1.2 Introduction to EtherCAT
1.2.3 Sending and Receiving Data in EtherCAT (CoE) Communications
1-4
1.2.3
Sending and Receiving Data in EtherCAT (CoE) Commu-
nications
Objects are used to send and receive data in EtherCAT (CoE) communications.
Reading and writing object data is performed in process data communications (PDO service),
which transfers data cyclically, and in mailbox communications (SDO service), which transfers
data non-cyclically.
Process data communications are used to read and write PDOs. Mailbox communications
(SDO) are used to read and write object dictionary data entries.
1.2.4
CoE Terminology
The EtherCAT and CANopen terms that are used in this manual are described in the following
table.
Term
Abbreviation
Description
CAN in Automation
CiA
A non-profit organization established in 1992 as a joint ven-
ture between companies to provide CAN technical informa-
tion, product information, and marketing information.
Controller Area Network
CAN
Communications protocol for the physical layer and data link
layer established for automotive LANs. It was established as
an international standard as ISO 11898.
CANopen
CANopen
An upper-layer protocol based on the international CAN stan-
dard (EN 50325-4).
It consists of profile specifications for the application layer,
communications, applications, devices, and interfaces.
CANopen over EtherCAT
CoE
A network that uses Ethernet for the physical layer, EtherCAT
for the data link layer, and CANopen for the application layer
in a seven-layer OSI reference model.
Distributed Clocks
DC
A clock distribution mechanism that is used to synchronize
the EtherCAT slaves with the EtherCAT master.
Electrically Erasable
Programmable Read Only
Memory
EEPROM
A ROM that can be electrically overwritten.
EtherCAT Slave Controller
ESC
A hardware chip that processes EtherCAT communications
(such as loopbacks) and manages the distributed clock.
EtherCAT State Machine
ESM
A state machine in which the state of EtherCAT (the data link
layer) changes according to transition conditions.
EtherCAT Technology Group
ETG
An international organization established in 2003 to provide
support for developing EtherCAT technologies and to pro-
mote the spread of EtherCAT technologies.
Ethernet for Control
Automation Technology
EtherCAT
An open network developed by Beckhoff Automation.
Fieldbus Memory
Management Unit
FMMU
A unit that manages fieldbus memory.
INIT
INIT
The Init state in the EtherCAT state machine.
OPERATIONAL
OP
The Operational state in the EtherCAT state machine.
Object Dictionary
OD
A group of objects and structure supported by an EtherCAT
SERVOPACK.
Process Data Object
PDO
Objects that are sent and received in cyclic communications.
Process Data Object
Mapping
PDO mapping
Definitions of the applications objects that are sent with
PDOs.
Service Data Object
SDO
Objects that are sent and received in mailbox communica-
tions.
PRE-OPERATIONAL
PREOP
The Pre-operational state in the EtherCAT state machine.
Process data
–
The data contained in application objects that are periodically
transferred for measurements or controls.
Continued on next page.