ABSTRACT
SafetyNET p is a communication protocol that enables the transmission of safety-related data on the same cable used for the transfer of control or process data. The general structure of SafetyNET p frames consists of a 1-byte header section and a variable-size payload. SafetyNET p implements two communication models, known as real-time frame line (RTFL) and real-time frame network (RTFN). Synchronization of RTFN devices and RTFL networks is made possible by means of the precision time protocol (PTP) with the advantage that it is supported by many standard Ethernet components such as switches. Low jitter is achieved by means of a specialized synchronization mechanism, the so-called precise clock synchronization (PCS), which makes the protocol suitable for distributed processing that requires a high level of simultaneity. The SafetyNET p specification includes services to initialize and manage the communication. In the case of safe communications, either safety process data objects (SPDOs) or safety heartbeats (SHBs) are transmitted via cyclic data channel (CDC).
