boot.s

   1         bits 16 ; boot sectors run in real mode
   2         org 7c00h ; boot sector is loaded at 0x7c00
   3
   4 _start
   5         mov di, printing_numbers
   6         call print
   7
   8         or bl, 1
   9         mov dx, 0DEADh ; number to print
  10         call print_word
  11
  12         mov di, space
  13         call print
  14
  15         xor bl, bl
  16         mov dx, 0BEEFh
  17         call print_word
  18
  19         mov di, waiting
  20         call print
  21
  22         mov di, keystroke
  23         mov bl, 1
  24
  25 .loop
  26         mov ah, 0
  27         int 16h
  28         cmp ah, 1Ch
  29         je .enterpressed
  30         jmp .continue
  31         cmp ah, 0Eh
  32         je .backspace
  33         jmp .continue
  34 .enterpressed
  35         pusha
  36         mov ah, 0Eh
  37         mov al, 0Dh
  38         int 10h
  39         mov al, 0Ah
  40         int 10h
  41         popa
  42         jmp .loop
  43 .backspace
  44         pusha
  45         mov ah, 03h
  46         mov bh, 0
  47         int 10h
  48         dec dl
  49         mov ah, 02h
  50         int 10h
  51         mov ah, 0Eh
  52         mov al, ' '
  53         int 10h
  54         mov ah, 02h
  55         int 10h
  56         popa
  57         jmp .loop
  58 .continue
  59         mov [keystroke], al
  60         call print
  61         jmp .loop
  62
  63 printing_numbers db "Printing some random hex numbers", 0
  64 waiting db "I await keystrokes", 0
  65 keystroke db "$", 0
  66 space db " ", 0
  67
  68 %include "print.s"
  69
  70         times 510-($-$$) db 0 ; fill with 0 until 0x1fc is reached
  71         dw 0AA55h ; BIOS MBR signature