Cyclic process data exchange
The cyclic process data, which are written and read synchronously and consistently in the network, are defined by the configuration tool.
A master can support several cycle tasks (sync units) that contain different cycle times and/or different frame lengths.
With EtherCAT®, any data of individual or various stations can be logically combined to so-called sync units. The data are grouped by means of the modularity of the control application. The grouping is not subjected to the rather arbitrary arrangement of I/O modules. Each sync unit contains a diagnostic input information (sync unit state) that is updated cyclically. The sync unit state indicates whether the data were exchanged successfully.
If a slave in a sync unit fails, the process data of the respective sync unit will become invalid. The process data of the other sync units remain valid.
Several sync units are useful in applications where parts of the machine have to run although other units are faulty, have been removed, switched off, or disabled. Several sync units allow for a modular system structure.
