8086对字符串的处理和显示

DATAS SEGMENT
    DAT   DB 20 DUP($)
    INPUT DB "Please input :",0AH,0DH,'$'
DATAS ENDS

CODES SEGMENT
    ASSUME CS:CODES,DS:DATAS,SS:STACKS
START:
    MOV AX,DATAS
    MOV DS,AX
    MOV DX,OFFSET INPUT     ;显示输入指令
        MOV AH,9
        INT 21H
    MOV BP,0
    MOV CX,100     
LET2:
    MOV AH,1
    INT 21H
    CMP AL,13
    JE TT1
    CMP AL,97
    JNL TT3
    CMP AL,65
    JNL TT4         
    TT2:       
    LOOP LET2         ;此循环存入字母，排除数字与空格
    TT3:SUB AL,32
    MOV DAT[BP],AL
    INC BP
    JMP TT2