Timeline for Can a Commodore 64 use two screen modes on one scanline?
Current License: CC BY-SA 4.0
8 events
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| Nov 12, 2021 at 20:42 | comment | added | supercat | I wonder how hard it would have been for the VIC-II to support modes without badlines--either assuming a constant value read from character memory, or blanking every eighth row but repurposing what would be shape data fetches for character fetches? Having every eighth scan line blanked would have been less annoying than having to blank the entire screen. | |
| Aug 16, 2020 at 22:05 | comment | added | DisplayName | That is a really interesting find! I've coded quite a bit on the C64, but never knew the VIC had this hidden screen-mode which is a mix of text-mode and bitmap-mode. Granted it's hard to exploit, since it's only there for 2 cycles per $D011-write. And the screen-mode itself isn't too flexible, since the screen-bytes both decides the character to show as well as its foreground + background color (each char is locked to a specific fg and bg color). But still, it might be useful for something - it's like an extended "extended color mode" (256 chars instead of 64 and 16 bg colors instead of 4). | |
| Jan 20, 2019 at 22:28 | vote | accept | Omar and Lorraine | ||
| Jan 15, 2019 at 20:37 | comment | added | Maury Markowitz | Unless I'm mistaken, the only system of that era I knew that had official support for this sort of thing was the Nutting chip that was used in some of the Midway arcade games.IIRC it had a register based on the color clock that switched to/from text mode. Gorf used this maybe? I'd love to know if there were other examples that deliberately included this feature. | |
| Jan 15, 2019 at 5:27 | comment | added | Janka | @Tommy: $3fff in VIC 14-bit addressing. The actual byte read may be at $3fff, $7fff, $bfff or $ffff (always RAM), depending on the VIC page selected by CIA2. | |
| Jan 14, 2019 at 19:55 | comment | added | Tommy | You can prevent badlines by constantly tweaking the y scroll register so that the Vic never finds itself to have reached the first line of a new character row. Unfortunately I think it will just revert to its in-visible-area idle state of fetching and outputting the value at 3FFF on a black background once it runs past where it should have had a bad line, so I don't immediately have a means to make that observation especially helpful. | |
| Jan 14, 2019 at 11:32 | history | edited | Peter B. | CC BY-SA 4.0 | added summary plus alternative non-raster solution |
| Jan 13, 2019 at 21:01 | history | answered | Peter B. | CC BY-SA 4.0 |