User:Johnburger/Demo/Dev/VGA

The memory arrangement of the Text mode of the IBM PC is a linear array of two-byte locations. The first memory location is the top left of the screen, followed by 79 (typically) more locations for the first row, immediately followed by the memory for the second row, until all the rows are displayed. Each screen location is two bytes:

• The first byte is the character code, which (luckily) is ASCII for the characters #32-#126 - most text is easy to display. The other codes in the #0-#255 range are often called "OEM" codes - different countries use different codes. The default mapping is used in this system.
• The second byte is that character's attribute - typically its colour. The low nybble is the foreground colour, while the high nybble is the background colour - except for the highest bit, which is often set to flash the character. Many systems though don't do this, instead substituting a wider range of shades of colours.

The colours available to display are essentially the primary RGB and the secondary CMY, with the necessary White and Black added in.

Demo/Dev/VGA.inc

;
; Dev/VGA.inc
;

; These are the definitions for the Video Graphics Array (VGA) Controller.
;
; The memory arrangement of the Text mode of the IBM PC is a linear array of
; two-byte locations. The first memory location is the top left of the screen,
; followed by 79 (typically) more locations for the first row, immediately
; followed by the memory for the second row, until all the rows are displayed.
; Each screen location is two bytes:
;
; The first byte is the character code, which (luckily) is ASCII for the
; characters #32-#126 - most text is easy to display. The other codes in the
; #0-#255 range are often called "OEM" codes - different countries use different
; codes. The default mapping is used in this system.
;
; The second byte is that character's attribute - typically its colour. The low
; nybble is the foreground colour, while the high nybble is the background
; colour - except for the highest bit, which is often set to flash the
; character. Many systems though don't do this, instead substituting a wider
; range of shades of colours.
;
; The colours available to display are essentially the primary RGB and the
; secondary CMY, with the necessary White and Black added in. The table for the
; default colour mappings is provided below.

Dev.VGA.Base      EQU           000B_8000h      ; Base memory address

Dev.VGA.Foregruond EQU          0000_1111b
Dev.VGA.Bright     EQU          0000_1000b
Dev.VGA.Background EQU          0111_0000b
Dev.VGA.Blink      EQU          1000_0000b

Dev.VGA.Black     EQU           0_0h
Dev.VGA.Blue      EQU           0_1h
Dev.VGA.Green     EQU           0_2h
Dev.VGA.Cyan      EQU           0_3h
Dev.VGA.Red       EQU           0_4h
Dev.VGA.Magenta   EQU           0_5h
Dev.VGA.Brown     EQU           0_6h
Dev.VGA.Grey      EQU           0_7h

Dev.VGA.Dark          EQU       Dev.VGA.Bright | Dev.VGA.Black
Dev.VGA.BrightBlue    EQU       Dev.VGA.Bright | Dev.VGA.Blue
Dev.VGA.BrightGreen   EQU       Dev.VGA.Bright | Dev.VGA.Green
Dev.VGA.BrightCyan    EQU       Dev.VGA.Bright | Dev.VGA.Cyan
Dev.VGA.BrightRed     EQU       Dev.VGA.Bright | Dev.VGA.Red
Dev.VGA.BrightMagenta EQU       Dev.VGA.Bright | Dev.VGA.Magenta
Dev.VGA.Yellow        EQU       Dev.VGA.Bright | Dev.VGA.Brown
Dev.VGA.White         EQU       Dev.VGA.Bright | Dev.VGA.Grey

Dev.VGA.BlackBack     EQU       Dev.VGA.Black   << 4
Dev.VGA.BlueBack      EQU       Dev.VGA.Blue    << 4
Dev.VGA.GreenBack     EQU       Dev.VGA.Green   << 4
Dev.VGA.CyanBack      EQU       Dev.VGA.Cyan    << 4
Dev.VGA.RedBack       EQU       Dev.VGA.Red     << 4
Dev.VGA.MagentaBack   EQU       Dev.VGA.Magenta << 4
Dev.VGA.YellowBack    EQU       Dev.VGA.Brown   << 4
Dev.VGA.WhiteBack     EQU       Dev.VGA.Grey    << 4

Dev.VGA.Misc.Port EQU           3C2h            ; VGA miscellaneous port

Dev.VGA.Seq.Base  EQU           3C4h            ; VGA Sequencer base port

Dev.VGA.CRTC.Base EQU           3D4h            ; VGA CRTC base port