Unable to access array data x86 assembly

Question

I have the following assembly code. I've declared two arrays in my DS. Later in the code I move into BX the index number of the array element I want to access. The PRINT_CHAR process just sends the data in AL over a serial port to display on the screen. But for some reason, I can't seem to access the array elements. It just gives me some bogus value. The print_char process is definitely fine. I've tried both methods I know to access the array. Any help would be appreciated. Thanks!

    DATA_SEG    SEGMENT
ARRAY       DB  '1','2','3','1','2','3','4','5','6','4','5','6'
bottom2     DB  '7','8','9','7','8','9','*','0','#','*','0','#'
    DATA_SEG    ENDS



    topnumbers:
    cmp BX, 12
    jge bottom_numbers
    MOV AL,DS:ARRAY[BX] ; Stores character in AL (?)
    jmp NUMBERS

    bottom_numbers:
    sub BL, 12d
            LEA SI, bottom2
            ADD SI, BX
            MOV AL, [SI]

    NUMBERS:
    XOR AH, AH
    CALL FAR PTR PRINT_CHAR

What have you set DS to?

Michael
– Michael

2013-10-21 07:33:44 +00:00
Commented Oct 21, 2013 at 7:33 — Michael
– Michael, Commented Oct 21, 2013 at 7:33
cannot believe i didnt realise that. thank you!

user2902028
– user2902028

2013-10-21 08:08:37 +00:00
Commented Oct 21, 2013 at 8:08 — user2902028
– user2902028, Commented Oct 21, 2013 at 8:08

johnfound · Accepted Answer · 2013-10-21 07:50:59Z

1

If you are creating .exe file, you are responsible to set the segment registers to the corresponding values. Something like (but check your secret assembler syntax as well):

    mov  ax, DATA_SEG
    mov  ds, ax

Besides, the above, for such small programs .COM executable format is much easier to handle, because DOS will set all segment registers for you and you will never need to use far pointers.

answered Oct 21, 2013 at 7:50

johnfound

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