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Changing Text Colour with NASM Assembly

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MichaelSammels MichaelSammels is offline

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Changing Text Colour with NASM Assembly

Oct 12th, 2009

Does anyone know how to change the colour of strings using x86 NASM Assembler? I've found tutorials like this:

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 Assembly Syntax (Toggle Plain Text) 
mov  ah,  09h 
mov  al,  97 
mov  bx,  100b
mov  cx,  01h 
int  10h
mov  ah,  09h 
mov  al,  97 
mov  bx,  100b
mov  cx,  01h 
int  10h

Which prints the letter "A" once in the colour you choose. This is a handy tutorial, but I would like to be able to print the entire screen text (i.e more than one string) in the same colour. Anyone have any ideas?

Last edited by MichaelSammels; Oct 12th, 2009 at 8:01 am.

Thanks,

Michael

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NotNull

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Junior Poster

Oct 13th, 2009

Color text-mode memory lies at segment 0xb800 and is 4000 bytes
in length 80*25*2 cuz each visible character on the screen
is accompanied by a text attribute byte.
00000000 Text Attribute Byte
XXBGxxFG
The low-nibble defines the foreground and the high-nibble
the background, and there is a way to disable the blink
bit.

Function 9 - Output Char And Attribute At Hardware Cursor
CX-Repeat
BH-Display Page
BL-Attribute
AL-Character
AH-9
INT 0x10

To clear the screen to one f/b color try this code:

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 Assembly Syntax (Toggle Plain Text) 
clrscr:
mov dx, 0 ; Set cursor to top left-most corner of screen
mov bh, 0
mov ah, 0x2
int 0x10
mov cx, 2000 ; print 2000 chars
mov bh, 0
mov bl, 0x21 ; green bg/blue fg
mov al, 0x20 ; blank char
mov ah, 0x9
int 0x10
ret
clrscr:
mov dx, 0 ; Set cursor to top left-most corner of screen
mov bh, 0
mov ah, 0x2
int 0x10
mov cx, 2000 ; print 2000 chars
mov bh, 0
mov bl, 0x21 ; green bg/blue fg
mov al, 0x20 ; blank char
mov ah, 0x9
int 0x10
ret

This code writes a blue 'A' char to 0,0:

 Help with Code Tags 
 Assembly Syntax (Toggle Plain Text) 
mov cx, 0xb800
mov es, cx
mov ax, 0x141
mov [es:0], ax
waitkey:
mov ah, 0x6
mov dl, 0xff
int 0x21
jz waitkey
ret
mov cx, 0xb800
mov es, cx
mov ax, 0x141
mov [es:0], ax
waitkey:
mov ah, 0x6
mov dl, 0xff
int 0x21
jz waitkey
ret

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