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40x25 characters on the TV? — Parallax Forums

40x25 characters on the TV?

cbmeekscbmeeks Posts: 634
edited 2006-05-28 19:50 in Propeller 1
Anyone done this (ala Commodore 64 display)?

From what I've read, it might be very difficult to do with one cog. What about 2-3 cogs?

For my project, I am seriously considering a propeller for video and a propeller for audio/IO.

So in theory, if I hade one propeller just for video, would the 320x200 resolution that Commodore 64 can output be possible? Also keep in mind I would probably need at least one cog for communicating with the rest of the system.

thanks!

cbmeeks

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Comments

  • cgraceycgracey Posts: 14,206
    edited 2006-05-23 15:58
    You could do this with just one COG, no problem. The big issue is that 320x200 pixels takes 8KB * bits/pixel. This eats memory pretty quickly. TV data rates are much lower than those of VGA, so one COG would be sufficient. You would need to make a small pixel font to match the C64's. This could all·be done.
    cbmeeks said...
    Anyone done this (ala Commodore 64 display)?

    From what I've read, it might be very difficult to do with one cog. What about 2-3 cogs?

    For my project, I am seriously considering a propeller for video and a propeller for audio/IO.

    So in theory, if I hade one propeller just for video, would the 320x200 resolution that Commodore 64 can output be possible? Also keep in mind I would probably need at least one cog for communicating with the rest of the system.

    thanks!

    cbmeeks

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    Parallax, Inc.
  • cbmeekscbmeeks Posts: 634
    edited 2006-05-23 16:15
    hmmm...let me see:

    256 characters (could probably use MUCH less) with 64 bytes per character (8x8 font) (monochrome) would equal 16k. man, that's a lot. How many actual characters would I need? Isn't ASCII like 128 characters? (which would also be 8k).

    What I was thinking would be to use 40x25 characters with 1 byte per character for the screen memory (1000 bytes). If you could pull from ROM the 8/16k character map, then wouldn't you just need the 1000 bytes of ram?

    I haven't read all the specs yet so I don't know how much ram I can play with in real-time.

    I am really shooting for Commodore 64/Atari 800 specs. So, can the propeller compete with the VIC II? [noparse]:D[/noparse]

    hehehe

    cbmeeks

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  • rokickirokicki Posts: 1,000
    edited 2006-05-23 17:08
    You only need 96 characters (or 95 or 94 depending on what you want to do with rubout and with space).
    So that's only 768 bytes of memory, not bad. It would even fit entirely in cog space.
  • cbmeekscbmeeks Posts: 634
    edited 2006-05-23 18:45
    ARGH!!

    I am such a freaking idiot. I was thinking 64 bytes per character when you only need 8 bytes per character (mono). 8 lines tall with ONE byte per line.

    So, you are correct, 96 characters would = 768 bytes. I think I would like at least some graphic chars so 128 would be cool (1k).

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  • GadgetmanGadgetman Posts: 2,436
    edited 2006-05-23 20:16
    The question you should ask yourself is 'Do I need both upper and lower case?'...

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  • cbmeekscbmeeks Posts: 634
    edited 2006-05-23 20:30
    yes, I do want them.

    In fact, I would like to steal the entire Commodore 64 character set

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  • Kaos KiddKaos Kidd Posts: 614
    edited 2006-05-23 21:22
    Why not just jack in the rom... and read...

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  • cbmeekscbmeeks Posts: 634
    edited 2006-05-23 21:46
    That's what I hope to do. I was wondering if maybe anyone has done that?

    To reproduce the Commodore 64 display (not counting multi-color graphic modes, etc), I would have to:

    1) Have it's character set in ROM
    2) Have 1000 bytes devoted to live screen data (40x25)
    3) Have 1000 bytes devoted to live color ram (foreground, background)

    So, 2000 (slightly lower then 2048) bytes for the screen should be all you need in ram. Not counting the ram it takes to process each scanline.

    I'm assuming you could just pull from ROM (via external FRAM chip??) the actual characters.

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  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-05-23 22:12
    As I recall the C=64 Character ROM was 8X8 font.· I have a "Byte" character font which I added to a ROM Chip some years ago along with the original so I select which font my 128D used.· I believe I still have that font file, but you would have to read the orginal from a Character ROM Chip, which I no longer have.

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  • cbmeekscbmeeks Posts: 634
    edited 2006-05-23 22:19
    thanks, but I could probably swipe enough of the font by hand for demo purposes.

    I hope to be able to buy the demo board this week so maybe I can just get started. smile.gif

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  • Kaos KiddKaos Kidd Posts: 614
    edited 2006-05-24 16:04
    I'll see if I'v got a C64 ROM about, and if I do, I'll let you know; it's your for the asking.

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  • ForrestForrest Posts: 1,341
    edited 2006-05-24 16:59
    An Atari 8-bit font (from the Atari 400/800, etc) should also work well - it's a 7 x7 font (that fit's nicely in a 8 x 8 cell with 1 pixel for character/line spacing).
  • Paul BakerPaul Baker Posts: 6,351
    edited 2006-05-24 17:46
    Perhaps this page can help: http://www.sxlist.com/techref/datafile/charsets.htm

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  • Ym2413aYm2413a Posts: 630
    edited 2006-05-28 19:50
    Why not just copy the fonts from this page?
    qtchicks.hp.infoseek.co.jp/fonts2.html

    You can find a lot of bitmap fonts on the internet which you could just convert over.
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