这是我的第一个问题。该程序的本质是逐字符读取行，并禁止无关字符，如F1，F2，插入键等。或与CTRL组合（Ctrl+C =〉心形符号）
下面是我的部分代码：

main:
    mov si, 0
    mov ax,@data
    mov ds, ax
    lea dx,message 
    mov ah, 09h     ;print message
    int 21h
    mov ax, 40h                     ; load segment into AX
    mov es, ax
read_loop:        
    mov ah, 00h
    test byte ptr es:[17h], 04h     ; is CTRL pressed?
    jnz read_loop
    int 16h
    cmp al, 0       ;check ASCII
    jne ASCII
    mov ah, 00h
    int 16h
    jmp read_loop
ASCII:
    cmp ah, 14
    je read_loop
    cmp al, 13      ; ENTER?
    je next
    test byte ptr es:[17h], 04h     ; is CTRL pressed?
    jnz read_loop
    mov str_record[si], al
    mov ah, 02h     ; display
    mov dl, al
    int 21h
    inc si
    cmp si, 40  ;check max_len
    je next
    jmp read_loop
    
next:
    cmp str_record[0], '$'
    je quit
    mov al, 3
    int 10h
    mov di, 0
    mov ax, 3
    int 10h
    
    mov ah, 02h
    mov dh, 2
    mov dl, 15
    int 10h

我尝试使用Keyboard Shift Status Flags检查是否按下了ctrl，但当我释放该键时，将打印与CTRL沿着按下的所有按钮