Color Graphics Adapter
3D4h 6845 Index Register (Output)
3D5h 6845 Data Registers
Reg# Meaning Text Graphics Unit
R0 Horizontal Total 97 53 Char
R1 Horizontal Displayed 80 45 Char
R2 H.Sync position 82 46 Char
R3 H.Sync width 15 8 Char
R4 Vertical Total 25 91 Rows
R5 Vertical Adjust 6 2 Lines
R6 Vertical Displayed 25 87 Char
R7 V.Sync Position 25 87 Rows
R8 Interlace Mode 2 2
R9 Max.ScanLine Address 13 3
R10 Horizontal Display 12 0 Lines
R11 Horizontal Display 0 0 Lines
R12 Screen Start Address (H) 0 0
R13 Screen Start Address (L) 0 0
R14 Cursor Address (H) 0 0
R15 Cursor Address (L) 0 0
3D8h Mode Register (Output)
Bit
7 6 5 4 3 2 1 0
x x . . . . . . not used
. . x . . . . . Blinking
. . . x . . . . 640x200 B&W
. . . . x . . . Enable Video
. . . . . x . . B&W Mode
. . . . . . x . 320x200 Graphics
. . . . . . . x 80x25 Mode
3D9h Color Register (Output)
Bit
7 6 5 4 3 2 1 0
x x . . . . . . not used
. . x . . . . . 320x200 Color set
. . . x . . . . Alt. Back Colors
. . . . x . . . Intensify RGB
. . . . . x . . Blue
. . . . . . x . Green
. . . . . . . x Red
3DAh Status Register (Input)
Bit
7 6 5 4 3 2 1 0
x x x x . . . . not used
. . . . x . . . Alpha Data
. . . . . x . . Pen Switch off
. . . . . . x . Light Pen Triggered
. . . . . . . x Video Sync
3DBh Clear Light pen Latch (Output)
3DCh Set Light pen Latch (Output)