Subtraction example: mov al, 0x31 sub al, 0x08 das Will result in al = 0x23. And finally, an example equivalent to the first subtraction example: mov al, 0x31 add al, 0x92 daa Which will also result in al = 0x23. Here is a fixed solution: cmp al, 0xa ; Check if al is an 'a' - 'f' digit cmc ; Complement the carry adc al, 0x30 daa So, if we have a numeric digit ('0' - '9') in al, the first two