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VGA driver modifying — Parallax Forums

VGA driver modifying

PatMPatM Posts: 72
edited 2007-07-01 15:54 in Propeller 1
Ok, I read through both the NTSC and VGA sections of the manual and looked at the VGA demos, but I can't figure out how to modify the vga driver to use a different resolution.

The manual explains a 640x480 display, telling you all the time periods needed for the porches etc. I look at the demos and there are numbers that bear no resemblance to those time periods or even to the other vga demos. Obviously, the time periods are not fixed to those shown for 640x480 example.

How do I determine how many ticks to allocate to each portion of the signal?

What I'd like to do is get a vga driver to show 320x240, 320x200, and 240x128 for use with LCD panels but I haven't rigged one up for use with the Hydra yet and I'm not even sure my monitor can show resolutions that small! However, if I can find out the magic behind calculating ticks, it shouldn't be a problem.
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Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2007-06-30 19:42
    There is one driver that has 3 different resolutions (640x480, 800x600, 1024x768). At the beginning of the driver, there are 3 sets of comments, one for each resolution. 2 of the 3 are "commented out" while one is active. You can see the active one has "'{" on the first line and "'}" on the last line. That'll give you some idea of how the values change with resolution. There is a VGA driver (VGA.spin) that already is available (look in the Propeller Tool's library) that uses 320x240 for compatibility with the TV driver.
  • PatMPatM Posts: 72
    edited 2007-07-01 12:00
    I'm getting closer to getting the video mode I want - its just taking a while to understand the signals. For instance, the one driver says it uses timing for 1024x768 with lower resolution. I think I understand what they're talking about finally.

    I still haven't found a demo that runs at 320x240 though...
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  • Mike GreenMike Green Posts: 23,101
    edited 2007-07-01 12:25
    I looked again at the driver (VGA.spin). It's set up for 512 x 384. At the end of the source file, there's a large section of comments which explains the various parameters and it looks like they could be changed to get the lower resolutions, but I haven't tried any of them (partly because I don't have a monitor that would accept it).
  • PatMPatM Posts: 72
    edited 2007-07-01 14:14
    Well, I got the 320x240 working with vga.spin earlier. Works nice, but the rom font is way too big.

    So then I looked at the hires text driver and got that down to 320x240 and the font size is perfect. Only problem·is that its·2 colours (understandable since the goal was hi-res). I've been trying to figure out how to change to 4 colour mode but my head is hurting too much at the moment lol.

    I didn't really expect to have to do quite this much work to get video working at lower resolutions. But I guess the Prop is being targetted at the TV games crowd and VGA isn't getting the same amount of attention. Oh well, gotta go where the market wants!

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  • Mike GreenMike Green Posts: 23,101
    edited 2007-07-01 15:54
    You have to remember that the TV.spin and VGA.spin drivers were written by Chip to support the development of the Propeller and the Demo Board and intended for a basic display environment ... NTSC/PAL for TV and a cheap generic computer display for VGA. Later he wrote the higher resolution drivers, mostly as a demonstration of the capabilities of the Propeller since it wasn't at all clear that the Propeller could handle the high bit rates involved or how it could be done. Parallax has very limited programming resources. A lot of stuff is done by the customers in response to their own needs and contributed back to the "community" for everyone's benefit. You should consider starting your own thread, posting what you've done, and asking if others could make suggestions or help with improvements like changing to 4 colour mode.
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