21.4.12 Mailbox Handling
With EtherCAT, acyclical data traffic (object channel or SDO channel) is called mailbox. 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. Mail-
box 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.
AKD User Guide |
Kollmorgen | December 2010 58
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