Zebra Open Safety

Fault identification and prevention

One of openSAFETY’s most crucial mechanisms is the time stamp, which prevents data duplications, mix-ups, and delays. Every data packet is stamped with the current time when it is sent. This stamp enables the receiver to avoid double read-outs, and to determine the chronological sequence of different packets as well as any delays. openSAFETY does not depend on distributed clocks; a special procedure provides for reliable synchronization of all microcontroller clocks within the nodes. Time monitoring is employed in order to prevent faults caused by data loss or excessive delays, i.e. the nodes are continuously monitored for live operation and proper functioning. In addition, as they are prompted for reply, Consumers can tell that the data link remains established. openSAFETY implements this mechanism, which is called “Watchdog,” as a software-based function. The identifier precludes any mix-ups on the receiving end: openSAFETY frames feature a unique, 8-bit or 16-bit identification tag that encodes parts of the address field, the telegram type contained, and the frame type. The most reliable means to identify changes to the original content is the CRC procedure, which uses a key to generate a checksum for each data set, and attaches that as well as the key as a bit sequence to the data set. This checksum is a distinctive encoding of the data set itself. Using the bit sequence and the key, the receiver calculates the original data set, and checks the result against the data set that was received in the clear. If any deviations from the original data content are detected, the message will be ignored.