高手帮忙看看这个程序

DATA SEGMENT
     BUF1 DW 8234H,8234H,45H,23H,16H
     BUF2 DD   5 DUP(0)
DATA ENDS
CODE SEGMENT
    ASSUME CS:CODE,DS:DATA
START: MOV AX,DATA
       MOV DS,AX
       MOV ES,AX
       MOV CX,5
       MOV DI,0
    AA:MOV SI,OFFSET [BUF1+DI]
       MOV AX,[BUF1+DI]
       TEST AX,AX
       JS BB
       MOV AL,1
       MOV BYTE PTR [SI+2],AL
    BB:SHL AX,1
       MOV WORD PTR [BUF2+DI],AX
       LOOP AA
       MOV SI,OFFSET BUF2
       MOV BX,WORD PTR [BUF2]
       MOV DL,[SI+2]
       MOV AH,4CH
       INT 21H
CODE ENDS
END START

为什么执行完之后 DX中不是0001，而是0000？？？为什么 MOV AL,1
                                                     MOV BYTE PTR [SI+2],AL 就好像没执行一样？？？求教