Tandy 1000 Programmer's Reference Manual page 198

Chawter 6
I
BIOS Services
Function Descriptions:
Set CRT Mode
Entry Conditions:
AH
=
0
AL
=
mode value, as follows:
Alpha Modes
AL
=
0: 40x25 black and white
AL
=
1: 40x25 color
AL
=
2: 80x25 black and white
AL
=
3: 80x25 color
AL
=
4: 320x200 color graphics
AL
=
5: 320x200 black and white graphics with 4
AL
=
6: 640x200 black and white graphics with 2
AL
=
7: Reserved
AL
=
8: 160x200 color graphics with 16 colors
AL
=
9: 320x200 color graphics with 16 colors
AL
=
A: 640x200 color graphics with 4 colors
Note: If the high order bit of the AL register is 1
Graphics Modes
shades
shades
Additional Modes
then the video buffer is not cleared.
196