Go4Expert - help needed wid 8085 alp!

Hello,
Could you pls help me answer this question:
- Please take a look at my small Assembly program that reads a tring from keyboard, then displays all the characters that are not uper-case letters in reverse order:

Code:

.model small

.stack 100

.data

        tb1 db 'Pls enter a string, enter to finish $'

        tb2 db 10,13,'The characters that are not uper-case : $'

        xau db 80 dup(?)

.code

Main proc

        mov ax,@data

        mov ds, ax

        mov es, ax

        mov ah,9

        lea dx,tb1

        int 21h

        xor cx,cx

        lea di,xau

nhap:        mov ah,1

        int 21h

        cmp al,13

        je thoi

        cmp al,'A'

        jb dung

        cmp al,'Z'

        ja dung

        jmp nhap

dung:        stosb

        inc cx

        jmp nhap

thoi:        mov ah,9

        lea dx,tb2

        int 21h

        dec di

        mov si,di

        std

        mov ah,2

quay:        lodsb        

        mov dl,al

        int 21h

        loop quay

        mov ah,4ch

        int 21h

Main endp

        End main

The code above runs very well, even though i did not use the Clear Direction Flag (cld) instruction after the instruction in red (lea di,xau)
The string processing is still in forward direction.
The question is that: Why?

I appreciate your help.

Regards,
Duy.

Duy V. Nguyen
ODWME/Bluebird Project Leader- GPSG - IBM
Summers, NY 10589-3216
United States