简答题 阅读下面的程序段,试说明它实现的功能是什么? DATA SEGMENT DATA1 DB 'ABCDEFG' DATA ENDS CODE SEGMENT ASSUME CS:CODE,DS:DATA AAAA:MOV AX,DATA MOV DS,AX MOV BX,OFFSET DATA1 MOV CX,7 NEXT:MOV AH,2 MOV AL,[BX] XCHG AL,DL INC BX INT 21H LOOP NEXT MOV AH,4CH INT 21H CODE ENDS END AAAA