EtherCAT: How are SM0 & SM1 sync managers typically used?

In EtherCAT, the sync managers SM0 and SM1 are typically used for CoE (CANOpen over EtherCAT) mailbox communication. Essentially, mailbox communication is used for non-cyclic data exchange between the EtherCAT master and the slave devices.

• SM0 is typically used as MbxIn (Mailbox Input), that is, for Master->Slave communication
• SM1 is typically used as MbxOut (Mailbox receive), that is, for Slave->Master communication

For details you should check your EtherCAT slave’s ESI file (EEPROM specification) or the ESI XML file which can often be downloaded from the manufacturer’s website.

Source: Beckhoff website and ETG1000.6 V1.0.32, section 5.6.7.4.9 (requires free ETG membership).

Table 75 in ETG1000.6 V1.0.32 (section 5.6.7.4.9) lists that sync managers shall be used with the following SyncManager communication types:

• SM0: Mailbox Receive (communication type 0x01)
• SM1: Mailbox Send (communication type 0x02)
• SM2: Process Data Output (communication type 0x03) (can be used for Inputs if Outputs not supported)
• SM3: Process Data Input (communication type 0x04)

Only if mailbox is not supported for the given slave, sync managers shall be used in the following way:

• SM0: Process Data Output (communication type 0x03) (may be used for Inputs if Outputs not supported)
• SM1: Process Data Input (communication type 0x04)