The purpose of this Aerospace Recommended Practice (ARP) is to provide recommendations on the use of four types of discrete signal interfaces for unidirectional@ low power@ low frequency transmission of discrete information.Technical Information:This ARP provides techinal and application information needed by the designers of aircraft electric systems and support equipment for the selection of discrete signal interface methods. It provides the definitions to permit comparisons of various electric discrete signal interface methods.Field of Application:For reliable uniderectional signaling system transmission of the status of electrical information@ the selected method should provide enhanced performance againts lightning or electromagnetic pulse induced transients and fault propagation suppression to assure adequate simple aircraft subsystems. Preferred types of functional and electromagnetic compatibility methods should be utilized as an essential safety of flight requirements.