8 Operation8-48.2 EtherCAT State MachineThe EtherCAT State Machine (ESM) is responsible for the coordination of master and slave applications atstart up and during operation. State changes are typically initiated by requests of the master.The states of the EtherCAT State Machine are as follows.Power ON INITPRE-OPERATIONAL(PREOP)SAFE-OPERATIONAL(SAFEOP)OPERATIONAL(OP)(IP)(PI)(SP)(PS)(OP)(OI)(SI)(SO) (OS)State DescriptionINIT • No mailbox communication is possible.• No process data communication is possible.INIT => PREOP• Master configures DL Address and SyncManager channels for Mailbox communication.• Master initializes DC clock synchronization.• Master requests ‘Pre-Operational’ state.• Master sets AL Control register.• Slave checks whether the mailbox was initialized correctly.PREOP • Mailbox communication is possible.• No process data communication is possible.PREOP => SAFEOP• Master configures SyncManager channels and FMMU channels for process data.• Master configures PDO mapping and the sync manager PDO assignment parameters viaSDO.• Master requests ‘Safe-Operational’ state.• Slave checks whether the sync manager channels for process data communication and, ifrequired, the distributed clocks settings are correct.SAFEOP• Mailbox communication is possible.• Process Data communication is possible, but only Inputs are evaluated – Outputs remain in‘Safe’ state.SAFEOP => OP • Master sends valid Outputs.• Master requests ‘Operational’ state.OP • Mailbox communication is possible.• Process data communication is possible.
