potatohead's Blog - 40, 64 and 80 Column Text Driver for Propeller

RSS Bot · September 28, 2009

I got stuck on this and it took way longer then I thought. Got it done though! 80 characters in color on composite video is a big stretch. Only some color combinations work well, but there is the S-video option. When I get my next capture device in, I'm going to run the S-video and check it out. Hoping it looks really good.

Eric Ball did a very nice starter Propeller video signal template. I have struggled and continue to struggle with getting the signal characteristcs I want, but there is more progress than not, so I'm feeling good about that.

This driver has an 80x25 text display memory, uses an Atari font in RAM, and has a word per character for color definition. All in all, a nice memory foot print for this kind of thing, and lots of color choices. Was going to go with just a byte and use a palette, but doing that kind of thing is a lot more expensive than I realized. So, the lesson learned on Propeller is don't go for color indirection. It's too slow for useful resolutions, or takes too many COGs. One or the other will occur. (unless I'm missing something, who knows?)

The cool thing about this driver is that most of the functions are live and can be changed after the driver is launched. Acts just like a graphics chip does and that's just fun. There are a few more things to add to the live functionality, but no worries there. Easy to do.

Display modes are 16, 32, 40, 64 and 80 x 25 text display, with 256 character re-definable font in RAM. Signal characteristics are:

"Scan Doubled" interlaced 200 line vertical display. This really helps with clarity on the color. It was surprising to me how much impact doing this had.

Non-interlaced 200 line display.

Color burst on, or off for getting the most out of a display device. If you don't need color, or maybe just need intensities, this is the way to go.

Two color per screen mode for speed and smaller run time memory foot print.

This project is winding down, meaning I can get back to my Harmony setup and continue some work on the VCS!

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