jump.asm

.model small
.stack 100h
.data

  a db ?
.code  

main proc 
     
     mov ax, @data
     mov ds, ax 
     
  input:
     mov ah, 1
     int 21h  
     ;caution without al register variable cannot hold value
     mov a, al     
     
     cmp a, 'X'
     je exit
     
  output:
     mov ah, 2
     mov dl, 0ah
     int 21h
     mov dl, 0dh
     int 21h
     mov dl,a
     int 21h
      mov dl, 0ah
     int 21h
     mov dl, 0dh
     int 21h  
    ;nonconditional jump 
     jmp input                        
     
  exit:    
     ; successful termination
     mov dl, 4ch
     int 21h
    
    
    main endp
end main