我试图弄清楚如何将十六进制数转换为二进制补码十六进制。我已经对该字符作为十六进制数字进行了所有必要的检查，并将其转换为ASCII代码的数字代码，但是当我尝试打印转换后的Tow的补码时，它给我带来了意外的结果，我觉得我在此代码中缺少了一些内容。有人可以帮忙谢谢你吗？

INCLUDE Irvine32.inc
.data

   var1 db "A",0
   var2 db "error",0

   char1 db ?

.code
main PROC

    mov  edx,OFFSET var1    ; get starting address of string

L1:
    mov  al,BYTE PTR [edx]  ; get next character
    inc  edx                 ; increment pointer
    test al,al              ; test value in AL and set flags
    jz   Finished            ; AL == 0,so exit the loop

    ; Otherwise,AL != 0,so we fell through.
    ; Here,you can do something with the character in AL.
    ; ...

    cmp al,30h               ; compare it with 30H - ASCII CODE OF 0
    jb  error                 ; if charater is below 30H - then error

    cmp al,39H               ; compare it with 39H - ASCII code of 9
    ja  Big                   ; if charater is above 30H 
                              ; check for A-F
    jmp comp                  ; otherwise,go for Conversion of ASCII code
Big:
    cmp al,41H               ; compare al with 41H - ASCII code of A
    jb  error                 ; if code is below 41h,then error

    cmp al,46H               ; compare al with 46H - ASCII code of F
    ja Small                  ; if code is above 46h,check for A-F

    jmp comp                  ; otherwise,go for Conversion of ASCII code
                              ; to numric value 
Small:
    cmp al,61H               ; compare al with 46H - ASCII code of a
    jb  error                 ; if code is below 61H,66H               ; compare al with 46H - ASCII code of f
    ja error                  ; if code is above 66h,then error

comp:
    sub al,30H               ; subtract 30H - numeric code
    cmp al,09H               ; compare if al is in range of 0-9
    jbe next                  ; then jump to next to store back to Hex Array

    sub al,07H               ; otherwise,for A-F,7H has to be subtracted
    cmp al,0FH               ; compare the value is in range of A-F

    jbe  next                 ; then jump to next to store back to Hex Array
    sub al,20H               ; otherwise for a-f,subtract additional 20H
next: 
    not al                    ; get 1's complement 
    add al,00000001b         ; add 1 to get 2't complement

    mov char1,al
    jmp L1



error:
    mov edx,OFFSET var2      ; display error massage
    call writestring

Finished:
    mov edx,OFFSET char1
     call writestring


    exit
main ENDP

END main