program segment                             ;define code segment
main proc far
           assume cs:program
   start:
    ;set up stack for return
           push ds                          ;save old data segment
           sub ax,ax                        ;put zero in AX
           push ax                          ;save zero on stack
    ;main part of program
           mov ch,4                         ;number of digits
   rotate: mov cl,4                         ;set count to 4 bits
           rol bx,cl                        ;left digit to right
           mov al,bl                        ;move to AL
     and   al,ofh                           ;mask off left dight
     and   al,30h                           ;convert hex to ASCII
     cmp   al,3ah                           ;is it>9?
     jl    printit                          ;jump if digit=0 to 9
     add   al,7h                            ;digit si A to F
   printit
           mov dl,al                        ;put ASCII char in DL
           mov ah,2                         ;display output funct
           int 21h                          ;call DOS
           dec ch                           ;done 4 digits?
           jnz rotate                       ;not yet
           ret                              ;return to DOS
    main   endp

   program ends                             ;end of segment
           end                              ;end of assembly