Tandy 1000 Programmer's Reference Guide

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.
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Tandy 1000 Specifications

General

Processor	Intel 8088
Processor Speed	4.77 MHz
RAM	128 KB (expandable to 640 KB)
Operating System	MS-DOS 2.11
Manufacturer	Tandy Corporation
Release Year	1984
Storage	Single or double 5.25" floppy disk drive (360 KB), optional hard drive
Sound	Tandy 3-voice sound
Ports	Parallel, Serial
Graphics	CGA (Color Graphics Adapter)
Graphics Modes	320x200, 640x200