As we don't know what your code looks like now, we can't give any more comment on how to fix it. Anyway, just a general comment of the way you've written the code in having all your variables in registers - this works fine for small pieces of code, but as soon as you try to expand your code, you're always tripping over what vars are stored in what register. To make things a little easier on yourself, always expect that A will get trashed - A is normally used to pass a byte value to your subroutine. I you read up on how a 'c' compiler passes variables (see Keil for info) and apply the same rules to your assembler code, this should make your coding a lot easier and less bug prone. Don't get too worried about efficiency - use techniques that help you write code that works through minimising bugs. When I first started coding, I used to write the most tightest,cryptic code and spent most of my time fixing bugs - sounds familiar??