A digital code having two information states, e.g., "0" and "1" or "mark" and "yyspace", in which code the signal returns to a rest state during a portion of the bit period. 2. A code form having two information states termed "zero" and "one" and having a third state or an at-rest condition to which the signal returns during each rest period. In this specification, the at-rest condition is the zero state.