This standard specifies requirements for a bit-oriented interface system between a single controlling device and control circuit devices or switching elements as defined in EN 60947-1, connected by an unshielded, untwisted two-wire cable carrying data and power. It also enables the interchangeability of components which have such interfaces. This standard specifies: - requirements for interfaces and for electromechanical structures for slaves and masters; - performance of slaves, electromechanical structures and masters under normal service conditions; - constructional and performance requirements; - tests to verify conformance to the requirements. Specific requirements for the various profiles for slaves and masters are given in annexes A and B.