320x400x256 mode

 BBS: Inland Empire Archive
Date: 11-11-92 (12:47)             Number: 397
From: EARL MONTGOMERY              Refer#: NONE
  To: ALL                           Recvd: NO  
Subj: 320x400x256 mode               Conf: (2) Quik_Bas
I ran across this text file that claims to explain how to
get into this mode. I know the CRTC and Sequencer port
addresses but I have no idea what index registers are. If
this ASM language? Anyway I've noticed some interest in the
above and thought I would pass the text file on for those
that are interested. If anyone comes up with a way to get
this mode from QB without using a library please post!
To change from the MCGA Video Mode 13 Hex (320x200x256) to the Secret Video
Mode (320x400x256). Set the video mode to 13 Hex and then change the following
registers. To change back to 320x200x256, just restore the changed registers.


        Index  9  From 41  To 40     Index  4  From 0E  To 06
        Index 20  From 40  To 00
        Index 23  From A3  To E3

To address the new mode (320x400x256) you must use the Sequencer Write Plane
Mask register (index 2) to control which video plane you are writting to.
The screen pixels are addressed from the top left corner. The first screen
pixel is in Plane 0 - byte 0, the second pixel is in Plane 1 - byte 0, the
third pixel is in Plane 2 - byte 0, the fourth pixel is Plane 3 - byte 0.
Repeat this sequence for all 128,000 pixels. This mode uses the first 32,000
bytes of memory from each of the four video planes.

                         320x400x256 Mode

                         P P P P P P P P
                         i i i i i i i i
                         x x x x x x x x
                         e e e e e e e e
                         l l l l l l l l

                         0 1 2 3 4 5 6 7

                         P P P P P P P P
                         l l l l l l l l
                         a a a a a a a a
                         n n n n n n n n
                         e e e e e e e e

                         0 1 2 3 0 1 2 3

                         B B B B B B B B
                         y y y y y y y y
                         t t t t t t t t
                         e e e e e e e e

                         0 0 0 0 1 1 1 1

Please excuse the format!

--- Maximus 2.01wb
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