assume cs:code

 code segment
 start:
     mov ax, cs
     mov ds, ax
     mov si, offset sqr

     mov es, ax
     mov di, 200h
     mov cx, offset sqrend - offset sqr
     cld
     rep movsb

     mov es, ax
     +], 200h
      + ], 

     mov ax, 4c00h
     int 21h

 sqr:
     mul ax
     iret
 sqrend:
     nop

 code ends

 end start

 assume cs:code

 code segment
 start:

     int 7ch
     add ax, ax
     adc dx, dx

     mov ax, 4c00h
     int 21h
 code ends

 end start