I take it you're looking for a Hamming Distance or something. You can get a value with a zero in each bit that is different by using XOR. If you want to deal with ones, then invert it. You can count by setting up a loop and applying an AND mask for each bit, successively, or you can use shift/rotate and count when the carry flag is set after each shift/rotate. I haven't written 8085 assember in about 15 years, so I'm not posting actual code.