mov eax,3
mov ebx,0
mov ecx,X
mov edx,2
int 80h

mov cx,[X]
xor cx,1
mov [X],cx

mov eax,4
mov ebx,1
mov ecx,X
mov edx,2
int 80h

mov eax,1
mov ebx,0
int 80h

section .data
X dw 0