AKD EtherCAT | 4 EtherCAT Profile
4.13 Mailbox Handling
With EtherCAT, acyclical data traffic (object channel or SDO channel) is called mailbox.
Available SDO objects are listed in the ("Appendix" (
This system is based around the master:
Mailbox Output:
The master (EtherCAT controller) sends data to the slave (drive). This is essentially a
(read/write) request from the master. Mailbox output operates via Sync Manager 0.
Mailbox Input:
The slave (drive) sends data to the master (EtherCAT controller). The master reads the
slave's response. Mailbox input operates via Sync Manager 1.
Timing diagram
The timing diagram illustrates the mailbox access process:
1. The EtherCAT master writes the mailbox request to the mail-out buffer.
2. On the next interrupt, the EtherCAT interface activates a Sync Manager 0 event (mailbox
output event) in the AL event register.
3. The drive reads 16 bytes from the mail-out buffer and copies them to the internal mailbox
output array.
4. The drive identifies new data in the internal mailbox output array and performs an SDO
access to the object requested by the EtherCAT interface. The response from the drive is
written to an internal mailbox input array.
5. The drive deletes all data in the internal mailbox output array so that a new mailbox
access attempt can be made.
6. The drive copies the response telegram from the internal mailbox input array to the mail-in
buffer of the EtherCAT interface.
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Kollmorgen | kdn.kollmorgen.com | October 2017
