HP Vectra Reference Manual page 110

Mode Control Register
The mode control register is a 6-bit write-only register.
,.
Bit Data Definition
0 0 40 character alpha, 320x2 graphics, 640x1 graphics
1 80 character alpha, 640x2 graphics
0 Alpha mode
1 Graphics mode
2*
0 Color mode
1 Black and white mode
3 0 Disable video
1 Enable video
4 0 Select 320 pixel graphics
1
Select 640 pixel graphics
".
5 0 Attribute bit 7 is background intensity
1 Attribute bit 7 is blink
*Bit 2 provides a secondary function tying the blue and green
guns together changing the displayed colors.
Multi-Mode Video Adapter Card 93