how to work with foreground background videoram in 2bpp (4 colors) each ?

this is a beginner question.
I want to emulate an old game on the prop and I want to know how can I manage to
put out 2 videorams (planes) one on antoher on the prop1

As I understand I can have 4 colors per 32bit Longword on the prop.

My game has a videoram1 at $0400, a videoram2 at $0800 and a
colormap at $0c00 (3 bits for vram1 choose the palette colors, and 3 bit choose the colors for vram2)

a Pixel can have 4 colors, 00=background or nothing, 01-03 are the colors out of a palette of 8 possible colors per vram(plane) in my game.

I´m confuze how can I do this on the prop.
Has some of you an idea ?



  • I think you might need to explain what you want a bit more precisely - how is the data you need to display laid out? If it's some existing thing you want to emulate, tell us it's name.
  • vulgus from snk

    i will give an better explanation:

    everyone know how to lookup a character from videoram and fetch the graphix pixel from a charset in Ram and put this on the
    prop TV screen.
    what if I have two videorams layered togheter (for parallax srolling or characters over background image etc..)
    its easy to see that I might have more than 4 colors per 16 pixel (llongword) as we do in the propeller tv object
    how I can accomplish this on Propeller ?

    for example I show a character (8x8) with 4 colors deep (2bpp) and overlap this partially with an second charachter (8x8) with
    different 4 colors ?

  • sorry typo - not vulgus it should read: Vanguard
  • Ahhh, in this case, it is best to use "high color" mode - the VCFG is configured to 4-color mode, but VSCL is set for 4 pixels per WAITVID. Now, if given the pixels %%3210, what is usually the palette becomes 4 8bpp pixels.

    If you want a reasonably-well commented, maybe slightly over-complicated example/template of efficient graphics in that manner, take a look at my JET-Engine, whose forum thread I have linked in my signature. It sets up 4 cogs to render single scanlines into a 256x8 buffer, which are then sent to the TV by another cog.
  • Thank you Würfel. 4 cogs wow. I hope I´m not running out of cogs in my emulation....
    (need a lot cogs now for adressbus intercepts(external SRAM), sound emulation, debug , 6502cpu core, etc..)

  • your jet Engine is AWESOME ! Congrats I´m impressed.
    what I can modify to run Jet Engine on an RGB /sync CRT ?
    I assume to switch to vga mode with 15Khz Vblank clk ?
  • I actually have a 31KHz VGA version laying around unreleased. Still has some issues to work out.

    However, if you're using the standard 64 color RGB circuit, you should be able to easily adapt the composite output module to RGB by simply changing the VCFG mode, pin assignment and the sync colors. I've attached a version of the demo program with RGB colors, if that helps you.
  • thank you a lot !!!!!!! I check this out. Great Work.
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