bpp and 2bpp, and that other driver (also by E. Ball) that uses 2bpp and varies the color field to obtain 8bpp. I'm trying to obtain a tinted grayscale image capability (actually, greenscale, to emulate a cathode ray oscilloscope display). 4bits per pixel would give me as many gray levels as I can get from the 3-bit resistor DAC and a few more colors for display background and miscellaneous markup.



Comments

  • PropellerGuyPropellerGuy Posts: 33
    Hmmm, can you switch to VGA and use the 160x120 6-bit driver?
  • potatoheadpotatohead Posts: 10,261
    4bpp is expensive. Takes a color lookup to do.

    Jim Bagley made one, but it was moderate resolution. 128 pixels or so horizontal.

  • ProptestProptest Posts: 10
    Well then, maybe I'll improve my mind on wanting 4bpp.

    Now, Eric's 8bpp and the basic 2bpp driver are easy enough to work with so far. Are there any pre-built examples using 1bpp ?
  • ProptestProptest Posts: 10
    This seems to be 2-color howto for TV: 80 Column Color 8x8 NTSC Text Driver
  • potatoheadpotatohead Posts: 10,261
    I'm not sure we did all that many 2 color drivers.

    Any of them can be modified fairly quickly though. All that is needed is to adjust the number of waitvids per line / tile, or whatever to account for double the number of pixels per byte. All else stays the same, VSCL, etc...

    The other thing that will need to be done is to switch from 4 color to 2 color for the graphics area, and back to 4 color for the sync / signal area.

    I think TV.spin has a 2 color option as well.

    I did the 80 column 2 color driver. It's complicated, due to the effort needed to get character attributes, but the 2 color code in that makes sense.

    If the OP has a target driver, maybe it's not too tough to suggest some modifications to it.

  • ProptestProptest Posts: 10
    If TV.spin can do 2 color, i suppose that'd be great! Regarding VGA, Ive been using the 7" backup monitors as displays and they seem both cheap and good, but only take ntsc or pal.
  • RoadsterRoadster Posts: 209
    Here is 4 bit vga graphic engine, with a little work it can be converted to tv
    http://propellerpowered.com/forum/index.php?topic=415.0
  • BaggersBaggers Posts: 3,019
    I did a CPC style display driver a while back for Prop, that OBC wanted, it used a couple of cogs IIRC to drive it, as he wanted sprites also, if this is ok, I'll look into digging it out tonight.
  • BaggersBaggers Posts: 3,019
    It should be in the forums somewhere, assuming it carried across from the old forums.
  • ProptestProptest Posts: 10
    Please, don't trouble with that, I've been studying Potatohead's PotatoText scan line driver and the NTSC Templates that Eric Ball Wrote. I'll get it or come back with better questions if it goes poorly. Thanks all!
  • BaggersBaggers Posts: 3,019
    Ok, no worries :D good luck!
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