DATA1 DB 'ABCDEFGHIJKLMNOPQRST'
  ORG 30H
  DATA2 DB 20 DUP (?)
  MOV AX,@DATA
  MOV DS,AX 
  MOV ES,AX 
  CLD 
  MOV SI,OFFSET DATA1 
  MOV DI,OFFSET DATA2 
  MOV CX,20 
  REP MOVSB