
CRT Controller Registers
9-1
`efmp69030 Databook
Revision 1.3 11/24/99
Chapter 9
CRT Controller Registers
Introduction
The CRT controller registers are accessed by writing the index of the desired register into the CRT
Controller Index Register at I/O address 3B4h or 3D4h (depending upon whether the graphics system is
configured for MDA or CGA emulation), and then accessing the desired register through the data port for
the CRT controller registers located at I/O address 3B5h or 3D5h (again depending upon the choice of MDA
or CGA emulation)
Name
Register Function
Access
3B5/3D5
Index Value
3B4/3D4 (CRX)
CR00
Horizontal Total Register
read/write
00h
CR01
Horizontal Display Enable End Register
read/write
01h
CR02
Horizontal Blanking Start Register
read/write
02h
CR03
Horizontal Blanking End Register
read/write
03h
CR04
Horizontal Sync Start Register
read/write
04h
CR05
Horizontal Sync End Register
read/write
05h
CR06
Vertical Total Register
read/write
06h
CR07
Overflow Register
read/write
07h
CR08
Preset Row Scan Register
read/write
08h
CR09
Maximum Scanline Register
read/write
09h
CR0A
Text Cursor Start Scanline Register
read/write
0Ah
CR0B
Text Cursor End Scanline Register
read/write
0Bh
CR0C
Start Address High Register
read/write
0Ch
CR0D
Start Address Low Register
read/write
0Dh
CR0E
Text Cursor Location High Register
read/write
0Eh
CR0F
Text Cursor Location Low Register
read/write
0Fh
CR10
Vertical Sync Start Register
read/write
10h
CR11
Vertical Sync End Register
read/write
11h
CR12
Vertical Display Enable End Register
read/write
12h
CR13
Offset Register
read/write
13h
CR14
Underline Row Register
read/write
14h
CR15
Vertical Blanking Start Register
read/write
15h
CR16
Vertical Blanking End Register
read/write
16h
CR17
CRT Mode Control Register
read/write
17h
CR18
Line Compare Register
read/write
18h
CR22
Memory Read Latch Data Register
read-only
22h
CR30
Extended Vertical Total Register
read/write
30h
CR31
Extended Vertical Display End Register
read/write
31h
CR32
Extended Vertical Sync Start Register
read/write
32h
CR33
Extended Vertical Blanking Start Register
read/write
33h
CR38
Extended Horizontal Total Register
read/write
38h
CR3C
Extended Horizontal Blanking End Register
read/write
3Ch
CR40
Extended Start Address Register
read/write
40h
CR41
Extended Span Register (shadowed)
read/write
41h
CR70
Interlace Control Register
read/write
70h
CR71
NTSC/PAL Video Output Control Register
read/write
71h
CR72
NTSC/PAL Horizontal Serration 1 Start Register
read/write
72h
CR73
NTSC/PAL Horizontal Serration 2 Start Register
read/write
73h
CR74
NTSC/PAL Horizontal Pulse Width Register
read/write
74h
CR75
NTSC/PAL Filtering Burst Read Length Register
read/write
75h
CR76
NTSC/PAL Filtering Burst Read Quantity Register
read/write
76h
CR77
NTSC/PAL Filtering Control Register
read/write
77h
CR78
NTSC/PAL Vertical Reduction Register
read/write
78h
CR79
NTSC/PAL Pixel Resolution Fine Adjust Register
read/write
79h