In To Kill a Mockingbird, what are the unwritten social codes that Atticus adheres to in his life?

Understand first of all that there are many "unwritten
social codes" that most characters adhere to in the story (and historically would have
adhered to if they were real people).  Ironically, Atticus does not
act like most of the other characters.  His social codes are far different from the
social codes of most people.

For one thing, he is the
arguably one of the the least prejudiced characters in the story.  He teaches his
children how to respect everyone equally.  One unwritten social code of that time was to
respect people according to social "levels."  Prejudice was not limited to race alone. 
It was also related to education, perceived "wealth," family relations, and land
ownership.  Through Atticus' teaching, Jem and Scout are able to understand and observe
the differences among the different social classes, but Atticus teaches them to go
against the social codes that tell them to look down on people who are
different.

Another unwritten social code of that time would
have told him to stay away from the Tom Robinson trial.  He takes it and fights it
fairly, to the best of his ability.  In a way, he is choosing to follow a
legal social code (one that lawyers and judges
should be abiding by) to hold up the law and provide the best
defense he can for his client.

On the other hand, Atticus
does do a few things that would have been considered adhering to
unwritten social codes.  First, in the absence of a wife/mother, he hires Calpurnia, an
older black woman, to take care of his kids and household matters.  It was probably more
appropriate to do this than to hire a white woman.  He teaches his children to respect
her, as well as all other adults, simply because they are older.  This was a social code
of the time that is no longer prominent today.

Also, he
allows his sister (Aunt Alexandra) to come for a while in order to provide a maternal
influence for the children.  Again, it would have been a common practice to send in for
family help in the Finch's situation with the trial.  Finally, in the chapter where Dill
shows up unexpectedly, Atticus allows him to stay.  He is abiding by an unwritten social
code here to provide some paternal influence for a child who does not have a
relationship with a father.