fasm_4_3

org 100h

   ESC_ equ 01bh ;ascii code of escape
   BELL_ equ 7 ;ascii code of ring

   W_SS_ equ 11h
   A_SS_ equ 1Eh
   S_SS_ equ 1Fh
   D_SS_ equ 20h

start_:
    mov ah, 09h ;output - helloStr
    mov dx, helloStr_
    int 21h
main_:
    mov ah, 00h ;no echo input with waiting - output ah-scancode, al-ascii code
    int 16h
    cmp al, ESC_ ; escape ?
    je exit_ ;if yes exit
    jmp other_ ;if no go to other_
other_:
    cmp ah, W_SS_ ;if scancode is less than W it's incorrect, jump to not_allowed_key
    jb not_allowed_key ;jump if below W
    cmp ah, D_SS_ ;if scancode is greater than D it's incorrect, jump to not_allowed_key
    ja not_allowed_key ;jump if above D
    cmp ah, A_SS_
    jb check_if_W_ ;jump if below A
is_WASD:
    push ds ;save data segment
    mov bx, 40h ;mov 40h to bx
    mov ds, bx ;mov 40h to ds
    mov bx, 17h ;mov 17h to bx
    mov al, byte [bx] ;keyboard flags are at the address 40h:17h
    and al, 04h ;3rd bit is ctrl flag
    pop ds ;retrieve data segment
    cmp al, 04h ;is ctrl pressed?
    jne not_allowed_key ;if no jump to not_allowed_key
    mov bx, ctrlStr_ ;if yes mov address of first symbol of "ctrl+0" to bx
    add bx, 5 ;offset to "0" in "SHIFT+0"
    cmp ah, A_SS_ ;was the letter A?
    je ctrl_a_ ;if yes jump to ctrl_a_
    cmp ah, W_SS_ ;etc.....
    je ctrl_w_
    cmp ah, S_SS_
    je ctrl_s_
    jmp ctrl_d_
check_if_W_:
    cmp ah, W_SS_
    je is_WASD
    jmp not_allowed_key
not_allowed_key:
    mov ah, 02h
    mov dl, 07h ; sound
    int 21h
    jmp main_ ;go back to start
displ_comb_:
    mov ah, 09h ;set text property of next...
    mov cx, 6 ;...6 characters (next 6 characters will have color set in bl)
    int 10h
    mov dx, ctrlStr_ ;output that string
    int 21h
    jmp main_
ctrl_a_:
    mov byte [bx], 'A' ;in bx address of "0", change it to correct letter
    xor bh, bh ;clear bh
    mov bl, $4F ;set color
    jmp displ_comb_ ;jump to displ_comb_
ctrl_w_:
    mov byte [bx], 'W'
    xor bh, bh
    mov bl, $0F
    jmp displ_comb_
ctrl_s_:
    mov byte [bx], 'S'
    xor bh, bh
    mov bl, $20
    jmp displ_comb_
ctrl_d_:
    mov byte [bx], 'D'
    xor bh, bh
    mov bl, $10
    jmp displ_comb_
exit_:
    mov ah, 09h ;output - byeStr
    mov dx, byeStr
    int 21h
    mov ah, 07h ;wait for input
    int 21h
    ret

helloStr_ db "This program changes text properties", $0d, $0a, "You can exit on ESC", $0d, $0a, "Try to input CTRL + W, A, S, D:", $0d, $0a, "$"
byeStr db 0dh, 0ah, "Press anything to terminate the program...$"
ctrlStr_ db "ctrl+0 $"