EtherCAT Glossaries

EtherCAT master

The EtherCAT master controls multiple EtherCAT slaves within an EtherCAT network.
There are 2 types of EtherCAT masters. One is the software master stack that runs under the OS and the other is the master that contains an interface card with an EtherCAT master function. Either type of master supports both the process data communication and mailbox communication.
The process data communication transmits frames containing commands and data with a cyclic manner. And the mailbox communication sends and receives data between the master and slaves with a non-cyclic manner.

EtherCAT slave

A slave reads the data in the frame that is sent from the master and writes the data to a frame that is addressed to the master on-the-fly. The frame with the data is passed from the slave to an adjacent slave in the daisy-chain and travels through all the slaves in the network delivering the data.

Process data communication

In EtherCAT, process data communication is a communication method where the master transmits data to all the slaves in a cyclic manner at once. The transmitted frame travels through all the slaves until it reaches the last slave in the network and is then returned to the master following the same route. Each slave reads the data in the frame that is addressed to it , and also writes data to the frame destined for the master.

Mailbox communication

Mailbox communication on the EtherCAT is a non-cyclic communication from the master to a specific slave. The transmitted frame travels through all the slaves following the same path as the process data communication but the data contained in a frame is addressed only to a specific slave.


PDO stands for Process Data Object and is a communication method that uses the process data communication method. In PDO, fixed length data is sent to all the slaves at once. The frame length and format are determined by the PDO configuration of the connected slave(s). Consequently, frames sent from the master must contain frames with data as well as empty frames to carry back the data from the slaves in the network.
Each slave writes its data to the empty frame before sending it back to the master.


SOD stands for Service Data Object and is a communication method that uses the mailbox communication method. SDO enables you to use not only the EtherCAT protocol but also other protocols and their profile data. For example, you can use such protocols as CANopen (CoE), Ethernet (EoE), File Access (FoE), Sercos (SoE), and Vendor Specific (VoE).


CoE stands for CANopen over EtherCAT. Data that uses the CoE protocol is transferred by either SDO or PDO and refers to the OD (object dictionary).

CiA402 driver profile

CiA402 drive profile is compliant with the device profile for drive and motion controls as specified in IEC 61800-7-201 and IEC 61800-7-301. Hivertec's EtherCAT slave series uses this profile for the definition of the controller’s functional operation. The CiA402 compliant models support profile position mode, profile speed mode, speed mode, and homing mode.


The ESC stands for EtherCAT Slave Controller. It extracts only the data destined only to itself in the EtherCAT communication packet sent from the master, at the same time it writes the data to the packet destined to the master before passing the packet to the next slave on the network. The ESC exchanges data with the CPU within the slave using DPRAM (Dual Port RAM).


The SM stands for Sync. Manager. SM will receive or transmit port of data to be communicated by process data communication or mail box communication.
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