CODEWITHSUNDEEP
assemblynasmx86-16bootloaderbios
Leonardo
Leonardo

Reputation: 83

Print a character from a variable using BIOS routine INT10h

Does somebody know what's wrong with the following code?

I cannot make it to work the way I want it. I just want to print a single character of a variable (the letter 'h').

To do that I just copy contents using indirect addressing via the square brackets

[]

; Set BIOS print screen settings
mov ah, 0x0e ; Teletype
mov bh, 0  ; Page number
mov bl, 4  ; Red on black (00000100 - High 0000 is black, low 0100 is red)
mov cx, 1  ; Writes one character

; Printing to screen
mov al, [msg] ; Copy the contents of 'H' into 'al'; IT SEEMS THIS IS NOT WORKING!!!
jmp print_char ; Jump to executable code and do not let CPU step on DATA SECTION

; [BEG DATA SECTION]
  msg: db 'HELLO', 0
; [END DATA SECTION]

print_char:
int 0x10 ; Call BIOS routine to print the char located at 'al'

infinite_loop:
jmp $
times 510 -($-$$) db 0 ; Pad with 0 until byte 510
dw 0xAA55 ; MBR Boot code signature

What I get is a screen that prints "nothing" (Probably an ASCII non-printable character: enter image description here

Upvotes: 2

Views: 1863

Answers (1)

Leonardo
Leonardo

Reputation: 83

The problem was that it was lacking the following instruction at the top:

org 0x7c00

More info regarding this in the answer of @Michael Petch.

Upvotes: 6

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