BECKHOFF EtherCAT Technology Section I - Manual (Page 63)

SyncManager
Slave Controller – Technology I-43
The Status register of the SyncManager reflects the current state. The last written buffer is indicated
(informative only, access redirection is performed by the ESC), as well as the interrupt states. If the
SyncManager buffer was not written before, the last written buffer is indicated to be 3 (start/empty).
8.2 Mailbox Mode
The mailbox mode only allows alternating reading and writing. This assures all data from the producer
reaches the consumer. The mailbox mode uses just one buffer of the configured size.
At first, after initialization/activation, the buffer (mailbox, MBX) is writeable. Once it is written
completely, write access is blocked, and the buffer can be read out by the other side. After it was
completely read out, it can be written again.
The time it takes to read or write the mailbox does not matter.
Master µController
Write Mailbox
Write 
Write w. failure
(Mailbox full)
Mailbox full
Mailbox empty
 Read
 Read w. failure
(Mailbox empty)
Read Mailbox
Read 
Read w. failure
(Mailbox empty)
Mailbox full
Mailbox empty  Write
Write w. failure
(Mailbox full)
Figure 24: SyncManager Mailbox Interaction
8.2.1 Mailbox Communication Protocols
This is only a brief overview of the mailbox communication protocols. For details on the mailbox
protocols refer to the
EtherCAT specification ETG.1000.6: “Application layer protocol specification”
available from the EtherCAT Technology Group ( http://www.ethercat.org ) or to the IEC specification
“Digital data communications for measurement and control – Fieldbus for use in industrial control
systems”, IEC 61158 Type 12: EtherCAT, available from the IEC (
http://www.iec.ch ).
Ethernet over EtherCAT (EoE)
Defines a standard way to exchange or tunnel standard Ethernet Frames over EtherCAT.
CAN application layer over EtherCAT (CoE)
Defines a standard way to access a CAN application layer object dictionary and to exchange CAN
application layer Emergency and PDO messages on an event driven path.
File Access over EtherCAT (FoE)
Defines a standard way to download and upload firmware and other ‘files’.
Servo Profile over EtherCAT (SoE)
Defines a standard way to access the IEC 61800-7 identifier.
Vendor specific Profile over EtherCAT (VoE)
A vendor specific protocol follows after a VoE header that identifies the vendor and a vendor specific
type.
ADS over EtherCAT (AoE)
AoE defines a standard way to exchange Automation Device Specification (ADS) messages over
EtherCAT.