Chapter
6
I
BIOS
Services
Read
Light Pen Position
Reads light pen position.
Entry Conditions:
AH
=
4
Exit Conditions:
AH
=
0: light pen switch not activated
AH
=
1:
light pen values in registers
DH
=
row of current light pen position
DL
=
column of current light pen position
CH
=
raster line (0-199)
BX
=
pixel column (0-319 or 0-639)
Select Active Page
Select active display page (valid in alpha mode only).
Entry Conditions:
AH=5
AL
=
0
through
7:
new page value for
modes
0,
1
AL
=
0
through 3:
new page value for
modes
2,3
AL
=
80H:
read CRTICPU page registers
AL
=
81H:
set
CPU
page register to value
in
BL
AL
=
82H:
set CRT page register to value in
BH
AL
=
83H:
set both CRT and CPU page registers in
CL
and
BH
Exit Conditions:
bit
7
of
AL
=
1:
BH
=
contents of CRT page register
Scroll
Up
Scroll
active page up.
Entry Conditions:
AH
=
6
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
BL
=
contents of
CPU
page register
used on blank line
198
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