More VGA tests
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Jeff Parsons
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9b4761e35c
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141b7db85d
5 changed files with 534 additions and 2 deletions
230
tests/pc/vga/L25-1.ASM
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230
tests/pc/vga/L25-1.ASM
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; Program to illustrate operation of data rotate and bit mask
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; features of Graphics Controller. Draws 8x8 character at
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; specified location, using VGA's 8x8 ROM font. Designed
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; for use with modes 0Dh, 0Eh, 0Fh, 10h, and 12h.
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; By Michael Abrash.
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;
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stack segment para stack ‘STACK'
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db 512 dup(?)
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stack ends
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;
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VGA_VIDEO_SEGMENT equ 0a000h ;VGA display memory segment
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SCREEN_WIDTH_IN_BYTES equ 044ah ;offset of BIOS variable
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FONT_CHARACTER_SIZE equ 8 ;# bytes in each font char
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;
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; VGA register equates.
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;
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GC_INDEX equ 3ceh ;GC index register
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GC_ROTATE equ 3 ;GC data rotate/logical function
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; register index
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GC_BIT_MASK equ 8 ;GC bit mask register index
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;
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dseg segment para common ‘DATA'
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TEST_TEXT_ROW equ 69 ;row to display test text at
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TEST_TEXT_COL equ 17 ;column to display test text at
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TEST_TEXT_WIDTH equ 8 ;width of a character in pixels
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TestString label byte
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db ‘Hello, world!',0 ;test string to print.
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FontPointer dd ? ;font offset
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dseg ends
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;
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; Macro to set indexed register INDEX of GC chip to SETTING.
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;
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SETGC macro INDEX, SETTING
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mov dx,GC_INDEX
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mov ax,(SETTING SHL 8) OR INDEX
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out dx,ax
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endm
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;
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cseg segment para public ‘CODE'
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assume cs:cseg, ds:dseg
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start proc near
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mov ax,dseg
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mov ds,ax
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;
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; Select 640x480 graphics mode.
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;
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mov ax,012h
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int 10h
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;
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; Set driver to use the 8x8 font.
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;
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mov ah,11h ;VGA BIOS character generator function,
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mov al,30h ; return info subfunction
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mov bh,3;get 8x8 font pointer
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int 10h
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call SelectFont
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;
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; Print the test string.
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;
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mov si,offset TestString
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mov bx,TEST_TEXT_ROW
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mov cx,TEST_TEXT_COL
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StringOutLoop:
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lodsb
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and al,al
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jz StringOutDone
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call DrawChar
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add cx,TEST_TEXT_WIDTH
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jmp StringOutLoop
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StringOutDone:
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;
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; Reset the data rotate and bit mask registers.
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;
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SETGC GC_ROTATE, 0
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SETGC GC_BIT_MASK, 0ffh
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;
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; Wait for a keystroke.
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;
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mov ah,1
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int 21h
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;
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; Return to text mode.
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;
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mov ax,03h
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int 10h
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;
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; Exit to DOS.
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;
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mov ah,4ch
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int 21h
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Start endp
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;
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; Subroutine to draw a text character in a linear graphics mode
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; (0Dh, 0Eh, 0Fh, 010h, 012h).
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; Font used should be pointed to by FontPointer.
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;
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; Input:
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; AL = character to draw
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; BX = row to draw text character at
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; CX = column to draw text character at
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;
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; Forces ALU function to "move".
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;
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DrawChar proc near
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push ax
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push bx
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push cx
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push dx
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push si
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push di
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push bp
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push ds
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;
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; Set DS:SI to point to font and ES to point to display memory.
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;
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lds si,[FontPointer] ;point to font
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mov dx,VGA_VIDEO_SEGMENT
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mov es,dx ;point to display memory
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;
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; Calculate screen address of byte character starts in.
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;
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push ds ;point to BIOS data segment
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sub dx,dx
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mov ds,dx
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xchg ax,bx
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mov di,ds:[SCREEN_WIDTH_IN_BYTES] ;retrieve BIOS
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; screen width
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pop ds
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mul di ;calculate offset of start of row
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push di ;set aside screen width
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mov di,cx ;set aside the column
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and cl,0111b ;keep only the column in-byte address
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shr di,1
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shr di,1
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shr di,1 ;divide column by 8 to make a byte address
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add di,ax ;and point to byte
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;
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; Calculate font address of character.
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;
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sub bh,bh
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shl bx,1 ;assumes 8 bytes per character; use
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shl bx,1 ; a multiply otherwise
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shl bx,1 ;offset in font of character
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add si,bx ;offset in font segment of character
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;
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; Set up the GC rotation.
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;
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mov dx,GC_INDEX
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mov al,GC_ROTATE
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mov ah,cl
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out dx,ax
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;
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; Set up BH as bit mask for left half,
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; BL as rotation for right half.
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;
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mov bx,0ffffh
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shr bh,cl
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neg cl
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add cl,8
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shl bl,cl
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;
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; Draw the character, left half first, then right half in the
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; succeeding byte, using the data rotation to position the character
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; across the byte boundary and then using the bit mask to get the
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; proper portion of the character into each byte.
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; Does not check for case where character is byte-aligned and
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; no rotation and only one write is required.
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;
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mov bp,FONT_CHARACTER_SIZE
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mov dx,GC_INDEX
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pop cx ;get back screen width
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dec cx
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dec cx ; -2 because do two bytes for each char
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CharacterLoop:
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;
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; Set the bit mask for the left half of the character.
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;
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mov al,GC_BIT_MASK
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mov ah,bh
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out dx,ax
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;
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; Get the next character byte & write it to display memory.
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; (Left half of character.)
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;
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mov al,[si] ;get character byte
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mov ah,es:[di] ;load latches
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stosb ;write character byte
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;
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; Set the bit mask for the right half of the character.
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;
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mov al,GC_BIT_MASK
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mov ah,bl
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out dx,ax
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;
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; Get the character byte again & write it to display memory.
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; (Right half of character.)
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;
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lodsb ;get character byte
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mov ah,es:[di] ;load latches
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stosb ;write character byte
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;
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; Point to next line of character in display memory.
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;
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add di,cx
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;
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dec bp
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jnz CharacterLoop
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;
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pop ds
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pop bp
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pop di
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pop si
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pop dx
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pop cx
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pop bx
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pop ax
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ret
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DrawChar endp
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;
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; Set the pointer to the font to draw from to ES:BP.
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;
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SelectFont proc near
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mov word ptr [FontPointer],bp ;save pointer
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mov word ptr [FontPointer+2],es
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ret
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SelectFont endp
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;
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cseg ends
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end start
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