The VGA is upwardly-compatible with the CGA, MDA, and EGA in that all

commonly-used I/O activities are emulated at the expected port addresses.

Video programming at the hardware port level has become increasingly

difficult and risky while the BIOS programming interface has become

flexible and comprehensive.  It is recommended that you use the BIOS

functions when possible.  See INT 10H (video services).

The following table lists ports and indexes for the VGA without providing

full details.  Since the VGA uses the same port range as the EGA, you may

refer to EGA I/O Ports and CGA I/O Ports for related information.

Port  Description

3c0H  Attribute Address Register (read/write)

3c0H  Palette Registers / Other Attribute Registers (write)

Index: 00H   0fH  Palette registers

10H  mode control

11H  overscan (border) color

12H  enable color planes

13H  horizontal pixel panning

14H  color select register

3c1H  Palette Registers (read)

3c2H  Miscellaneous Output Register (write)

3c2H  Input Status Register 0 (read)

3c3H  VGA Enable Register (read/write)

3c4H  Sequencer Address Register (read/write)

3c5H  Other Sequencer Registers (read/write)

Index: 00H  reset

01H  Clocking Mode

02H  Map Mask

03H  Character Map Select

04H  Memory Mode

3c6H  PEL Mask Register

3c7H  PEL Address Register for Read Mode (write)

3c7H  DAC State Register (read)

3c8H  PEL Address Register for Write Mode (read)

3c9H  PEL Data Register

3caH  Feature Control Register (read)

3ccH  Miscellaneous Output Register (read)

3ceH  Graphics Address Register

3cfH  Other Graphics Registers

Index: 00H  set/reset

01H  enable set/reset

02H  color compare

03H  data rotate

04H  read map select

05H  graphics mode register

06H  miscellaneous graphics control

07H  color don't care

08H  plane bit mask

3?4H  CRT controller address (3b4H=MDA emulation, 3d4H=CGA emulation)

3?5H  CRT controller internal registers

Index: 00H  horizontal total

02H  start horizontal blanking (character count)

03H  end horizontal blanking

04H  start horizontal retrace (character position)

05H  end horizontal retrace

06H  vertical total (scan lines)

07H  overflow (bit 8 for certain CRTC registers)

08H  preset row scan; first scan line after vertical retrace

09H  maximum scan line

0aH  cursor start

0bH  cursor end

0cH  regen start address (high)

0dH  regen start address (low)

0eH  Cursor location (high)

0fH  Cursor location (low)

10H  vertical retrace start

11H  vertical retrace end

12H  vertical displayed end (scan line)

13H  vertical displayed adjustment

14H  underline location.  Bits 0-5 are scan line number.

15H  start vertical blanking (scan line)

16H  end vertical blanking

17H  mode control

18H  line compare (scan line)  Used for split screen

3?aH  Feature Control Register (write) (3baH=mono emulation, 3daH=CGA emul.)

3?aH  Input Status Register 1 (read)

See Also: EGA I/O Ports

CGA I/O Ports

EGA/VGA Data Areas

INT 10H (BIOS video services)

I/O Port Map

Cables and Pin Outs

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