Printing singed and unsigned numbers in Assembly

Question

I am doing an assembly lab for my school and its on printing signed and unsigned numbers. It keeps printing an infinite amount of "-/" but it should be printing a number. Is the offset for number to ascii value 30h?

    Display .EQU 04E9h

    NumAddr .EQU 0050h

Main:

    mov BX, NumAddr
    mov DX, Display

mainLoop:


    MOV AH,[BX]

    cmp AH, 0h        ; is number 0?
    JE  EndPrt        ; if yes we are done

    CMP AH,0h
    JG posNum         ; should jump to posNum if AH is positive

negNum:

    mov AL, 2Dh       
    out DX,AL         ; print a negative sign

    NEG AH            ; turn AH into a positive number

printPos:

    MOV AL,[BX]
    ADD AL, 30h       ; should add required offset to convert to ASCII
    out DX,AL

    MOV AL, 0Dh
    out DX,AL
    MOV AL, 0Ah
    out DX,AL

    inc BX

    jmp mainLoop

EndPrt:

    HLT

.END Main

score 0 · Answer 1 · answered Oct 03 '16 at 11:33

30h is offset of single digit. Ie. (4 + 30h) is 34h, and in ASCII encoding that is '4'. But for (17 + 30h) you will get 41h, which is character 'A'.

If you want two characters for value 17, like 31h '1' and 37h '7', you must split the number into separate base₁₀ (decimal) digits (dividing it by 10 and collecting remainders).

Printing singed and unsigned numbers in Assembly

1 Answers1