openSAFETY was designed aiming at transmission of safety relevant data over any field bus or network. It can be used on all field buses, Ethernet-based or not.
For the transmission of safety data, the producer-consumer model is used. The advantage of this model is that all consumers in an openSAFETY network can receive and subsequently process the messages sent by the producer. Each openSAFETY node has a unique UDID (openSAFETY Unique Device Identification) number. This is a combination of the MAC address and the manufacturer’s device number. During the booting process, the Safety Network Management (SNMT) checks the device type and the UDID, so that it automatically detects replaced devices. In such a case, the required parameters are automatically transferred to the Safety Nodes (SN). The SNMT can optionally be integrated with the Safety Configuration Manager (SCM). In analogy to other communication protocols, the SCM can be viewed as an openSAFETY master using services to manage the network.
The openSAFETY Object Dictionary (SOD) manages all parameters, which are then transferred to the safety nodes using Safety Service Data Objects (SSDO). Upon completion of Node configuration and the booting phase, the cyclic data transfer between producer and Consumer commences. For the transfer of safety-critical process data, this uses Safety Process Data Objects (SPDO). The openSAFETY frame consists of two sub frames. It can transport a maximum of 254 bytes of safety data, using CRC 8 for payloads from 1 to 8 bytes and CRC 16 for payloads from 9 to 254 bytes.
With openSAFETY, very large networks can be created. For each openSAFETY Domain (SD), up to 1023 safe nodes can be connected. As they are addressed by the SCM, no additional hardware switches are required. The maximum total configuration of an openSAFETY network has 1023 openSAFETY Domains with a total of more than a Million safe nodes. Communication between the individual Domains is performed by the openSAFETY Domain Gateway (SDG).