VGA object examples

Mike Green

There seem to be several examples of the use of the TV object, but I can't find any examples of the use of the VGA object. Are there some examples hiding somewhere that I've missed?

cgracey

Mike,

You're right - there's nothing yet. I'm working on a set of teminals, one for TV and one for VGA, which will use the Propeller's built-in font. These will use only one extra COG and require less than 3KB of RAM. I hope to have these posted early next week. They will work much like tv_terminal, but be smaller, lower-memory, and WAY faster because they're dealing with character memory, not a full-blown bitmap.

VGA was pretty fun to play with during the development of the Propeller because you could make all kinds of custom modes which could maximize the chip's capability without having to conform to specific display modes. Interlacing was really nice, too. All this development was done using CRT's. Well, now that it's 2006 and CRT's are nearly history, LCD's are the norm. LCD's are great because of their small size and lower power, but it turns out they have very narrow ranges of display modes. They won't widely auto-sync and interlace (at all)·like the old CRT's did. Instead you have to follow standard timing recipes.·So, I will make the VGA terminal·object output in some·well-known mode, like·640x480 @ 60Hz, but because the Propeller can't pump out pixels at 25MHz (tops out at 20MHz w/80MHz clock), I will have about 20% fewer pixels on·the display line to fit it into 20MHz. This will yield 32x15 characters, and every LCD can lock to this.

Mike Green said...
There seem to be several examples of the use of the TV object, but I can't find any examples of the use of the VGA object. Are there some examples hiding somewhere that I've missed?

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Chip Gracey
Parallax, Inc.

Post Edited (Chip Gracey (Parallax)) : 5/14/2006 7:00:04 AM GMT

Jim C

Chip:

Thanks for the info about VGA screens. I've been trying to decypher VGA_Demo.spin and VGA.spin, and it is pretty confusing. The discussion of a 32x15 limit makes sense.

I am also interested in using the bit-map approach with a VGA. Is there an easy way of working with the Graphics.spin driver with a VGA_Demo kind of program?

Jim C

Paul Baker

The 32x15 is refering to the tile structure of the VGA driver, I believe the tiles are organized into 16x32 in conformity with the stored font. This would correspond to a resolution of 512x480 or 245,760 pixels. Since the availible memory is 32K you can see that a bitmaped VGA is not possible at that resolution (well monochrome vga would barely be possible, requiring 30,720 bytes),

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1+1=10

cgracey

Yes, graphics.spin is meant to be used not just for TV, but for VGA, custom LCDs, etc. If you are adventurous, you could adapt graphics_demo.spin to work with the vga.spin object instead of the tv.spin object. I will try to get something like this working by the end of the week.

Jim C said...
Chip:

Thanks for the info about VGA screens. I've been trying to decypher VGA_Demo.spin and VGA.spin, and it is pretty confusing. The discussion of a 32x15 limit makes sense.

I am also interested in using the bit-map approach with a VGA. Is there an easy way of working with the Graphics.spin driver with a VGA_Demo kind of program?

Jim C

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Chip Gracey
Parallax, Inc.

Jamesx

Chip:

Looking forward to a graphic.spin for VGA. I've been trying to figure out how the TV and VGA drivers work, and I'm gradually picking away at it. But, I could sure use some help. It's easier to dissect a working version than create one!



Jim C

Mike Green

Chip, thanks for the information. I look forward to the additional examples and the arrival of a Propellor Demo Board to try them on this coming week. Mike Green