DSEG   SEGMENT
  DATA   DB 12H
  SUM    DB 0
  DSEG   ENDS
  SSEG   SEGMENT STACK
         DB 512 DUP(0)
  SSEG   ENDS
  CSEG   SEGMENT
         ASSUME DS:DSEG,SS:SSEG,CS:CSEG
  START: MOV AX,DSEG
         MOV DS,AX
         MOV AL,DATA
         ADD AL,16H
         MOV SUM,AL
         MOV AH,4CH
         INT 21H
  CSEG   ENDS
         END START