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CRT Controller Registers
Name
Port
Index
Address Register
3?4
-
Horizontal Total
3?5
00
Horizontal Display End
3?5
01
Start Horizontal Blank
3?5
02
End Horizontal Blank
3?5
03
Start Horizontal Retrace
3?5
04
End Horizontal Retrace
3?5
05
Vertical Total
3?5
06
Overflow
3?5
07
Preset Row Scan
3?5
08
Max Scan Line
3?5
09
Cursor Start
3?5
OA
Cursor End
3?5
OB
Start Address High
3?5
OC
Start Address Low
3?5
00
Cursor Location High
3?5
OE
Cursor Location Low
3?5
OF
Vertical Retrace Start
3?5
10
Light Pen High
3?5
10
Vertical Retrace End
3?5
11
Light Pen Low
3?5
11
Vertical Display End
3?5
12
Offset
3?5
13
Underline Location
3?5
14
Start Vertical Blank
3?5
15
End Vertical Blank
3?5
16
Mode Control
3?5
17
Line Compare
3?5
18
?
=
B in Monochrome Modes and 0 in Color Modes
CRT Controller Address Register
The Address register is a pointer register located at hex 3B4 or
hex 3D4.
If
an IBM Monochrome Display is attached to the
adapter, address 3B4 is used. If a color display is attached to the
adapter, address 3D4 is used. This register is loaded with a binary
value that points to the CRT Controller data register where data
is to be written. This value is referred to as "Index" in the table
above.
24 IBM Enhanced Graphics Adapter
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