分析下列程序: DATA SEGMENT NUM DB 06H SUM DB? DATA ENDS STACK SEGMENT PARA STACK'STACK' STAPN DW 100 DUP(?) STACK ENDS CODE SEGMENT ASSUME CS:CODE,DS:DATA,SS:STACK START:MOV AX,DATA MOV DS,AX PUSH AX PUSH DX CALL AAA MOV AH,4CH INT 21H AAA PROC XOR AX,AX MOV DX,AX INC DL MOV CL,NUM MOV CH,00H BBB: ADD AL,DL DAA INC DL LOOP BBB MOV SUM,AL RET AAA ENDP CODE ENDS END START (1) 程序执行到MOVAH,4CH语句时,AX=?DX=?SP=? (2) BBB:ADD AL,DL语句的功能是什么? (3) 整个程序的功能是什么?