Subtraction of two numbers

Write an assembly Language Programming for subtraction of two numbers.

data segment
ends
stack segment
    dw   128  dup(0)
ends
code segment
start:
mov ax,1001h
mov bx,2001h
sub bx,ax
mov dx,bx   
mov ax, 4c00h
int 21h 
ends
end start

Some Tips are written in the Addition of two numbers program.