TPM
207-D522-NN User Manual
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4.4
ESM (EtherCAT State Machine)
The EtherCAT State machine (ESM) is used to manage the communications states between the master and
slave applications when EtherCAT communications are started and during operation, as show in the following
figure.
Normally, the requests of state changes are from the master. The master requests the change by writing the
ESM with the request to be changed in the AL control register of the slaves. The slave confirms the result of
the state change as either successful or failed and then responds to the master with the local AL status. If the
requested state change fails, the slave responds with an error flag.
Init
Pre_Operational
Bootstrap
Safe-Operational
Operational
Safe-Operational
(OI)
(OP)
(PI)
(OS)
(SP)
(SI)
(BI)
(IB)
(SO)
(PS)
(IP)
Power On
⚫
ESM contains states
Symbol
Name
Communication Operation
Description
INIT
Init
The communication part is
initializing and the transmission
and reception with both SDO
(Mailbox) and PDO are
impossible
INIT state defines basic communication relation
between the master and slave in the application layer.
Direct communication between the master and slaves
is not possible in the application layer. The master
uses the INIT state to initialize the setting for the
configuration of the slaves. When the slaves support
the mailbox service, the corresponding SM settings
will also be executed in INIT state.
PREOP
Pre-
Operational
Possible to send and receive data
through SDO (Mailbox)
The mailbox communication can be performed in the
PREOP state when the slaves support the optional
mailbox. Both master and slaves can use the mailbox
to initialize application specifications and to change
parameters. Process data communication cannot be
executed in this state.