scope:

NEN-EN-IEC 61158-4-19 provides basic time-critical messaging communications between devices in an automation environment. This protocol provides communication opportunities to all participating data-link entities a) in a synchronously-starting cyclic manner, according to a pre-established schedule, and b) in a cyclic or acyclic asynchronous manner, as requested each cycle by each of those data-link entities. Thus this protocol can be characterized as one which provides cyclic and acyclic access asynchronously but with a synchronous restart of each cycle. Specifications This standard specifies a) procedures for the timely transfer of data and control information from one data-link user entity to a peer user entity, and among the data-link entities forming the distributed datalink service provider; b) the structure of the fieldbus DLPDUs used for the transfer of data and control information by the protocol of this standard, and their representation as physical interface data units.