4_3

    org 100h

    ESC_ equ 01bh ;ascii code of escape
    BELL_ equ 7 ;ascii code of ring
    Q_SS_ equ 10h ;scancode of q
    W_SS_ equ 11h ;scancode of w
    E_SS_ equ 12h ;scancode of e
    R_SS_ equ 13h ;scancode of r

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_ ;was it escape?
    jne other_ ;if no go to other_
    jmp exit_ ;if yes exit
other_:
    cmp ah, Q_SS_ ;if scancode is less than Q it's incorrect, jump to err_
    jb err_ ;jump if below
    cmp ah, R_SS_ ;if scancode is greater than R it's incorrect, jump to err_
    ja err_ ;jump if above
    push ds ;save data segment
    mov bx, 40h ;mov 40h to bx
    mov ds, bx ;mov 40h to ds (you cannot use immediate value here)
    mov bx, 17h ;mov 17h to bx
    mov al, byte [bx] ;keyboard flags are at the address 40h:17h
    and al, 02h ;second bit is shift flag
    pop ds ;retrieve data segment
    cmp al, 02h ;is shift pressed?
    jne err_ ;if no jump to err_
    mov bx, shiftStr_ ;if yes mov address of first symbol of "SHIFT+0" to bx
    add bx, 6 ;offset to "0" in "SHIFT+0"
    cmp ah, Q_SS_ ;was the letter Q?
    je shift_q_ ;if yes jump to shift_q_
    cmp ah, W_SS_ ;etc.....
    je shift_w_
    cmp ah, E_SS_
    je shift_e_
    cmp ah, R_SS_
    je shift_r_
err_:
    mov ah, 02h ;play ring
    mov dl, BELL_
    int 21h
    jmp main_ ;go back to start
displ_comb_:
    mov ah, 09h ;set text property of next...
    mov cx, 7 ;...7 characters (next 7 characters will have color set in bl)
    int 10h
    mov dx, shiftStr_ ;output that string
    int 21h
    jmp main_
shift_q_:
    mov byte [bx], 'Q' ;in bx address of "0", change it to correct letter
    xor bh, bh ;clear bh
    mov bl, 1fh ;set color
    jmp displ_comb_ ;jump to displ_comb_
shift_w_:
    mov byte [bx], 'W'
    xor bh, bh
    mov bl, 20h
    jmp displ_comb_
shift_e_:
    mov byte [bx], 'E'
    xor bh, bh
    mov bl, 0f4h
    jmp displ_comb_
shift_r_:
    mov byte [bx], 'R'
    xor bh, bh
    mov bl, 06h
    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 SHIFT + Q, W, E, R:", $0d, $0a, "$"
byeStr db 0dh, 0ah, "The program has now terminated. Press anything to continue...$"
shiftStr_ db "SHIFT+0 $"