4. 阅读下面的程序段，写出主要指令的注释并分析程序实现的功能。DATA SEGMENTDATA1 DB ‘ABCDEFG’DATA ENDSCODE SEGMENT ASSUME CS:CODE,DS:DATAAAA
A:MOV AX,DATAMOV DS,AXMOV BX,OFFSET DATA1MOV CX,7NEXT:MOV AH,2MOV AL,[BX]XCHG AL,DLINC BXINT 21HLOOP NEXTMOV AH,4CHINT 21HCODE ENDS END AAAA