Sec. 7. (a) A person who knowingly or intentionally fails to provide support to his parent, when the parent is unable to support himself, commits nonsupport of a parent, a Class A misdemeanor.
(b) It is a defense that the accused person had not been supported by the parent during the time he was a dependent child under eighteen (18) years of age, unless the parent was unable to provide support.
(c) It is a defense that the accused person was unable to provide support.