Static lookup table but only ouput what's changed

This is an extension/enhancement of a question I asked a while back and it provides all the code & context hopefully.

I have the lookup table in the question linked above running nicely - what I'd like to do now is have a look at how I can optimise my code so that only the bits that have changed are output rather than all 8 bits at a time.

Should I be looking at holding the state of a bit in a Db? (If so I already have them in MongoDb) or something more simple?

Any advise, pointers or examples would be great.