Colored Hello World in TASM

Question

Good day. I'm new in assembly language and I'm trying to print a colored "Hello World" in TASM. Here is my code so far. It just prints "hello world" without a color.

.model small
.stack 100h

.data
message db 13,10,"Hello World!$"

.code
main proc near
   lea dx, message
   mov ah, 09h
   int 21h

   mov ah,4ch
   int 21h
main endp

I've read something like this

mov ah,9    ;Function 9: Write character and attribute at cursor position
mov al,'H'  ;AL = character to display
mov bh,0    ;BH = page number
mov bl,02EH ;BL = attribute (yellow on green)
mov cx,1    ;CX = number of times to write character
int 10H  ;Int 10H: Video (show the character)

in a forum but I can't incorporate it with my hello world. I'm confused why use that particular register and the like. Please help me. Thank you very much!

EDIT

.model small
.stack 100h

.data
hello db 'Hello World!',0

.code
main proc near
    mov ax, @data
    mov ds, ax

    mov ax, 3
    int 10h

    mov si, 0             ; cl is the counter register, set it to
                      ; zero (the first character in the string)

start:                ; Beginning of loop
    mov al, hello[si]   ; Read the next byte from memory
    cmp al, 0           ; Compare the byte to null (the terminator)
    je endthis              ; If the byte is null, jump out of the loop

    mov ah, 09h
    mov al, hello[si]
    mov bh, 0
    mov bl,02EH
    mov cx,11
    int 10H  

    add si, 1           ; Move to the next byte in the string
    jmp start           ; Loop

endthis:    
    mov ah, 4ch
    int 21h

main endp
end main

Answer 1

Assembly language, as any programming language, is a result of arbitrary design decisions. Sometimes there can be a reason why a specific register is used as a interrupt call input register (optimization), but many times not, and you just have to take the interface (here int 10h or int 21h) as granted.

Related to your problem with several exclamation marks !!!!!!!!!!! (I assume 11 exclamation marks), you have incorrect parameters in your int 10 interrupt call:

mov cx,11

According to Ralf Brown's Interrupt List, the parameters for mov ah,9, int 10h are the following:

INT 10 - VIDEO - WRITE CHARACTER AND ATTRIBUTE AT CURSOR POSITION
    AH = 09h
    AL = character to display
    BH = page number (00h to number of pages - 1) (see #00010)
        background color in 256-color graphics modes (ET4000)
    BL = attribute (text mode) or color (graphics mode)
        if bit 7 set in <256-color graphics mode, character is XOR'ed
          onto screen
    CX = number of times to write character
Return: nothing
Notes:  all characters are displayed, including CR, LF, and BS
    replication count in CX may produce an unpredictable result in graphics
      modes if it is greater than the number of positions remaining in the
      current row
    With PhysTechSoft's PTS ROM-DOS the BH, BL, and CX values are ignored
      on entry.

So, instead of mov cx,11, it should be mov cx,1.

And the second mov al, hello[si] is redundant, because hello[si] has already been loaded into al at that time with the previous identical instruction. This doesn't affect the functioning of the code, however.

Edit: Added info on how to set and read the cursor location using int 10h.

It seems that you also need to update the cursor location with mov ah,2, int 10h, using the following parameters:

INT 10 - VIDEO - SET CURSOR POSITION
    AH = 02h
    BH = page number
        0-3 in modes 2&3
        0-7 in modes 0&1
        0 in graphics modes
    DH = row (00h is top)
    DL = column (00h is left)
Return: nothing

Possibly you may need need to read the current cursor position with mov ah,3, int 10h, using the following parameters:

INT 10 - VIDEO - GET CURSOR POSITION AND SIZE
    AH = 03h
    BH = page number
        0-3 in modes 2&3
        0-7 in modes 0&1
        0 in graphics modes
Return: AX = 0000h (Phoenix BIOS)
    CH = start scan line
    CL = end scan line
    DH = row (00h is top)
    DL = column (00h is left)
Notes:  a separate cursor is maintained for each of up to 8 display pages
    many ROM BIOSes incorrectly return the default size for a color display
      (start 06h, end 07h) when a monochrome display is attached
    With PhysTechSoft's PTS ROM-DOS the BH value is ignored on entry.

Answer 2

If you're programming in assembly for DOS you should familiarize yourself with some of the commonly used interrupts, like int 10h and int 21h. For each interrupt subfunction there's a corresponding set of parameters that you need to pass to it through one or more registers.

The interrupt used in the example code you pasted is "WRITE CHARACTER AND ATTRIBUTE AT CURSOR POSITION", and you can find its description here.

In order to display a string with color attributes you'll have to iterate over the string in a loop and invoke the interrupt for each character with the appropriate parameters.

Answer 3

.model small
.data
msg1 10,13,"hellow $"
.code
.startup
mov ah,09h
int 21h
.exit
end