[Coco] hardware scrolling revisited...

[John W. Linville]

On Mon, Dec 02, 2013 at 04:44:31PM -0500, Arthur Flexser wrote:
> Why, then, support SG-4 (SET/RESET graphics) but not the other
> semigraphics modes?  Presumably, SG-4 would require the SAM if the
> other semigraphics modes do.

If you presume that the SAM was replaceable but the VDG was not, then
it is easy to support SG-4 since (unlike SG-8/12/24) it is inherent
to the VDG and doesn't require the SAM.  SG-8/12/24 are created by
the SAM advancing the video buffer address at a different pace than
what the VDG expects.

John
-- 
John W. Linville		Someday the world will need a hero, and you
linville at tuxdriver.com			might be all we have.  Be ready.