Tandy 1000 HX Technical Reference Manual page 399

Attributes:
Color modes:
foreground color:
bit 0 = blue
bit 1 = green
bit 2 = red
bit 3 = intensity
All bits off = black
background color:
bit 4 = blue
bit 5 = green
bit 6 = red
bit 7 = blink
All bits off = white
Scroll Down
Scroll active page down.
Entry Conditions:
AH = 7
AL = number of lines to scroll (0 means blank entire window)
CH = row of upper left corner of scroll window
CL = column of upper left corner of scroll window
DH = row of lower right corner of scroll window
DL = column of lower right corner of scroll window
BH = attribute (alpha modes) or color (graphics modes) to be
used on blank line. See Scroll Up (AH = 6) for attribute
values and Set Color Palette (AH = 11) for color values.
Read Attribute or Color/Character
Read a character and its attribute or color at the current cursor
position.
Entry Conditions:
AH = 8
BH = display page number (not used in graphics modes)