xor flags, 01000000b ; Reverse bit
; Similar instructions will work whenever the second operand of mod is a power of 2
and eax, 0000001fh ; EAX Mod 32
; This will work
sub al, 30h ; ASCII to Integer (Common)
; But if you don't know whether the source is a ASCII or a numeric string, you can use the one below
and al, 00001111b ; ASCII to Integer (Better)