eslapion wrote:Its not such an easy mod but the results are stunning!
The ability (finally!) to have the 3K ram expansion area with the VIC's internal AND 8K BLK ram expasion areas all contiguous is just plain lovely.
Now, could we use such a mod to have interlaced display on the VIC as well? (double the vertical resolution)
I remember there had been some controversy in the forum, as to whether interlace on the 6560 really works as expected.
In principle, that would require flipping two different screens every 1/60 second and properly discerning even and odd frames. If the latter point is not adhered to, even and odd lines in the picture are swapped, distorting the display.
The address generator would consist of two text screens at $0400 and $1200, pointing to the two different bitmaps, each one of them using half of remaining memory like this:
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$0400 .. $04D1 - text screen 1 for odd field
$04E0 .. $11FF - odd field bitmap
$1200 .. $12D1 - text screen 2 for even field
$12E0 .. $1FFF - even field bitmap
... which would yield a 168 x 320i resolution. This one can also be done as FLI variant.
Could you make a modded kernal that would automatically recognise all 3 memory areas to provide for a VIC with about 31k of BASIC ram?
If the kernal can savely assume, that internal RAM has been expanded, this just requires two changes in RAMTAS:
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.FDD2 A9 06 LDA #$06 ; had been LDA #$12
.FDD4 8D 82 02 STA $0282
.FDD7 A9 04 LDA #$04 ; had been LDA #$10
.FDD9 8D 88 02 STA $0288
Without an external RAM expansion, screen memory remains at $1E00 and BASIC starts at $0400. Those four instructions shown above move down screen to $1000 and BASIC start to $1200 on an unpatched kernal - and the patch alters these addresses to $0400 and $0600, respectively.
OTOH, this could lead to increased incompatibility, as a lot of programs which require 8K or more depend on the BASIC start being at $1200 - so for me the solution with 'max.prg' seems to be an easier way to get the same result.