Ethercat State Machine; Fig. 9 Ethercat State Machine - Beckhoff EP3356-0022 Documentation

Basics of communication
3.3

EtherCAT State Machine

The state of the EtherCAT slave is controlled via the EtherCAT State Machine (ESM). Depending upon the
state, different functions are accessible or executable in the EtherCAT slave. Specific commands must be
sent by the EtherCAT master to the device in each state, particularly during the bootup of the slave.
A distinction is made between the following states:
• Init
• Pre-Operational
• Safe-Operational and
• Operational
• Boot
The regular state of each EtherCAT slave after bootup is the OP state.
Fig. 9: EtherCAT State Machine
Init
After switch-on the EtherCAT slave in the Init state. No mailbox or process data communication is possible.
The EtherCAT master initializes sync manager channels 0 and 1 for mailbox communication.
Pre-Operational (Pre-Op)
During the transition between Init and Pre-Op the EtherCAT slave checks whether the mailbox was initialized
correctly.
In Pre-Op state mailbox communication is possible, but not process data communication. The EtherCAT
master initializes the sync manager channels for process data (from sync manager channel 2), the FMMU
channels and, if the slave supports configurable mapping, PDO mapping or the sync manager PDO
assignment. In this state the settings for the process data transfer and perhaps terminal-specific parameters
that may differ from the default settings are also transferred.
Safe-Operational (Safe-Op)
During transition between Pre-Op and Safe-Op the EtherCAT slave checks whether the sync manager
channels for process data communication and, if required, the distributed clocks settings are correct. Before
it acknowledges the change of state, the EtherCAT slave copies current input data into the associated DP-
RAM areas of the EtherCAT slave controller (ECSC).
20 Version: 1.1.0 EP3356-0022