3D8h (W): Mode Control register
bit 0 80x25 Alpha mode if set, 40x25 else
1 Graphics mode if set, alpha else.
2 BW mode if set, color else
3 Enable video signal if set
4 640x200 Graphics mode if set, 320x200 else
5 if set bit 7 of the attribute controls background, else blink
3D9h (W): Color Select register
The function of this register depends on the active mode.
Text modes: 320x200 modes: 640x200 mode:
0 Blue border Blue background Blue foreground
1 Green border Green background Green foreground
2 Red border Red background Red foreground
3 Bright border Bright background Bright foreground
4 Backgr. color Alt. intens. colors
5 No func. Selects palette
Palette 0 is Green, red and brown,
palette 1 is Cyan, magenta and white.
3DAh (R): Status register
bit 0 If set retrace active and the video memory may be
accessed by the PC.
1 Lightpen trigger has occurred if set
2 Lightpen switch is off if set
3 Vertical retrace active if set.
Video RAM can be accessed for the next 1.25 ms.
Video Modes:
00h T 40 25 2 (8x8)
01h T 40 25 2 (8x8)
02h T 80 25 16 (8x8)
03h T 80 25 16 (8x8)
04h G 320 200 4
05h G 320 200 4
06h G 640 200 2
