Hi,
I was doing the same thing as you too last time. As far as I know, some of the reader using "pack binary" as data to save the spaces. For your information, Pack binary meant use one byte HEX (01-FF)to represent 2 digits numeric data. You may need to convert it back and forth.
Hope it helps
I am not the most powerful man in this world.
I am not the worst man in this world either.
I just as same as all of you.
I still need to learn from my mistakes...