luke@mnetor.UUCP (Luke Matthys) (10/22/87)
Does the PS/2 VGA support the notion of multiple video pages and if so,
how does it handle the second 150K page (640x480 with 16 colors) when all
it has is 256K of video memory? Is the video memory expandable?
--
Luke G. Matthys
UUCP: {decvax|allegra|ihnp4|linus|utcsri}!utzoo!mnetor!luke
BELL: (416) 475-8980 ext. 332mcdonald@uxe.cso.uiuc.edu (10/27/87)
The VGA will swap pages when the EGA will, that is in modes 0 through 3, 7, 0d, 0e, 0f, and 010h. According to the IBM Personal System/2 Seminar Proceedings Vol 5 #4, page 17 video mode table, mode 012H, the 480x640 16 color mode, has only 1 video page. Thus page swapping won't work. This source makes no reference to extensibility other than the very expensive one with both higher resolution an larger color palete. Doug McDonald
ks26+@andrew.cmu.edu (Kenneth Sykes) (10/29/87)
While VGA mode 12h (640x480x16) does not support page switching, there is more than 480 lines worth of screen memory. The 640x480 buffer uses 80x480 bytes of memory (approx. 38000 bytes). The remaining 26000 bytes or so in the 64K segment is valid screen memory. I've used this to save and restore screens quickly (along with write mode 1). The one caveat I've found so far is the Microsoft mouse seems to trash/use the memory immediately below scan line 480, so I use the memory starting at scan line 500, which seems to work. Fine.