Beckhoff EP3356-0022 Documentation page 21

Basics of communication
Mailbox and process data communication is possible in the Safe-Op state, but the slave keeps its outputs in
the safe state. However, the input data are cyclically updated.
Operational (Op)
Before the EtherCAT master switches the EtherCAT slave from Safe-Op to Op it must transfer valid output
data.
In the Op state the slave copies the output data of the masters to its outputs. Process data and mailbox
communication is possible.
Boot
In the Boot state the slave firmware can be updated. The Boot state can only be reached via the Init state.
In the Boot state mailbox communication via the file access over EtherCAT (FoE) protocol is possible, but no
other mailbox communication and no process data communication.
EP3356-0022 Version: 1.1.0 21