Logical difference between 2 8-bit ports XOR?

[circuitpro]

I'm trying to use XOR, and don't get it. I want an 8-bit binary number showing the difference between two 8-bit ports.... i.e. port X reads one thing, port Y reads another thing, how are they different. How do you do it, because this does not work...

     I2CREAD SDA1,SCL1,DJAM,[X]
     X=X^%11111111

     I2CREAD SDA1,SCL1,IRS,[Y]
     Y=Y^%11111111
     
     Z= (X XOR Y)
     
     DEBUG BIN8 Z,10,13

The ports are different, but this returns all 1's.

Thanks!