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4
EtherCAT interface
62
Festo – GDCP-CMMP-M3/-M0-C-CO-EN – 1510b – English
4.7
Communication Finite State Machine
As in almost all fieldbus interfaces for motor controllers, the connected slave (in this case the motor
controller CMMP-AS-...-M3) must first be initialised by the master before it can be used by the master in
an application. For this purpose, a finite state machine is defined for communication, to specify a fixed
sequence of actions for this initialisation process.
A finite state machine is also defined for the EtherCAT interface. Changes between the individual
statuses of the finite state machine may only occur between specific statuses, and are always initiated
by the master. Slaves may not implement status changes independently. The individual statuses and
the permitted status changes are described in the following tables and figures.
Status
Description
Power ON
The device has been switched on. It initialises itself and switches directly to the
“Init” status.
Init
In this status, the EtherCAT fieldbus is synchronised by the master. This includes
setting up the asynchronous communication between master and slave (mailbox
telegram protocol). There is no direct communication between the master and
slave yet.
The configuration starts, saved values are loaded. When all devices are con
nected to the bus and configured, the status switches to “Pre-Operational”.
Pre-Operational
In this status, asynchronous communication between the master and slave is
active. The master uses this status to set up possible cyclic communication via
PDOs and use acyclic communication for necessary parametrisation.
If this status runs without errors, the master switches to the “Safe-Operational”
status.
Safe-Operational
This status is used to set all equipment connected to the EtherCAT bus to a safe
status. The slave sends up-to-date actual values to the master but ignores new
setpoint values from the master and uses safe default values instead.
If this status runs without errors, the master switches to the “Operational”
status.
Operational
In this status, both acyclic and cyclic communication are active. Masters
and slaves exchange target and actual value data. In this status, the
CMMP-AS-...-M3 can be enabled and travel via the CoE protocol.
Tab. 4.9
Statuses of communication finite state machine