如圖1所示，將8255的C端口接8個發(fā)光二極管，用按位置位/復位控制字，使這8個發(fā)光二極管依次亮滅，其中74LS138譯碼器與地址總線已經(jīng)連接正確。

閱讀下面的程序，回答問題
DATA SEGMENT
BUF DB '1234'
N=$-BUF
BCD DB N DUP(?)
DATA ENDS
CODE SEGMENT
ASSUME CS:CODE,DS:DATA
START：MOV AX,DATA
MOV DS,AX
LEA SI,BUF
MOV CX,N
LEA DI,BCD+N-1
LOOP1：MOV AL,[SI]
SUB AL,30H
MOV [DI],AL
INC SI
DEC DI
DEC CX
JNE LOOP1
MOV AH,4CH
INT 21H
CODE ENDS
END START

閱讀下面的程序，回答問題
DATA SEGMENT
BUF DB '1234'
N=$-BUF
BCD DB N DUP(?)
DATA ENDS
CODE SEGMENT
ASSUME CS:CODE,DS:DATA
START：MOV AX,DATA
MOV DS,AX
LEA SI,BUF
MOV CX,N
LEA DI,BCD+N-1
LOOP1：MOV AL,[SI]
SUB AL,30H
MOV [DI],AL
INC SI
DEC DI
DEC CX
JNE LOOP1
MOV AH,4CH
INT 21H
CODE ENDS
END START

閱讀下面的程序，回答問題
DATA SEGMENT
BUF DB '1234'
N=$-BUF
BCD DB N DUP(?)
DATA ENDS
CODE SEGMENT
ASSUME CS:CODE,DS:DATA
START：MOV AX,DATA
MOV DS,AX
LEA SI,BUF
MOV CX,N
LEA DI,BCD+N-1
LOOP1：MOV AL,[SI]
SUB AL,30H
MOV [DI],AL
INC SI
DEC DI
DEC CX
JNE LOOP1
MOV AH,4CH
INT 21H
CODE ENDS
END START